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http://www.archive.org/details/manualofpractica1912cunn 


MANUAL    OF   ANATOMY 


.PUBLISHED  BY  THE  JOINT  COMMITTEE  OF   HENRY  FROWDE  AND  HODDER  &  STOUGHTON 
AT    THE    OXFORD    PRESS    WAREHOUSE,    FALCON    SQUARE,    LONDON,     E.C. 


MANUAL 


OF 


Practical  Anatomy 


BY 


The  Late  D.  J.    CUNNINGHAM 

M.D.  (eDIN.  ET  duel.),   D.SC,    LL.  D.  (ST.  AND.   ET  GLAS.),  D.C.L.    (OXON.),  F.R.S. 
LATE   PROFES%OR   OF   ANATOMY   IN   THE   UNIVERSITY   OF   EDINBURGH 


Fl  FTH     EDITION 


EDITED   BY   ARTHUR    ROBINSON 

PROFESSOR   OF   ANATOMY   IN   THE    UNIVERSITY    OF    EDINBURGH 


VOLUME    SECOND 
THORAX;  HEAD  AND  NECK 


WITH  236   ILLUSTRATIONS 


NEW    YORK 
WILLIAM   WOOD   AND   COMPANY 

MDCCCCXII 


cm  2. 

\l-  2- 


PREFACE    TO    FIFTH    EDITION 


The  main  object  of  this  preface  is  to  thank  those  who  have 
so  kindly  assisted  me  in  the  production  of  the  book.  At  the 
same  time,  it  may  be  pointed  out  that  the  reasons  for  the 
adoption  of  the  Basle  nomenclature  were  fully  stated  in  vol.  i., 
and  that  the  alterations  which  have  been  made  in  the  plans 
of  dissection  in  vol.  ii.  are  not  less  numerous  than  those  made 
in  vol.  i.  The  alterations  include  changes  in  the  method  of 
dissecting  the  face,  the  posterior  triangle,  and  the  deeper 
parts  of  the  neck.  Two  plans  of  dissection  to  display  the 
middle  ear  and  its  surroundings  are  described.  They  can  be 
carried  out  on  opposite  sides  of  the  head,  and  the  steps  of 
the  second  method  are  those  followed  by  the  surgeon  operat- 
ing for  the  relief  of  mastoid  and  middle  ear  disease.  The 
dissection  of  the  thorax  has  been  very  largely  re-arranged 
with  the  object  of  giving  the  dissector  an  opportunity  of 
studying  the  relative  positions  of  the  organs  in  the  medi- 
astinum whilst  they  are  practically  undisturbed. 

The  various  plans  of  dissection  described  were  decided 
upon,  after  many  trials,  as  those  best  adapted  to  give  the 
student  a  clear  idea  of  the  relative  positions  of  important 
structures ;  and  I  am  greatly  indebted  to  my  first  and  second 
assistants.  Dr.  E.  B.  Jamieson  and  Mr.  T.  B.  Johnston,  and 
to  Professor  R.  B.  Thomson  of  Cape  Town,  for  the  trouble 
they  have  taken  and  the  help  they  have  given  in  devising, 
modifying,  and  testing  new  plans  of  work. 

I  am  indebted  also  to  Dr.  Jamieson  for  dissections  of  the 
brain  and  heart ;  to  Mr.  Johnston  for  the  dissections  of  the 
parotid  gland ;  to  Mr.  W.  W.  Carlow  for  a  dissection  of  the 
mediastinum ;  and  to  Messrs.  M.  Barseghian,  R.   C.   Rogers, 

V 


vi  PREFACE  TO  FIFTH  EDITION 

and  F.  M.  Halley  for  other  dissections  upon  which  they 
have  expended  time  and  skill,  and  which  have  been  used 
in  the  preparation  of  the  new  illustrations. 

I  wish  also  to  thank  Professor  Arthur  Thomson  for  per- 
mission to  use  the  illustrations  of  his  beautiful  dissections  of 
the  eye ;  Professor  A.  M.  Paterson  for  permission  to  use  two 
diagrams  illustrating  the  connections  of  some  of  the  cranial 
nerves ;  and  Dr.  Logan  Turner  for  the  loan  of  the  specimens 
from  which  the  illustrations  of  the  dissection  of  the  mastoid 
region  and  middle  ear  were  made. 

All  the  new  illustrations  are  from  drawings  made  by  Mr. 
J.  T.  Murray.  They  are  characteristic  of  his  excellent  work, 
and  I  am  indebted  to  him  for  the  care  and  skill  he  has  ex- 
pended on  their  production. 

The  new  indices  and  the  glossary  are  the  work  of  Mr.  J. 
Keogh  Murphy,  F.R.C.S.  I  believe  they  will  prove  to  be  of 
great  service ;  and  I  desire  to  thank  him  not  only  for  the 
time  and  trouble  he  has  spent  upon  them,  but  also  for  many 
useful  suggestions  which  he  has  made  during  the  progress  of 
the  work. 

ARTHUR  ROBINSON. 

Edinburgh,  July  1912. 


CONTENTS 


THORAX. 


Introductory, 
Thoracic  Wall, 
Thoracic  Cavity, 
Thoracic  Joints, 


PAGE 
I 

3 

TO 
112 


HEAD  AND  NECK. 

Face  and  Frontal  Region  of  Head, 

Side  of  the  Neck, 

Posterior  Triangle, 

The    Scalp    and    the    Superficial     Structures    of    the 

Temporal  Region,     .... 
The  Dissection  of  the  Back,    . 
Removal  of  the  Brain,  .  .  . 

The  Anterior  Part  of  the  Neck, 
Temporal  and  Infratemporal  Regions, 
Submaxillary  Region,     .... 
Otic  Ganglion  and  Tensor  Palati,    . 
The  Great  Vessels  and  Nerves  of  the  Neck, 
The  Lateral  Part  of  the  Middle  Cranial  Fossa, 
Dissection  of  the  Orbit, 
Prevertebral  Region,     . 
The  Joints  of  the  Neck, 
Mouth  and  Pharynx, 
Carotid  Canal, 
Nervus  Maxillaris, 
Nasal  Cavities, 


117 
142 
142 

152 
161 
200 
222 
265 
279 
292 
294 
325 

•^  '-*  ■-> 

350 
356 
364 
385 
386 

389 


Vlll 


CONTENTS 


Spheno  -  Palatine    Ganglion 

Artery, 
The  Larynx, 
The  Tongue, 


AND    Internal    Maxillary 


402 
406 
429 


ENCEPHALON— THE  BRAIN. 

Membranes  and  Blood  Vessels  of  the  Brain, 
Base  of  Brain,      ..... 
The  Cerebrum,      ..... 
The  Mesencephalon,       .... 
Basal  Ganglia  of  the  Cerebral  Hemispheres, 
The   Parts  of  the   Brain   which   lie   in   the    Posterior 
Cranial  Fossa,  ...... 


439 

452 

459 
506 
512 

520 


THE  AUDITORY  APPARATUS. 

External  Meatus,  ..... 

Membrana  Tympani,         ..... 

Tympanic  Cavity  or  Middle  Ear, 

Auditory  Ossicles,  ..... 

Auditory  Tube,     .  .  .  . 

Intrapetrous  Part  of  the  Facial  Nerve  and  the  Acustic 
Nerve,  ....... 

-Vestibulum,  ...... 

Canales  Semicirculares  Ossei, 

The  Cochlea,    ...... 


547 
549 
550 
555 
559 

562 
566 

567 
567 


BULBUS  OCULL 

General  Structure  of  the  Eyeball, 

The  Sclera, 

The  Cornea, 

Tunica  Vasculosa  Oculi, 

The    Retina, 

The  Vitreous  Body, 

Lens  Crystallina, 

Chambers  of  the  Eyeball, 


571 
572 
573 
574 
579 
581 

583 
584 


INDEX, 


585 


A    GLOSSARY 


OF    THE 


INTERNATIONAL   (B.N.A.) 
ANATOMICAL    TERMINOLOGY 


GENERAL    TERMS. 
Terms  indicating  Situation  and  Direction. 


Longitudinalis      Longitudinal 
Verticalis  Vertical 


Anterior 
Posterior 
Ventral 


Dorsal 
Cranial 


Caudal 
Superior 

Inferior 
Proximalis 

Distalis 
Sagittalis 

Frontalis 


} 


Referring  to  the  long  axis  of  the  body. 
/-Referring  to  the  position  of  the  long 
I      axis  of  the  body  in  the  erect  posture. 
/'  Referring  to  the  front  and  back  of  the 
\     body  or  the  limbs. 
^Referring  to  the  anterior  and  posterior 
aspects,  respectively,  of  the  body, 
\      and    to    the    flexor    and    extensor 
{     aspects  of  the  limbs,  respectively. 
/'Referring  to  position  nearer  the  head 
I      or   the   tail  end  of  the  long  axis. 
"'l      Used  only  in  reference  to  parts  of 
I,     the  head,  neck,  or  body. 
Used  in  reference  to  the  head,  neck, 
and  body.      Equivalent    to  cranial 
and  caudal  respectively. 
Used  only  in  reference  to  the  limbs. 
Proximal  nearer  the  attached  end. 
Distal      J  '^      Distal  nearer  the  free  end, 

/-Used  in  reference  to  planes  parallel 
I      with    the    sagittal    suture    of    the 
Sagittal  -,       ^^^^Y,   i.e.   vertical  antero-posterior 

I     planes. 

rUsed  in  reference  to  planes  parallel 
Frontal  \      with  the  coronal  suture  of  the  skull, 

\      i.e.  transverse  vertical  planes. 

ix 


Anterior 
Posterior 
Ventral 


Dorsal 

Cranial 


Caudal  J 
Superior  ^ 

Inferior  j 
Proximal 


}    1 


GLOSSARY 


Horizontalis 

Horizontal 

Medianus 

Median 

Medialis 

Medial  ' 

Lateralis 

Lateral  J 

Intermedius 

Intermediate 

Superficialis 

Profundus 

Externus 

Superficial  \ 
Deep           i 
External  ■- 

Internus 
Ulnaris 

Internal  , 
Ulnar  \ 

Radial  is 
Tibial 

Radial 
Tibial    ^ 

Fibular 

Fibular] 

Used  in  reference  to  planes  at  right 

angles  to  vertical  planes. 
Referring    to     the     median     vertical 

antero-posterior  plane  of  the  body. 
■Referring     to     structures     relatively 

nearer  to  or  further  away  from  the 

median  plane. 
"Referring   to   structures   situated    be- 
tween   more     medial     and     more 

lateral  structures. 
Referring  to  structures  nearer  to  and 

further  away  from  the  surface. 
Referring,  with  few  exceptions,  to  the 

walls  of  cavities  and  hollow  organs. 

JVo^  to  be  used  as  synonymous  with 

medial  and  lateral. 
Used  in  reference  to  the  medial  and 

lateral    borders     of    the    forearm, 

respectively. 
Used  in  reference  to  the  medial  and 

lateral    borders    of    the    leg,     re- 
spectively. 


THE    BONES. 


B.N. A.  Terminology. 

Vertebrae 

Fovea  costalis  superior 

Fovea  costalis  inferior 

Fovea  costalis  transversalis 
Radix  arcus  vertebrae 

Atlas 

Fovea  dentis 

Epistropheus 

Dens 

Sternum 

Corpus  sterni 
Processus  xiphoideus 
Incisura  jugularis 
Planum  sternale 

Ossa  Cranii. 
Os  frontale 

Spina  frontalis 
Processus  zygomaticus 
Facies  cerebralis 
Facies  frontalis 


Old  Terminology, 

Vertebrae 

Incomplete  facet  for  head  of  rib, 

upper 
Incomplete  facet  for  head  of  rib, 

lower 
Facet  for  tubercle  of  the  rib 
Pedicle 

Atlas 

Facet  for  odontoid  process 

Axis 

Odontoid  process 

Sternum 

Gladiolus 
Ensiform  process 
Supra-sternal  notch 
Anterior  surface 

Bones  of  SkulL 

Frontal 

Nasal  spine 

External  angular  process 
Internal  surface 
Frontal  surface 


GLOSSARY 


XI 


B.N. A.  Terminology. 

Os  parietale 

Lineae  temporales 
Sulcus  transversus 
Sulcus  sagittalis 

Os  occipitale 

Canalis  hypoglossi 
Foramen  occipitale  magnum 
Canalis  condyloideus 
Sulcus  transversus 
Sulcus  sagittalis 
Clivus 

Linea  nuchse  suprema 
Linea  nuchce  superior 
Linea  nuchae  inferior 

Os  sphenoidale 

Crista  infratemporalis 

Sulcus  chiasmatis 

Crista  sphenoidalis 

Spina  angularis 

Lamina  medialis  processus  ptery- 
goids 

Lamina  lateralis  processus  ptery- 
goidei 

Canalis  pterygoideus  [Vidii] 

Fossa  hypophyseos 

Sulcus  caroticus 

Conchas  sphenoidales 

Hamulus  pterygoideus 

Canalis  pharyngeus 

Tuberculum  sellte 

Fissura  orbitalis  superior 

Os  temporale 

Canalis  facialis  [Fallopii] 
Hiatus  canalis  facialis 
Vagina  processus  styloidei 
Incisura  mastoidea 
Impressio  trigemini 
Eminentia  arcuata 

Sulcus  sigmoideus 
Fissura  petrotympanica 
Fossa  mandibularis 
Semicanalis  tubee  auditivae 

Os  ethmoidale 

Labyrinthus  ethmoidalis 
Lamina  papyracea 
Processus  uncinatus 


Old  Terminology. 

Parietal 

Temporal  ridges 
Groove  for  lateral  sinus 
Groove  for  sup.  long,  sinus 

Occipital 

Anterior  condyloid  foramen 
Foramen  magnum 
Posterior  condyloid  foramen 
Groove  for  lateral  sinus 
Groove  for  sup.  long,  sinus 
Median  part  of  upper  surface  of 

basi  occipital 
Highest  curved  line 
Superior  curved  line 
Inferior  curved  line 

Sphenoid 

Pterygoid  ridge 
Optic  groove 
Ethmoidal  crest 
Spinous  process 
Internal  pterygoid  plate 

External  pterygoid  plate 

A^idian  canal 
Pituitary  fossa 
Cavernous  groove 
Sphenoidal  turbinal  bones 
Hamular  process 
Pterygo-palatine  canal 
Olivary  eminence 
Sphenoidal  fissure 

Temporal  Bone 

Aqueduct  of  Fallopius 

Hiatus  Fallopii 

Vaginal  process  of  tympanic  bone 

Digastric  fossa 

Impression  for  Gasserian  ganglion 

Eminence    for   sup.    semicircular 

canal 
Fossa  sigmoid ea 
Glaserian  fissure 
Glenoid  cavity 
Eustachian  tube 

Ethmoid 

Lateral  mass 
Os  planum 
Unciform  process 


xu 


GLOSSARY 


B.N. A.  Terminology. 

Os  lacrimale 

Hamulus  lacrimalis 
Crista  lacrimalis  posterior 

Os  nasale 

Sulcus  ethmoidalis 

Maxilla 

Facies  anterior 
Facies  infra-temporalis 
Sinus  maxillaris 
Processus  frontalis 
Processus  zygomaticus 
Canales  alveolares 
Canalis  naso-lacrimalis 
Os  incisivum 
Foramen  incisivum 

Os  palatinum 

Pars  perpendicularis 
Crista  conchalis 
Crista  ethmoidalis 
Pars  horizontalis 

Os  zygomaticum 

Processus  temporalis 
Processus  fronto-sphenoidalis 
Foramen  zygomatico-orbitale 
Foramen  zygomatico-faciale 

Mandibula 

Spina  mentalis 
Linea  obliqua 
Linea  mylohyoidea 
Incisura  niandibulse 
Foramen  mandibulare 
Canalis  mandibulse 
Protuberantia  mentalis 


Old  Terminology. 

Lachrymal  Bone 

Hamular  process 
Lachrymal  crest 

Nasal  Bone 

Groove  for  nasal  nerve 

Superior  Maxillary  Bone 

Facial  or  external  surface 
Zygomatic  surface 
Antrum  of  Highmore 
Nasal  process 
Malar  process 
Posterior  dental  canals 
Lacrimal  groove 
Premaxilla 
Anterior  palatine  foramen 

Palate  Bone 

Vertical  plate 
Inferior  turbinate  crest 
Superior  turbinate  crest 
Horizontal  plate 

Malar  Bone 

Zygomatic  process 
Frontal  process 
Tempora-malar  canal 
Malar  foramen 

Inferior  Maxillary  Bone 

Genial  tubercle  or  spine 
External  oblique  line 
Interna]  oblique  line 
Sigmoid  notch 
Inferior  dental  foramen 
Inferior  dental  canal 
Mental  process 


The  Skull  as  a  Whole. 


Ossa  suturarum 

Foveolse  granulares  (Pacchioni) 

Fossa  pterygo-palatina 

Canalis  pterygo-palatinus 

Foramen  lacerum 

Choanae 

Fissura  orbitalis  superior 

Fissura  orbitalis  inferior 


Wormian  bones 
Pacchionian  depressions 
Spheno-maxillary  fossa 
Posterior  palatine  canal 
Foramen  lacerum  medium 
Posterior  nares 
Sphenoidal  fissure 
Spheno-maxillary  fissure 


GLOSSARY 


Xlll 


Upper  Extremity. 

B.N. A.  Terminology.  Old  Termlnology. 

Clavicula  Clavicle 


\ 


Tuberositas  coracoidea 
Tuberositas  costalis 

Scapula 

Incisura  scapularis 
Angulus  lateralis 
Angulus  medialis 

Humerus 

Sulcus  intertubercularis 
Crista  tuberculi  majoris 
Crista  tuberculi  minoris 
Facies  anterior  medialis 
Facies  anterior  lateralis 
Margo  medialis 
Margo  lateralis 
Sulcus  nervi  radialis 
Capitulum 

Epicondylus  medialis 
Epicondylus  lateralis 

Ulna 

Incisura  semilunaris 
Incisura  radialis 
Crista  interossea 
Facies  dorsalis 
Facies  volaris 
Facies  medialis 
Margo  dorsalis 
Margo  volaris 

Radius 

Tuberositas  radii 
Incisura  ulnaris 
Crista  interossea 
Facies  dorsalis 
Facies  volaris 
Facies  lateralis 
Margo  dorsalis 
Margo  volaris 

Carpus 

Os  naviculare 

Os  lunatum 

Os  triquetrum 

Os  multangulum  majus 

Os  multangulum  minus 

Os  capitatum 

Os  hamatum 


Impression  for  conoid  ligament 
Impression  for  rhomboid  ligament 

Scapula 

Supra-scapular  notch 
Anterior  or  lateral  angle 
Superior  angle 

Humerus 

Bicipital  groove 

External  lip 

Internal  lip 
Internal  surface 
External  surface 
Internal  border 
External  border 
Musculo-spiral  groove 
Capitellum 
Internal  condyle 
External  condyle 

Ulna 

Greater  sigmoid  cavity 
Lesser  sigmoid  cavity 
External  or  interosseous  border 
Posterior  surface 
Anterior  surface 
Internal  surface 
Posterior  border 
Anterior  border 

Radius 

Bicipital  tuberosity 

Sigmoid  cavity 

Internal  or  interosseous  border 

Posterior  surface 

Anterior  surface 

External  surface 

Posterior  border 

Anterior  border 

Carpus 
Scaphoid 
Semilunar 
Cuneiform 
Trapezium 
Trapezoid 
Os  magnum 
Unciform 


XIV 


GLOSSARY 


Lower  Extremity. 


B.N. A.   Terminology. 

Os  coxse 

Linea  glutsea  anterior 
Linea  glutaea  posterior 
Linea  terminalis 
Spina  ischiadica 
Incisura  ischiadica  major 
Incisura  ischiadica  minor 
Tuberculum  pubicum 
Ramus  inferior  oss.  pubis 
Ramus  superior  oss.  pubis 
Ramus  superior  ossis  ischii 
Ramus  inferior  oss.  ischii 
Pecten  ossis  pubis 
Facies  symphyseos 

Pelvis 

Pelvis  major 

Pelvis  minor 

Apertura  pelvis  minoris  superior 

Apertura  pelvis  minoris  inferior 

Femur 

Fossa  trochanterica 
Linea  intertrochanterica 
Crista  intertrochanterica 
Condylus  medialis 
Condylus  lateralis 
Epicondylus  medialis 
Epicondylus  lateralis 

Tibia 

Condylus  medialis 
Condylus  lateralis 
Eminentia  intercondyloidea 
Tuberositas  tibise 
Malleolus  medialis 

Fibula 

Malleolus  lateralis 


Old  Terminology, 

Innominate  Bone 

Middle  curved  line 

Superior  curved  line 

Margin  of  inlet  of  true  pelvis 

Spine  of  the  ischium 

Great  sacro-sciatic  notch 

Lesser  sacro-sciatic  notch 

Spine  of  pubis 

Descending  ramus  of  pubis 

Ascending  ramus  of  pubis 

Body  of  ischium 

Ramus  of  ischium 

Pubic  part  of  ilio-pectineal  line 

Symphysis  pubis 

Pelvis 

False  pelvis 
True  pelvis 
Pelvic  inlet 
Pelvic  outlet 

Femur 

Digital  fossa 

Spiral  line 

Post,  intertrochanteric  line 

Inner  condyle 

Outer  condyle 

Inner  tuberosity 

Outer  tuberosity 

Tibia 

Internal  tuberosity 
External  tuberosity 
Spine 
Tubercle 
Internal  malleolus 

Fibula 

External  malleolus 


Bones  of  the  Foot. 


Talus 
Calcaneus 

Tuber  calcanei 

Processus  medialis  tuberis  calcanei 

Processus  lateralis  tuberis  calcanei 

Os  cuneiforme  primum 

Os  cuneiforme  secundum 

Os  cuneiforme  tertium 


Astragalus 
Os  calcis 

Tuberosity  of 

Inner 

Outer 
Inner  cuneiform 
Middle  cuneiform 
Outer  cuneiform 


GLOSSARY 


XV 


THE    LIGAMENTS. 
Ligaments  of  the  Spine. 


B.N. A.  Terminology. 

Lig.  longitudinale  anterius 

Lig.  longitudinale  posteiius 

Lig.  flava 

Membrana  tectoria 

Articulatio  atlanto-epistrophica 

Lig.  alaria 

Lig.  apicis  dentis 


Old  Terminology. 

Anterior  common  ligament 
Posterior  common  ligament 
Ligamenta  subflava 
Posterior  occipito-axial  ligament 
Joint  between  the  atlas  and  the  axis 
Odontoid  or  check  ligaments 
Suspensory  ligament 


The  Ribs. 

Lig.  capituli  costfe  radiatum 
Lig.  sterno-costale  interarticulare 
Lig.  sterno-costalia  radiata 
Lig.  costoxiphoidea 


Anterior  costo-vertebral  or  stellate 
ligament 

Interarticular  chondro-sternal  liga- 
ment 

Anterior  and  posterior  chondro- 
sternal  ligament 

Chondro-xiphoid  ligaments 


Lig.  temporo-mandibulare 
Lig.  spheno-mandibulare 
Lig.  stylo-mandibulare 


The  Jaw. 


External  lateral  ligament  of  the  jaw 
Internal  lateral  ligament  of  the  jaw 
Stylo-maxillary  ligament 


Upper  Extremity. 


Lig.  costo-claviculare 

Labrum  glenoidale 

Articulatio  radio-ulnaris  proximalis 

Lig.  collaterale  ulnare 

Lig.  collaterale  radiale 

Lig.  annulare  radii 

Chorda  obliqua 

Articulatio  radio-ulnaris  distalis 

Discus  articularis 

Recessus  sacciformis 

Lig.  radio-carpeum  volare 

Lig.  radio-carpeum  dorsale 

Lig.  collaterale  carpi  ulnare 

VOL.  II — b 


Rhomboid  ligament 

Glenoid  ligament 

Superior  radio-ulnar  joint 

Internal  lateral  ligament  of  elbow- 
joint 

External  lateral  ligament 

Orbicular  ligament 

Oblique  ligament  of  ulna 

Inferior  radio-ulnar  joint 

Triangular  fibro-cartilage 

Membrana  sacciformis 

Anterior  ligament  of  the  radio- 
carpal joint 

Posterior  ligament  of  the  radio- 
carpal joint 

Internal  lateral  ligament  of  the 
wrist  joint 


XVI 


GLOSSARY 


B.N. A.  Terminology 
Lig.  collaterale  carpi  radiale 


Old  Terminology. 

External    lateral    ligament    of   the 

wrist  joint 
Carpal  joints 

Palmar  ligaments  of  the  metacarpo- 
phalangeal joints 
Lig.     capitulorum     (oss.     metacar-       Transverse  metacarpal  ligament 

palium)  transversa 
Lig.  collateralia  Lateral  phalangeal  ligaments 


Articulationes  intercarpae 
Lig.  accessoria  volaria 


The  Lower  Extremity. 


Lig.  arcuatum 

Lig.  sacro-tuberosum 

Processus  falciformis 
Lig.  sacro-spinosum 
Labrum  glenoidale 
Zona  orbicularis 
Ligamentum  iliofemorale 
Lig.  ischio-capsulare 
Lig.  pubo-capsulare 
Lig.  popliteum  obliquum 
Lig.  collaterale  fibulare 
Lig.  collaterale  tibiale 
Lig.  popliteum  arcuatum 
Meniscus  lateralis 
Meniscus  medialis 
Plica  synovialis  patellaris 
Plicae  alares 

Articulatio  tibio-fibularis 
Lig.  capituli  fibulae 

Syndesmosis  tibio-fibularis 

Lig.  deltoideum 

Lig.  talo-fibulare  anterius 

Lig.  talo-fibulare  posterius 

Lig.  calcaneo-fibulare 

Lig.  talo-calcaneum  laterale 

Lig.  talo-calcaneum  mediale 

Lig.  calcaneo-naviculare  plantare 

Lig.  talo-naviculare 

Pars  calcaneo-navicularis  "j  lig. 

y  bifur- 
Pars  calcaneo-cuboidea     j  catum 


Subpubic  ligament 

Great  sacro-sciatic  ligament 
Falciform  process 

Small  sacro-sciatic  ligament 

Cotyloid  ligament 

Zonular  band 

Y-shaped  ligament 

Ischio-capsular  band 

Pubo-femoral  ligament 

Ligament  of  Winslow 

Long  external  lateral  ligament 

Internal  lateral  ligament 

Arcuate  popliteal  ligament 

P^xternal  semilunar  cartilage 

Internal  semilunar  cartilage 

Lig.  mucosum 

Ligamenta  alaria 

Superior  tibio-fibular  articulation 

Anterior     and     posterior     superior 
tibio-fibular  ligaments 

Inferior  tibio-fibular  articulation 

Internal  lateral  ligament  of  ankle 

Anterior     fasciculus      of     external 
lateral  ligament 

Posterior     fasciculus     of     external 
lateral  ligament 

Middle  fasciculus  of  external  lateral 
ligament 

External  calcaneo-astragaloid   liga- 
ment 

Internal   calcaneo-astragaloid    liga- 
ment 

Inferior  calcaneo-navicular  ligament 

Astragalo-scaphoid  ligament 

Superior     calcaneo- scaphoid     liga- 
ment 

Internal  calcaneo-cuboid  ligament 


GLOSSARY 


xvii 


THE  MUSCLES. 

Muscles  of  the  Back. 
Superficial. 


B.N. A.  Terminology. 
Levator  scapulas 


Old  Terminology. 
Levator  anguli  scapulee 


Serratus  anterior 


Muscles  of  the  Chest. 

Serratus  ma^nus 


Muscles  of  Upper  Extremity. 


Biceps  brachii 

Lacertus  fibrosus 
Brachialis 
Triceps  brachii 

Caput  mediale 

Caput  laterale 
Pronator  teres 

Caput  ulnare 
Brachio-radialis 
Supinator 

Extensor  carpi  radialis  longus 
Extensor  carpi  radialis  brevis 
Extensor  indicis  proprius 
Extensor  digiti  quinti  proprius 
Abductor  pollicis  longus 
Abductor  pollicis  brevis 
Extensor  pollicis  brevis 
Extensor  pollicis  longus 
Lig.  carpi  transversum 
Lig.  carpi  dorsale 


Biceps 

Bicipital  fascia 
Brachialis  anticus 
Triceps 

Inner  head 

Outer  head 
Pronator  radii  teres 

Coronoid  head 
Supinator  longus 
Supinator  brevis 
Extensor  carpi  radialis  longior 
Extensor  carpi  radialis  brevior 
Extensor  indicis 
Extensor  minimi  digiti 
Extensor  ossis  metacarpi  pollicis 
Abductor  pollicis 
Extensor  primi  internodii  pollicis 
Extensor  secundi  internodii  pollicis 
Anterior  annular  ligament 
Posterior  annular  ligament 


Muscles  of  Lower  Extremity. 


Tensor  fascise  latoe 

Canalis  adductorius  (Hunteri) 

Trigonum  femorale    (fossa    Scarpse 

major) 
Canalis  femoralis 
Annulus  femoralis 
M.  quadriceps  femoris — 

Rectus  femoris 

Vastus  lateralis 

Vastus  intermedius 

Vastus  medialis 

M.  articularis  genu 
Tibialis  anterior 


Tensor  fascise  femoris 
Hunter's  canal 
Scarpa's  triangle 

Crural  canal 
Crural  ring 
Quadriceps — 

Rectus  femoris 

Vastus  externus 

Crureus 

Vastus  internus 

Subcrureus 
Tibialis  anticus 


XVlll 


GLOSSARY 


B.N. A.  Terminology, 

Tendo  calcaneus 
Tibialis  posterior 
Quadratus  plantae 
Lig.  transversum  cruris 
Lig.  cruciatum  cruris 
Lig.  laciniatum 
Retinaculum    musculorum 


nreorum  superius 
Retinaculum    musculorum 
naeorum  inferius 


pero- 


pero- 


Old  Terminology. 

Tendo  Achillis 

Tibialis  posticus 

Accessorius 

Upper  anterior  annular  ligament 

Lower  anterior  annular  ligament 

Internal  annular  ligament 

External  annular  ligament 


Axial  Muscles. 
Muscles  of  the  Back. 


Serratus  posterior  superior 
Serratus  posterior  inferior 
Splenius  cervicis 
Sacro-spinalis 
Ilio-costalis— 

Lumborum 

Dorsi 

Cervicis 
Longissimus — 

Dorsi 

Cervicis 

Capitis 
Spinalis — 

Dorsi 

Cervicis 

Capitis 
Semispinalis — 

Dorsi 

Cervicis 

Capitis 
Multifidus 


Serratus  posticus  superior 
Serratus  posticus  inferior 
Splenius  colli 
Erector  spinse 
Ilio-costalis — 

Sacro-lumbalis 

Accessorius 

Cervicalis  ascendens 
Longissimus — 

Dorsi 

Transversalis  cervicis 

Trachelo-mastoid 
Spinalis — 

Dorsi 

Colli 

Capitis 
Semispinalis — 

Dorsi 

Colli 

Complexus 
Multifidus  spin£e 


Muscles  of  Head  and  Neck. 


Epicranius 
Galea  aponeurotica 
Procerus 

Pars  transversa  (nasalis) 
Pars  alaris  (nasalis) 
Auricularis  anterior 
Auricularis  posterior 
Auricularis  superior 
Orbicularis  oculi 
Pars  lacrimalis 


Occipito-frontalis 
Epicranial  aponeurosis 
Pyramidalis  nasi 
Compressor  naris 
Dilatores  naris 
Attrahens  aurem 
Retrahens  aurem 
Attollens  aurem 
Orbicularis  palpebrarum 
Tensor  tarsi 


GLOSSARY 


XIX 


B.N. A.  Terminology. 
Triangularis 
Quadratus  labii  superioris — 

Caput  zygomaticum 

Caput  infraorbitale 

Caput  angulare 
Zygomaticus 
Caninus 

Quadratus  labii  inferioris 
Mentalis 
Platysma 
Sterno-thyreoid 
Tliyreo-hyoid 


Old  Terminology. 
Depressor  anguli  oris 

Zygomaticus  minor 

Levator  labii  superioris 

Levator  labii  superioris  alceque  nasi 

Zygomaticus  major 

Levator  anguli  oris 

Depressor  labii  inferioris 

Levator  menti 

Platysma  myoides 

Sterno-thyroid 

Thyro-hyoid 


Muscles  and  Fascia  of  the  Orbit. 

Fascia  bulbi  Capsule  of  Tenon 

Septum  orbitale  Palpebral  ligaments 

Rectus  lateralis  Rectus  externus 

Rectus  medialis  Rectus  internus 

Muscles  of  the  Tongue. 


Genio-glossus 
Longitudinalis  superior 
Longitudinalis  inferior 
Transversus  linguoe 
Verticalis  linguae 


Genio-hyo-glossus 
Superior  lingualis 
Inferior  lingualis 
Transverse  fibres 
Vertical  fibres 


Pharyngo-palatinus 

INI.  uvulae 

Levator  veli  palatini 
Tensor  veli  palatini 
Glosso-palatinus 


Muscles  of  the  Pharynx. 

Palato-pharyngeus 
Azygos  uvulae 
Levator  palati 
Tensor  palati 
Palato-elossus 


Deep  Lateral  Muscles  of  Neck. 

Scalenus  anterior  Scalenus  anticus 

Scalenus  posterior  Scalenus  posticus 

Longus  capitis  Rectus  capitis  anticus  major 

Rectus  capitis  anterior  Rectus  capitis  anticus  minor 

Muscles  of  Thorax. 


Transversus  thoracis 

Triangularis  sterni 

Diaphragma  pars  lumbalis 
Crus  mediale          "j 
Crus  intermedium   - 
Crus  laterale 

Diaphragm,  lumbar  part — 

Crura   and  origins   from  arcuate 
ligaments 

Arcus    lumbo  -  costalis 

medialis 

Ligamentum  arcuatum  internum 

(Halleri) 

Arcus    lumbo  -  costalis 

lateralis 

Ligamentum  arcuatum  externum 

(Halleri) 

XX 


GLOSSARY 


Muscles  of  the  Abdomen. 


B.N. A,  Terminology. 

Ligamentum  inguinale  (Pouparti) 
Ligamentum  lacunare  (Gimbernati) 
Fibrse  intercrurales 
Ligamentum      inguinale      reflexum 

(Collesi) 
Annulus  inguinalis  subcutaneus 

Crus  superius 

Crus  infehus 
Falx  aponeurotica  inguinalis 
M.  transversus  abdominis 
Linea  semicircularis  (Douglasi) 
Annulus  inguinalis  abdominalis 


Old  Terminology. 

Poupart's  ligament 
Gimbernat's  ligament 
Intercolumnar  fibres 
Triangular  fascia 

External  abdominal  ring 

Internal  pillar 

External  pillar 
Conjoined  tendon 
Transversalis  muscle 
Fold  of  Douglas 
Internal  abdominal  ring 


Perineum  and  Pelvis. 


Transversus  perinei  superficialis 
M.  sphincter  urethrae  membranacese 
Diaphragma  urogenitale 

Fascia    diaphragmatis    urogenitalis 

superior 
Fascia    diaphragmatis    urogenitalis 

inferior 
Arcus  tendineus  fasciae  pelvis 
Ligamenta  puboprostatica 

Fascia  diaphragmatis  pelvis  superior 
Fascia  diaphragmatis  pelvis  inferior 


Transversus  perinei 
Compressor  urethrae 
Deep  transverse  muscle  and  sphinc- 
ter urethrse 
Deep  layer  of  triangular  ligament 

Superficial   layer   of  the   triangular 

ligament 
White  line  of  pelvis 
Anterior  and  lateral  true  ligaments 

of  bladder 
Visceral  layer  of  pelvic  fascia 
Anal  fascia 


THE    NERVOUS    SYSTEM. 


Spinal  Cord. 


Fasciculus  anterior  proprius  (Flech- 
sig) 

Fasciculus  lateralis  proprius 

Nucleus  dorsalis 

Pars  thoracalis 

Sulcus  intermedius  posterior 

Columnse  anteriores,  etc. 

Fasciculus  cerebro-spinalis  anterior 

Fasciculus  cerebro-spinalis  lateralis 
(pyramidalis) 

Fasciculus  cerebello-spinalis 

Fasciculus  antero- lateralis  super- 
ficialis 


Anterior  ground  or  basis  bundle 

Lateral  ground  bundle 
Clarke's  column 
Dorsal  part  of  spinal  cord 
Paramedian  furrow 
Anterior  grey  column 
Direct  pyramidal  tract 
Crossed  pyramidal  tract 

Direct  cerebellar  tract 
Gowers'  tract 


GLOSSARY 


XXI 


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XXll 


GLOSSARY 


Brain. 


B.N. A.  Terminology. 


Ehombenceplialon 

Eminentia  medialis 

Ala  cinerea 

Ala  acustica 

Nucleus  nervi  abducentis 

Nuclei  n.  acustici 

Fasciculus  longitudinalis  medialis 

Corpus  trapezoideum 

Incisura  cerebelli  anterior 

Incisura  cerebelli  posterior 

Sulcus  horizontalis  cerebelli 

Lobulus  centralis 

Folium  vermis 

Tuber  vermis 

Lobulus  quadrangularis 

Brachium  conjunctivum  cerebelli 

Lobulus  semilunaris  superior 

Lobulus  semilunaris  inferior 

Cerebrum 

Pedunculus  cerebri 
Colliculus  superior 
Colliculus  inferior 
Aqueductus  cerebri 

Foramen  interventriculare 
Hypothalamus 
Sulcus  hypothalamicus 
Massa  intermedia 
Fasciculus  thalamo-mammillaris 
Pars  opercularis 
Thalamus 
Pallium 
Gyri  transitivi 
Fissura  cerebri  lateralis 
Gyrus  temporalis  superior 
Gyrus  temporalis  medius 
Gyrus  temporalis  inferior 
Sulcus  centralis  (Rolandi) 
Sulcus  temporalis  superior 
-    Sulcus  temporalis  medius 
Sulcus  circularis 
Sulcus  temporalis  inferior 
Gyrus  fusiformis 
Sulcus  interparietalis 
Sulcus  corporis  callosi 
Sulcus  cinguli 
Fissura  hippocampi 
Gvrus  cinguli 


Old  Terminology. 

Eminentia  teres 

Trigonum  vagi 

Trigonum  acusticum 

Nucleus  of  6th  nerve 

Auditory  nucleus 

Posterior  longitudinal  bundle 

Corpus  trapezoides 

Semilunar  notch  (of  cerebellum) 

Marsupial  notch 

Great  horizontal  fissure 

Lobus  centralis 

Folium  cacuminis 

Tuber  valvulae 

Quadrate  lobule 

Superior  cerebellar  peduncle 

Postero-superior  lobule 

Postero-inferior  lobule 

Crus  cerebri 

Anterior  corpus  quadrigeminum 
Posterior  corpus  quadrigeminum 
Iter  e  tertio  ad  quartum  ventri- 

culum,  or  aqued.  of  Sylvius 
Foramen  of  Monro 
Subthalmic  region 
Sulcus  of  Monro 
Middle  commissure 
Bundle  of  Vicq  d'Azyr 
Pars  basilaris 
Optic  thalamus 
Cortex  cerebri 
Annectant  gyri 
Fissure  of  Sylvius 
First  temporal  gyrus 
Second  temporal  gyrus 
Third  temporal  gyrus 
Fissure  of  Rolando 
Parallel  sulcus 
Second  temporal  sulcus 
Limiting  sulcus  of  Reil 
Occipito-temporal  sulcus 
Occipito-temporal  convolution 
Intraparietal  sulcus 
Callosal  sulcus 
Calloso-marginal  fissure 
Dentate  fissure 
Callosal  convolution 


GLOSSARY 


XXlll 


B.N. A.  Terminology. 
Stria  terminalis 
Trigonum  collaterale 
Hippocampus 
Digitationes  hippocampi 
Fascia  dentata  hippocampi 
Cohimna  fornicis 
Septum  peUucidum 
Inferior  cornu 
Commissura  hippocampi 
Nucleus  lentiformis 
Pars  frontalis  capsuk^e  internje 
Pars  occipitalis  capsular  internae 
Radiatio  occipito-thalamica 
Radiatio  corporis  callosi 

Pars  frontalis 

Pars  occipitalis 


Old  Termlnology. 
Taenia  semicircularis 
Trigonum  ventriculi 
Hippocampus  major 
Pes  hippocampi 
Gyrus  dentatus 
Anterior  pillar  of  fornix 
Septum  lucidum 

Descending  horn  of  lateral  ventricle 
Lyra 

Lenticular  nucleus 
Anterior  limb  (of  internal  capsule) 
Posteriorlimb (of  internal  capsule) 
Optic  radiation 
Radiation  of  corpus  callosum 

Forceps  minor 

Forceps  major 


Membranes  of  Brain. 


Cisterna  cerebello-medullaris 
Cisterna  interpeduncularis 
Granulationes  arachnoideales 
Tela  chorioidea  ventriculi  tertii 
Tela  chorioidea  ventriculi  quarti 


Cisterna  magna 
Cisterna  basalis 
Pacchionian  bodies 
Velum  interpositum 
Tela  choroidea  inferior 


Cerebral  Nerves. 


N.  oculomotorius 
N.  trochlearis 
N.  trigeminus 

Ganglion  semilunare  (Gasseri) 

N.  naso-ciliaris 

N.  maxillaris 

N.  meningeus  (medius) 

N,  zygomaticus 

Rami  alveolares  superiores  pos- 
teriores 

Rami  alveolares  superiores  medii 

Rami    alveolares   superiores    an- 
teriores 

Ganglion  spheno-palatinum 

N.  palatinus  medius 

N.  mandibularis 

Nervus  spinosus 

N.  alveolaris  inferior 
N.  abducens 
N.  facialis 
N.  intermedius 
■N.  acusticus 


Third  nerve 

Fourth  nerve 

Fifth  nerve 

Gasserian  ganglion 
Nasal  nerve 

Superior  maxillary  nerve 
Recurrent  meningeal  nerve 
Temporo-malar  nerve 
Posterior  superior  dental 

Middle  superior  dental 
Anterior  superior  dental 

Meckel's  ganglion 
External  palatine  nerve 
Inferior  maxillary  nerve 
Recurrent  nerve 
Inferior  dental 

Sixth  nerve 

Seventh  nerve 

Pars  intermedia  of  Wrisberg 

Eighth  or  auditory  nerve 


XXIV 


GLOSSARY 


B.N. A.  Terminology. 

Ganglion  superius 
N,  recurrens 
Ganglion  jugulare 
Ganglion  nodosum 
Plexus  oesophageus  anterior    1 
Plexus  oesophageus  posterior  J 
Nervus  accessorius 
Ramus  internus 


Ramus  externus 


Old  Terminology. 

Jugular  ganglion  of  9th  nerve 

Recurrent  laryngeal  nerve 

Ganglion  of  root    ^    ^ 

r^        T         r  ^       1    /-or  vagus 

Ganglion  or  trunk  j  '=' 

Plexus  gulae 

Spinal  accessory 

Accessory    portion     of    spinal 

accessory  nerve 
Spinal  portion 


Spinal  Nerves. 


Rami  posteriores 

Rami  anteriores 

N.  cutaneus  colli 

Nn.  supraclaviculares  anteriores 

Nn.  supraclaviculares  medii 

Nn.  supraclaviculares  posteriores 

N.  dorsalis  scapulae 

Nn.  intercosto-brachiales 

N.  thoracalis  longus 

N.  thoraco-dorsalis 

N.  cutaneus  brachii  medialis 

N.  cutaneus  brachii  lateralis 

Fasciculus  lateralis 
Fasciculus  medialis 
N.  cutaneus  antibrachii  lateralis 

N.  cutaneus  antibrachii  medialis 

Ramus  volaris 

Ramus  ulnaris 
N.  cutaneus  antibrachii  dorsalis 

N.  axillaris 

N.  interosseus  volaris 

Ramus  palmaris  N.  median! 

Nn.  digitales  volares  proprii 

Ramus  dorsalis  manus 

Ramus  cutaneus  palmaris 

N.  radialis 

N.  cutaneus  brachii  posterior 

N.  cutaneus  antibrachii  dorsalis 


Posterior  primary  divisions 
Anterior  primary  divisions 
Superficial  cervical  nerve 
Suprasternal  nerves 
Supraclavicular  nerves 
Supra-acromial  nerves 
Nerve  to  the  rhomboids 
Intercosto-humeral  nerve 
Nerve  of  Bell 
Long  subscapular  nerve 
Lesser  internal  cutaneous  nerve 
Cutaneous    branch     of    circumflex 

nerve 
Outer  cord  (of  plexus) 
Inner  cord 
Cutaneous  branch  of  musculo-cuta- 

neous  nerve 
Internal  cutaneous  nerve 
Anterior  branch 
Posterior  branch 
External  cutaneous  branch  of  mus- 

culo-spiral 
Circumflex  nerve 
Anterior  interosseous 
Palmar   cutaneous    branch    of    the 

median  nerve 
Collateral   palmar  digital  branches 

of  median  nerve 
Dorsal   cutaneous  branch    of  ulnar 

nerve 
Palmar  cutaneous  branch  of  ulnar 

nerve 
Musculo-spiral  nerve 

Internal   cutaneous   branch   of 

musculo-spiral  nerve 
External  cutaneous  branches  of 
musculo-spiral  nerve 


GLOSSARY 


XXV 


B.N. A.   Terminology. 

Ramus  superficialis 

N.  interosseus  dorsalis 
Nn.  digitales  dorsales 
N.  ilio-hypogastricus 

Ramus  cutaneus  lateralis 

Ramus  cutaneus  anterior 

N.  genito-femoralis 

N.  lumbo-inguinalis 

N.  spermaticus  externus 

N.  cutaneus  femoris  lateralis 
N.  femoralis 
N.  saphenus 

Ramus  infrapatellaris 

N.  ischiadicus 

N.  peronasus  communis 

Ramus     anastomoticus     pero- 
nasus 

N,  peronaeus  superficialis 

N.  peronseus  profundus 
N.  tibialis 

N.  cutaneus  sura  medialis 
N.  suralis 

N.  plantaris  medialis 
N.  plantaris  lateralis 
N.  pudendus 


Old  Terminology. 

Radial  nerve 

Posterior  interosseous  nerve 
Dorsal  digital  nerves 
Ilio-hypogastric  nerve 

Iliac  branch  of  ilio-hypogastric 

nerve 
Hypogastric    branch    of    ilio- 
hypogastric nerve 
Genito-crural  nerve 

Crural  branch  of  genito-crural 

nerve 
Genital  branch  of  genito-crural 
nerve 
External  cutaneous  nerve 
Anterior  crural  nerve 
Long  saphenous  nerve 

Patellar  branch  of  long  saph- 
enous nerve 
Great  sciatic  nerve 
External  popliteal  nerve 

Nervus  communicans  fibularis 

Musculo-cutaneous  nerve 

Anterior  tibial  nerve 
Internal  popliteal  nerve 

Nervus  communicans  tibialis 
Short  saphenous  nerve 
Internal  plantar 
External  plantar 
Pudic  nerve 


THE    HEART    AND    BLOOD-VESSELS. 


Heart. 


Atrium 

Auricula  cordis 
Incisura  cordis 
TrabeculcC  carneae 
Tuberculum  intervenosum 
Sulcus  longitudinalis  anterior 
Sulcus  coronarius 
Limbus  fossae  ovalis 
Valvula  venae  cavee 
Valvula  sinus  coronarii 


Auricle 

Auricular  appendix 

Notch  at  apex  of  heart 

Columnas  carneL'e 

Intervenous  tubercle  of  Lower 

Anterior  interventricular  groove 

Auriculo-ventricular  groove 

Annulus  ovalis 

Eustachian  valve 

Valve  of  Thebesius 


XXVI 


GLOSSARY 


Arteries. 


B.N. A.  Terminology. 
Sinus  aortae 
A.  profunda  linguae 
A.  maxillaris  externa 
A.  alveolaris  inferior 
Ramus  meningeus  accessorius 
A.  buccinatoria 

A.  alveolaris  superior  posterior 
Aa.  alveolares  superiores  anteriores 
Ramus  carotico-tympanicus 
A.  chorioidea 
A.  auditiva  interna 
Rami  ad  pontem 

A.  pericardiaco-phrenica 
Rami  intercostales 
Truncus  thyreo-cervicalis 
A.  transversa  scapulge 
A.  intercostalis  suprema 
A.  transversa  colli 
A.  thoracalis  suprema 
A.  thoraco-acromialis 
A.  thoracalis  lateralis 
A.  circumflexa  scapulae 
A.  profunda  brachii 
A.  collateralis  radialis 

A.  collateralis  ulnaris  superior 
A,  collateralis  ulnaris  inferior 
Ramus  carpeus  volaris 
Ramus  carpeus  dorsalis 
Aa.  metacarpese  dorsales 
A.  volaris  indicis  radialis 
Arcus  volaris  superficialis 
Arcus  volaris  profundus 
A.  interossea  dorsalis 
A.  interossea  recurrens 

A.  interossea  volaris 

Ramus  carpeus  dorsalis 

Ramus  carpeus  volaris 

Aa.  digitales  volares  communes 

Aa.  digitales  volares  propriae 

Arteriae  intestinales 

A.  suprarenalis  media 
A.  hypogastrica 
A.  umbilicalis 
A.  pudenda  interna 
A.  epigastrica  inferior 


Old  Terminology. 

Sinuses  of  Valsalva 

Ranine  artery 

Facial  artery 

Inferior  dental  artery 

Small  meningeal  artery 

Buccal  artery 

Posterior  dental  artery 

Anterior  superior  dental  arteries 

Tympanic  branch  of  int.  carotid 

Anterior  choroidal  artery 

Auditory  artery 

Transverse    arteries     (branches    of 
Basilar  artery) 

Arteria  comes  nervi  phrenici 

Anterior  intercostal  arteries 

Thyroid  axis 

Suprascapular  artery 

Superior  intercostal 

Transversalis  colli 

Superior  thoracic  artery 

Acromio-thoracic  artery 

Long  thoracic  artery 

Dorsalis  scapulae 

Superior  profunda 

Anterior  branch   of    superior    pro- 
funda 

Inferior  profunda 

Anastomotica  magna 

Anterior  radial  carpal 

Posterior  radial  carpal 

Dorsal  interosseous  arteries 

Radialis  indicis 

Superficial  palmar  arch 

Deep  palmar  arch 

Posterior  interosseous  artery 

Posterior    interosseous    recurrent 
artery 

Anterior  interosseous  artery 

Posterior  ulnar  carpal 

Anterior  ulnar  carpal 

Palmar  digital  arteries 

Collateral  digital  arteries 

Intestinal  branches  of  sup.   mesen- 
teric 

Middle  capsular  artery 

Internal  iliac  artery 

Obliterated  hypogastric 

Internal  pudic  artery 

Deep  epigastric  artery 


GLOSSARY 


XXVll 


B.N, A.   Terminology. 

A.  spermatica  externa 
Aa.  pudendte  externce 

A.  circumflexa  femoris  medialis 

A.  circumflexa  femoris  lateralis 

A.  genu  suprema 

A.  genu  superior  lateralis 

A.  genu  superior  medialis 

A.  genu  media 

A.  genu  inferior  lateralis 

A.  genu  inferior  medialis 

A.  malleolaris  anterior  lateralis 

A.  malleolaris  anterior  medialis 

A.  peroncea 

Ramus  perforans 

A.  malleolaris  posterior  lateralis 
A.  malleolaris  posterior  medialis 
Rami  calcanei  laterales 
Rami  calcanei  mediales 
A.  plantaris  medialis 
A.  plantaris  lateralis 
Aa.  metatarseae  plantares 
Aa.  digitales  plantares 


Old  Tekmlnology. 

Cremasteric  artery 

Superficial  and  deep  external  pudic 
arteries 

Internal  circumflex  artery 

External  circumflex  artery 

Anastomotica  magna 

Superior  external  articular  artery 

Superior  internal  articular  artery 

Azygos  articular  artery 

Inferior  external  articular  artery 

Inferior  internal  articular  artery 

External  malleolar  artery 

Internal  malleolar  artery 

Peroneal  artery 

Anterior  peroneal  artery 
Posterior  peroneal  artery 

Internal  malleolar  artery 

External  calcanean  artery 

Internal  calcanean  artery 

Internal  plantar  artery 

External  plantar  artery 

Digital  branches 

Collateral  digital  branches 


Veins. 


V.  cordis  magna 

V.  obliqua  atrii  sinistri 

Lig.  venae  cavse  sinistras 

Vv.  cordis  minimge 

Sinus  transversus 

Confluens  sinuum 

Plexus  basilaris 

Sinus  sagittalis  superior 

Sinus  sagittalis  inferior 

Spheno-parietal  sinus 

V.  cerebri  internae 

V.  cerebri  magna 

V.  terminalis 

V.  basalis 

V.  transversa  scapulae 

V.  thoraco-acromialis 

Vv.  transversae  colli 

V.  thoracalis  lateralis 

V.  azygos 

V.  hemiazygos 

V.  hemiazygos  accessoria 

V.  hypogastrica 

V.  epigastrica  inferior 

V,  saphena  magna 

V.  saphena  parva 


Great  cardiac  vein 
Oblique  vein  of  Marshall 
Vestigial  fold  of  Marshall 
Veins  of  Thebesius 
Lateral  sinus 
Torcular  Herophili 
Basilar  sinus 

Superior  longitudinal  sinus 
Inferior  longitudinal  sinus 
Sinus  alae  parvas 
Veins  of  Galen 
Vena  magna  Galeni 
Vein  of  the  corpus  striatum 
Basilar  vein 
Suprascapular  vein 
Acromio-thoracic  vein 
Transversalis  colli  veins 
Long  thoracic  vein 
Vena  azygos  major 
Vena  azygos  minor  inferior 
Vena  azygos  minor  superior 
Internal  iliac  vein 
Deep  epigastric  vein 
Internal  saphenous  vein 
External  saphenous  vein 


XXV  111 


GLOSSARY 


Lymphatics. 


B.N. A.  Terminology. 
Cisterna  chyli 


Old  Terminology. 
Receptaculum  chyli 


THE   VISCERA. 


Digestive  Apparatus. 


Arcus  glosso-palatinus 

Arcus  pharyngo-palatinus 

Gl.  lingualis  anterior 

Ductus  submaxillaris 

GI.  parotis  accessoria 

Ductus  parotideus  (Stenonis) 

Dentes  prsemolares 

Dens  serotinus 

Papillae  vallatae 

Recessus  pharyngeus 

Tela  submucosa 

Plicae  circulares 

Gl.  intestinales 

Valvula  coli 

Columnge  rectales 

Plicae  transversales  recti 

Valvula  spiralis 

Noduli    lymphatici    aggregati 

(Peyeri) 
Intestinum  jejunum 
Intestinum  ileum 
Noduli    lymphatici    lienales 

(Malpighii) 


Anterior  pillar  of  fauces 
Posterior  pillar  of  fauces 
Gland  of  Nuhn 
Wharton's  duct 
Socia  parotidis 
Stenson's  duct 
Bicuspid  teeth 
Wisdom  tooth 
Circumvallate  papillae 
Lateral  recess  of  pharynx 
Pharyngeal  aponeurosis 
Valvulae  conniventes 
Crypts  of  Lieberkuhn 
Ileo-caecal  valve 
Columns  of  Morgagni 
Valves  of  Houston        " 
Valves  of  Heister 
Peyer's  patches 

Jejunum 

Ileum 

Malpighian  corpuscles 


Respiratory  Apparatus. 


Larynx 

Prominentia  laryngea 

Incisura  thyreoidea  superior 

M.  ary-epiglotticus 

M.  vocalis 

M.  thyreo-epiglotticus 

Appendix  ventriculi  laryngis 

Plica  vocalis 

Plica  ventricularis 

Ligamentum  ventriculare 

Ligamentum  vocale 

Glottis 

Rima  vestibuli 

Cartilago  thyreoidea 


Adam's  apple 

Superior  thyroid  notch 

Aryteno-epiglottidean  muscle 

Internal  thyro-arytenoid  muscle 

Thyro-epiglottidean  muscle 

Laryngeal  sac 

True  vocal  cord 

False  vocal  cord 

Superior  thyro-arytenoid  ligament 

Inferior  thyro-arytenoid  ligament 

Glottis  vera 

Glottis  spuria 

Thyroid  cartilage 


GLOSSARY 


XXIX 


B.N. A.   Terminology. 
Membrana  hyo-thyreoidea 
Cartilage  corniculata  (Santorini) 
Tuberculum  epiglotticum 
Pars  intermembranacea  (rimce 

glottidis) 
Pars     intercartilaginea     (rimse 

glottidis) 
Conus     elasticus     (membrane 

elasticae  larynges) 
Glandula  thyreoidea 
Glomus  caroticum 
Nose 

Concha  nasalis  suprema  (Santorini) 
Concha  nasalis  superior 
Concha  nasalis  media 
Concha  nasalis  inferior 


Old  Terminology. 
Thyro-hyoid  membrane 
Cartilage  of  Santorini 
Cushion  of  epiglottis 
Glottis  vocalis 

Glottis  respiratoria 

Crico-thyroid  membrane 

Thyroid  gland 
Intercarotid  gland  or  body 

Highest  turbinate  bone 
Superior  turbinate  bone 
Middle  turbinate  bone 
Inferior  turbinate  bone 


Urogenital  Apparatus. 


Corpuscula  renis 

Paradidymis 

Appendix  testis 

Ductus  deferens 

Gl.  urethrales 

Glandula  bulbo-urethralis  (Cowperi) 

Folliculi  oophori  vesiculosi 

Cumulus  oophorus 

Tuba  uterina 

Epoophoron 

Appendices  vesiculosi 

Ductus  epoophori  longitudinalis 

Orificium  internum  uteri 

Orificium  externum 

Processus  vaginalis 

Glandula  magna  vestibuli 


Malpighian  corpuscles 

Organ  of  Giraldes 

Hydatid  of  Morgagni  (male) 

Vas  deferens 

Glands  of  Litlre 

Cowper's  gland 

Graafian  follicles 

Discus  proligerus 

Fallopian  tube 

Parovarium 

Hydatids  of  Morgagni  (female) 

Gartner's  duct 

Internal  os  (of  uterus) 

External  os 

Canal  of  Nuck 

Bartholin's  gland 


Peritoneum. 


Bursa  omentalis 
Foramen  epiploicum 
Lig.  phrenico-colicum 
Excavatio    recto-uterina    (cavum 

Douglasi) 
Lig.  gastro-Iienale 


Lesser  peritoneal  sac 
Foramen  of  Winslow 
Costo-colic  ligament 
Pouch  of  Douglas 

Gastro-splenic  omentum 


SENSE    ORGANS. 
The  Eye. 


Sclera 

Lamina  elastica  anterior  (Bowmani) 


Sclerotic  coat 
Bowman's  membrane 


XXX 


GLOSSARY 


B.N. A,  Terminology. 

Lamina    elastica     posterior     (Des- 

cemeti) 
Spatia  anguli  iridis 
Angulus  iridis 
Zonula  ciliaris 
Septum  orbitale 
Fascia  bulbi 

Commissura  palpebrarum  lateralis 
Commissura  palpebrarum  medialis 
Tarsus  superior 
Tarsus  inferior 
Lig.  palpebrale  mediale 
Raphe  palpebralis  lateralis 
Tarsal  glands 


Old  Terminology. 
Descemet's  membrane 

Spaces  of  Fontana 
Irido-corneal  junction 
Zonule  of  Zinn 
Palpebral  ligament 
Capsule  of  Tenon 
External  canthus 
Internal  canthus 
Superior  tarsal  plate 
Inferior  tarsal  plate 
Internal  tarsal  ligament 
External  tarsal  ligament 
Meibomian  glands 


The  Ear. 


Canalis  semicircularis  lateralis 
Ductus  reuniens 
Ductus  cochlearis 
Recessus  sphericus 
Recessus  ellipticus 
Paries  jugularis 
Paries  labyrinthica 

Fenestra  vestibuli 

Fenestra  cochleae 
Paries  mastoidea 

Antrum  tympanicum 
Paries  carotica 
Processus  lateralis 
Processus  anterior 


External  semicircular  canal 
Canalis  reuniens 
Membranous  cochlea 
Fovea  hemispherica 
Fovea  hemi-elliptica 
Floor  of  tympanum 
Inner  wall 

Fenestra  ovalis 

Fenestra  rotunda 
Posterior  wall 

Mastoid  antrum 
Anterior  wall 

Processus  brevis  (of  malleus) 
Processus  gracilis 


MANUAL 

\ 


OF 


PRACTICAL    ANATOMY. 


THORAX. 

'T^HE  dissection  of  the  thorax  is  commenced  on  the  thirteenth 
-*-  day^  after  the  subject  has  been  placed  in  the  dissecting- 
room.  By  that  time  the  upper  hmbs  have  been  detached 
from  the  trunk. 

In  form,  the  thorax  resembles  a  truncated  cone.  Anteriorly 
and  posteriorly  it  is  flattened ;  laterally  it  is  full  and  rounded. 
During  life  the  movements  of  the  thoracic  walls  produce 
alterations  in  the  capacity  of  the  chest  cavity,  and  play  an 
essential  part  in  the  function  of  respiration  ;  these  movements 
the  student  should  study  upon  himself  and  his  friends. 

The  thoracic  cavity  is  bounded  anteriorly  by  the  sternum 
and  costal  cartilages ;  it  is  bounded  posteriorly  by  the  twelve 
thoracic  vertebrae  and  the  intervening  fibro-cartilages,  together 
with  the  portions  of  the  ribs  which  extend  laterally  from  the 
vertebral  column  as  far  as  the  angles  \  the  lateral  boundaries 
are  formed  by  the  bodies  of  the  ribs,  from  their  angles 
posteriorly  to  their  anterior  extremities  anteriorly.  These 
parts  constitute  the  framework  of  the  thorax,  and  can  be 
studied  on  the  skeleton  as  well  as  upon  the  part  before 
the  dissection  is  commenced. 

The  anterior  wall  of  the  thorax  is  shorter  than  the  posterior 
wall  and,  during  expiration,  the  upper  margin  of  the  sternum 

^  Saturdays  and  Sundays  are  not  counted. 
VOL.  II — 1 


THORAX 


lies  opposite  the  fibro-cartilage  between  the  second  and  third 
thoracic  vertebrae,  whilst  the  lower  end  of  the  body  of  the 
sternum  corresponds  in  level  with  the  middle  of  the  body  of  the 
ninth  thoracic  vertebra.  The  bodies  of  the  thoracic  vertebrae 
project  anteriorly  into  the  cavity  of  the  thorax,  and  greatly 
diminish  its  antero-posterior  diameter  in  the  median  plane ; 
but  the  backward  sweep  of  the  posterior  portions  of  the  ribs 
produces  a  deep  hollow  on  either  side  of  the  vertebral  column, 
for  the  reception  of  the  most  massive  part  of  the  lung. 

The  superior    aperture,  inlet  of  the  thorax^    is    a    narrow 
opening  which  is  bounded  by  the  first  thoracic  vertebra,  the 


Right  vagus  nerve 
Right 
subclavian  artery 

Right 
innominate  vein 


Innominate 
artery- 


Trachea 


CEsophagus 


Left  subclavian  artery 
'  Sulcus  subclavius 


Left  vagus  nerve 

Left 

common 

'carotid 

Left 

innominate 

vein 


Fig.  I. — Cervical  Domes  of  the  Pleural  Sacs,  and  parts  in  relation  to  them, 

first  pair  of  costal  arches,  and  the  manubrium  sterni.  The 
plane  of  this  opening  is  very  obHque ;  it  slopes  from  the  first 
thoracic  vertebra  anteriorly  and  downwards.  Through  the 
inlet  of  the  thorax  the  apices  of  the  lungs  project  upwards 
into  the  root  of  the  neck,  and,  between  them,  the  follow- 
ing structures  pass  through  it : — the  windpipe,  the  gullet,  the 
vagi,  the  phrenic  nerves,  the  left  recurrent  nerve,  the  ganglion- 
ated  sympathetic  trunks,  the  thoracic  duct,  and  the  great 
arteries  and  veins  which  carry  blood  to  and  from  the  head 
and  neck  and  the  upper  limbs. 

The  base  or  inferior  end  of  the  thorax  is  very  wide, 
and  is  sometimes  called  the  outlet.  Anteriorly  it  is  bounded 
by  the  xiphoid  process,  and  posteriorly  by  the  twelfth  thoracic 
vertebra.  Between  these  points  the  lower  margin  of  the 
thorax  presents  a  curved  outline.  Starting  from  the  sternum, 
it  passes  downwards,  laterally,  and  posteriorly,  as  far  as  the 
tip  of  the  eleventh  costal  cartilage ;    thence  it  proceeds  up- 


THORACIC  WALL  3 

wards,  posteriorly,  and  medially  to  the  vertebral  column.  In 
the  first  part  of  its  extent  it  is  formed  by  the  cartilages  of  the 
seventh,  eighth,  ninth,  tenth  and  eleventh  ribs,  and  in  the 
second  part  by  the  lower  border  of  the  twelfth  rib. 

The  lower  margin  of  the  thorax  gives  attachment  to  the 
diaphragm,  a  highly  vaulted  or  dome-shaped  musculo-tendinous 
partition,  which  intervenes  between  the  cavity  of  the  thorax 
above  and  that  of  the  abdomen  below\  It  forms  a  convex 
floor  for  the  thorax,  and  a  concave  roof  for  the  abdomen. 
By  its  upward  projection  it  greatly  diminishes  the  general 
vertical  depth  of  the  thoracic  cavity. 

But  the  diaphragm  does  not  form  an  unbroken  partition. 
It  presents  three  large  openings,  by  means  of  which  structures 
pass  to  and  from  the  thorax,  viz. — (i)  for  the  aorta,  thoracic 
duct,  and  vena  azygos ;  (2)  for  the  oesophagus  and  vagi 
nerves ;  (3)  for  the  inferior  vena  cava.  Besides  these  there 
are  other  smaller  apertures  which  will  be  mentioned  later. 

THORACIC  WALL. 

Two  days  at  least  should  be  devoted  to  the  dissection  of 
the  thoracic  wall. 

In  addition  to  the  osseous  and  cartilaginous  framework, 
the  walls  of  the  chest  are  built  up  partly  by  muscles,  and 
partly  by  membranes,  and  in  connection  with  these  there  are 
numerous  nerves  and  blood-vessels. 

i  External  intercostals. 
Muscles,         .         J  Internal  intercostals. 

I  iransversi  thoracis. 

I^Subcostals. 

I'  Anterior  intercostal  membranes. 
Membranes,  .         .  X  Posterior  intercostal  membranes. 

[Pleural  membrane  (parietal  part). 

r  Intercostal  nerves. 

Nerves  and  Arteries,  J  ^^^^^^^  intercostal  arteries. 

hupenor  mtercostal  arteries. 
1^ Internal  mammary  arteries. 

Dissection. — Portions  of  certain  of  the  muscles  of  the  upper  limb  and 
of  the  abdominal  wall  are  still  attached  to  the  thoracic  wall  on  each 
side.  Antero- posteriorly  the  dissector  will  meet  with  the  pectoralis  major, 
the  pectoralis  minor,  and  the  serratzis  anterior,  whilst  towards  the  lower 
margin  of  the  chest  he  will  recognise  the  recttis  abdomifiis  anteriorly, 
and  the  obliqtius  externus  and  latissimus  dorsi  upon  its  lateral  aspect.  The 
rounded  tendon  of  the  subclavius  may  also  be  seen  taking  origin  from 
the  first  costal  arch.  These  remnants  must  be  removed  so  as  to  lay 
bare  the  costal  arches  and  the  intercostal  muscles.  In  detaching  the 
II — ^1  a 


4  THORAX 

serratus  anterior  and  external  oblique  be  careful  not  to  injure  the  lateral 
cutaneous  nerves  which  make  their  appearance  in  the  intervals  between 
their  digitations.  The  anterior  ctitaneous  nerves  and  perforating  b7'anches  of 
the  internal  mammary  artery  must  also  be  preserved  ;  they  pierce  the 
origin  of  the  pectoralis  major  in  the  intervals  between  the  costal  cartilages, 
close  to  the  margin  of  the  sternum. 

Intercostal  Muscles  and  Membranes. — These  muscles  and 
membranes  occupy  the  eleven  intercostal  spaces  on  each  side. 
In  each  space  there  are  two  strata  of  muscular  fibres — a 
superficial  and  a  deep.  The  superficial  layer  of  muscular 
fibres  is  called  the  external  intercostal  7nuscle^  and  the  deep 
layer  the  internal  intercostal  muscle. 

The  external  intercostal  muscles  are  already  exposed,  and 
very  little  cleaning  is  necessary  to  bring  out  their  connections. 
Note  that  entering  into  their  constitution  there  is  a  large 
admixture  of  tendinous  fibres,  and  that  these,  as  well  as  the 
muscular  fibres,  are  directed  obliquely  downwards  and 
anteriorly  from  the  lower  border  of  the  rib  above  to  the 
upper  border  of  the  rib  below.  They  do  not  extend  farther 
anteriorly,  in  the  various  spaces,  than  the  region  of  union  of 
the  bony  with  the  cartilaginous  parts  of  the  costal  arches.  In 
many  cases,  especially  in  the  upper  spaces,  they  do  not 
reach  so  far.  When  the  muscular  fibres  stop,  the  tendinous 
fibres  are  prolonged  onwards  to  the  sternum  in  the  form 
of  a  membrane,  which  is  called  the  anterior  intercostal  77tem- 
brane.  The  external  intercostal  muscles  of  the  two  lower 
spaces  are  exceptions  to  this  rule.  They  extend  anteriorly  to 
the  extremities  of  the  spaces.  Posteriorly  the  muscles  ex- 
tend as  far  as  the  tubercles  of  the  ribs,  but  this  is  a  point 
which  can  be  satisfactorily  demonstrated  only  after  the  thorax 
has  been  opened. 

Dissection. — To  bring  the  internal  intercostal  muscles  into  view  it  is 
necessary  to  reflect  the  external  intercostal  muscles,  and  also  the  anterior 
intercostal  membranes.  Divide  them  along  the  lower  border  of  each 
space,  and  throw  them  upwards.  In  effecting  this  dissection,  care  must  be 
taken  of  the  intercostal  vessels,  which  lie  between  the  two  muscular  strata, 
and  of  the  lateral  branches  of  the  intercostal  nerves. 

The  internal  intercostal  muscles^  thus  laid  bare,  will  be  seen 
to  be  similar  in  their  constitution  to  the  external  muscles. 
The  fibres,  however,  run  in  the  opposite  direction — viz.,  from 
above,  obliquely  downwards  and  posteriorly.  Superiorly,  each 
is  attached  to  the  inner  surface  of  the  upper  rib,  immediately 
above  the  costal  groove ;  inferiorly,  it  is  attached  upon  the 


THORACIC  WALL  5 

inner  surface  of  the  lower  rib,  close  to  the  upper  margin. 
The  internal  intercostal  muscles  are  prolonged  anteriorly 
to  the  sternum.  Posteriorly  they  extend  to  the  angles 
of  the  ribs.  The  posterior  i?itercosial  7nembra?ies  extend  from 
the  spine  to  posterior  borders  of  the  internal  intercostals 
where  they  become  continuous  with  the  fascial  layer  between 
the  external  and  internal  intercostal  muscles.  They  will 
be  seen  when  the  thorax  is  opened. 

If  the  internal  oblique  muscle  of  the  abdomen  has  not  been  removed, 
the  dissector  should  note  that  the  anterior  fibres  of  the  lowest  two  internal 
intercostal  muscles  become  continuous  with  the  fibres  of  that  muscle. 


Sternum      /     /    /     i 
M.  transversus  thoracis   /    /     / 
Internal  mammary  artery  '     / 
Anterior  intercostal  membrane   \ 

Anterior  cutaneous  nerve        ■ 


//  &^  •■    Vv  Jk^^^    ■■■•  '''  >^^^  Internal  inter- 

C^^^^'ii^^^<\^^^>^       — "Itf!^^^^   costal  muscle 

Trunk  of  thoracic  nerve  -'TI   /' N'         ^^'^^^^IWMSS^^^  Anterior  branch  of  thoracic 
Posterior  branch    {]/     /  >  I       nerye  (intercostal) 

'      /  External  intercostal  muscle 

Anterior  costo-transverse  ligament  ' 

Posterior  intercostal  membrane 

Fig.  2. — Diagram  of  one  of  the  Upper  Intercostal  Xer\-es. 

Intercostal  Nerves. — The  intercostal  nerves  are  altogether 
out  of  sight  in  the  present  stage  of  the  dissection.  They  are 
hidden  by  the  lower  borders  of  the  ribs  which  bound  the 
intercostal  spaces  superiorly.  By  gently  pulling  upon  their 
lateral  cutaneous  branches  they  can  be  drawn  downwards, 
and  they  are  then  seen  to  lie  between  the  two  muscular  strata  as 
far  anteriorly  as  a  point  midway  between  the  vertebral  column 
and  sternum.  There  they  sink  into  the  substance  of  the  in- 
ternal intercostal  muscles,  amidst  the  fibres  of  which  they  may 
be  traced  to  the  anterior  extremities  of  the  bony  parts 
of  the  ribs,  where  they  reach   the   deep    surface  of  internal 


6  THORAX 

intercostal  muscles  and  are  carried  medially,  first  anterior 
to  the  pleura,  and  then  anterior  to  the  transversus  thoracis 
muscle.  Lastly,  they  cross  anterior  to  the  internal  mammary 
artery  and  turn  anteriorly,  at  the  side  of  the  sternum,  as  the 
anterior  cutaneous  nerves  of  the  pectoral  region.  Each  nerve, 
before  it  reaches  the  surface,  pierces — (a)  the  internal  inter- 
costal muscle ;  (^)  the  anterior  intercostal  membrane ;  ic) 
the  origin  of  the  pectoralis  major;  and  {d)  the  deep  fascia 
(Fig.  2). 

This  description  holds  good  for  the  upper  five  inter- 
costal nerves  only.  The  lower  six  nerves  leave  the  anterior 
ends  of  the  intercostal  spaces  and  run  into  the  abdominal 
wall.  As  they  leave  the  thoracic  wall  the  upper  four  of  the 
six  pass  posterior  to  the  upturned  costal  cartilages,  and  all  six 
pass  between  the  interdigitating  slips  of  the  diaphragm  and 
the  transversus  abdominis  muscles. 

The  intercostal  nerves  are  the  anterior  branches  of  the 
upper  eleven  thoracic  nerves.  As  they  traverse  the  thoracic 
wall  they  give  off — {a)  the  lateral  cutaneous  branches,  {f) 
twigs  to  the  intercostal,  subcostal,  and  transversus  thoracis 
muscles.  The  terminal  extremities  of  the  upper  five  become 
the  anterior  cutaneous  nerves  of  the  thorax.  (For  the 
abdominal  distribution  of  the  lower  six  see  Vol.  I.,  p.  394.) 

The  lateral  cutaneous  branches  arise  midway  between  the 
vertebral  column  and  the  sternum.  They  pierce  the  external 
intercostal  muscles,  and  pass  between  the  digitations  of  the 
serratus  anterior. 

The  first  intercostal  nerve  does  not  give  a  lateral  branch, 
and  it  does  not  become  cutaneous  anteriorly.  The  lateral 
cutaneous  branch  of  the  second  intercostal  nerve  is  the  so- 
called  intercosto-brachial  nerve. 

It  is  not  necessary  to  make  a  dissection  of  the  intercostal  nerves  in  more 
than  two  or  three  of  the  spaces. 

Intercostal  Vessels. — The  intercostal  arteries  should  be 
dissected  in  spaces  in  which  the  nerves  have  not  been 
traced,  and  in  which,  therefore,  the  internal  intercostal 
muscles  are  still  entire.  It  is  only  in  a  well-injected  subject 
that  a  satisfactory  view  of  these  vessels  can  be  obtained.  In 
each  intercostal  space  one  artery  is  found  passing  dorso-ven- 
trally ;  and  in  each  of  the  upper  nine  intercostal  spaces,  two 
anterior  intercostal  arteries  run  vent7'o-dor sally. 


THORACIC  WALL  7 

In  the  upper  two  spaces  the  vessels  which  run  dorso- 
ventrally  are  derived  from  the  superior  intercostal  division  of  the 
costo-cervical  branch  of  the  subclavian  artery;  in  the  lower  nine 
spaces  they  spring  directly  from  the  aorta,  and  are  called  the 
aortic  i?itercostal  arteries. 

The  anterior  intercostal  arteries  of  the  upper  six  spaces 
proceed  directly  from  the  internal  mammary,  whilst  those  of 
seventh,  eighth,  and  ninth  spaces  arise  from  the  musculo- 
phrenic artery. 

The  intercostal  vessels  are  distributed  for  the  most  part 
between  the  two  muscular  strata.  From  the  angles  of  the 
ribs  onwards  to  a  point  midway  between  the  vertebral  column 
and  sternum,  the  aortic  intercostal  arteries  lie  under  shelter  of 
the  lower  margins  of  the  ribs  which  bound  the  spaces  superiorly, 
and  at  a  higher  level  than  the  corresponding  nerves.  Then 
each  divides  into  two  branches,  which  pass  ventrally  in 
relation  to  the  upper  and  lower  margins  of  the  intercostal 
space.  They  give  off  small  branches  which  accompany  the 
lateral  cutaneous  nerves.  The  lower  two  aortic  intercostal 
arteries  are  carried  onwards  into  the  abdominal  wall.  The 
branches  of  the  superior  intercostal  artery  are  disposed  in  a 
manner  similar  to  the  aortic  intercostal  vessels. 

The  anterior  intercostal  arteries  are  two  in  number  for  each 
space,  except  the  last  two.  At  their  origins  they  lie  under 
cover  of  the  internal  intercostal  muscles,  and  they  run  later- 
ally in  relation  to  the  upper  and  lower  margins  of  the  ribs 
bounding  the  spaces.  After  a  short  course  they  pierce  the 
internal  intercostal  muscles,  and  end  by  anastomosing  with 
the  aortic  and  superior  intercostal  arteries. 

Dissection. — The  dissector  should  next  proceed  to  remove  the  intercostal 
muscles.  This  dissection  must  be  done  with  great  care,  for  immediately 
subjacent  to  the  internal  intercostals  and  the  ribs  is  the  delicate  pleural 
membrane  which  lines  the  inner  surface  of  the  chest  wall.  The  membrane 
must  not  be  injured  or  detached  from  the  deep  surfaces  of  the  ribs  during 
this  stage  of  the  dissection.  As  the  internal  intercostal  muscles  are  removed, 
the  anterior  perforating  branches  of  the  internal  mammary  and  musculo- 
phrenic arteries,  and  the  anterior  cutaneous  nerves  must  be  preserved. 

When  the  muscles  are  removed  the  internal  mammary  arter}'  with  its 
two  accompanying  veins  will  be  seen  behind  the  costal  cartilages,  about 
half  an  inch  from  the  side  of  the  sternum.  Clean  these  arteries  in  the 
intervals  between  the  cartilages  and  note  the  small  lymph  glands 
which  lie  beside  them.  Each  internal  mammary  artery  ends  by  dividing 
into  superior  epigastric  and  musculo -phrenic  terminal  branches  in  the 
interval  between  the  sixth  and  seventh  rib  cartilages.  Most  likely  this 
space  will  be  so  narrow  that  a  view  of  the  bifurcation  cannot  be  obtained. 
If  this  is  the  case,  pare  away  the  edges  of  the  cartilages  over  the  artery,  or, 
11—16 


8 


THORAX 


if  necessary,  remove  the  medial  part  of  the  sixth  cartilage  completely.  The 
muscle  posterior  to  the  internal  mammary  artery  is  the  transversus  thoracis 
(O.T,  triangularis  sterni).  Endeavour  to  define  its  slips  in  the  intervals 
between  the  costal  cartilages. 

The  dissector  should  note,  as  an  important  practical  point,  that  towards 
the  lower  margin  of  the  thorax  the  pleural  sac  is  not  prolonged  downwards 
to  the  lowest  limit  of  the  recess  between  the  diaphragm  and  the  costal 
arches.     Indeed,  in  the  axillary  line,  it  will  be  found  to  fall  considerably 


Sterno-hyoid  -~:4^v 
Sterno-thyreoid — |'A  ^/||/ 

Transversus  thoracis 


Intercostal  nerve 
and  artery 
\ 


Internal  mammary 
artery 

Sternal  glands 


Transversus 
oracis 

Musculo- 
phrenic artery 


Musculo-  \>, 

phrenic 

artery 

Fig.  3.- — Dissection  of  the  posterior  surface  of  the  Anterior  Wall  of  the  Thorax. 


short  of  this.  Consequently  the  dissector  will  come  down  directly  upon 
the  diaphragm,  when  the  internal  intercostal  muscles  are  removed  from 
this  portion  of  the  chest  wall.  The  fibres  of  the  diaphragm  correspond 
somewhat  in  their  direction  with  those  of  the  internal  intercostal  muscles, 
and  it  is  no  uncommon  occurrence  for  the  student  to  remove  them,  and 
thus  expose  the  peritoneum,  under  the  impression  that  he  has  simply  laid 
bare  the  pleura.  When  the  dissection  is  properly  executed  a  strong  fascia 
will  be  seen.  It  passes  from  the  surface  of  the  diaphragm  to  the  surface 
of  the  costal  pleura  and  holds  the  latter  in  position.  Preserve  this  mem- 
brane for  further  examination. 


THORACIC  WALL  9 

Arteria  Mammaria  Interna. — This  vessel  arises,  in  the  root 
of  the  neck,  from  the  first  part  of  the  subclavian.  It  enters 
the  thorax  by  passing  downwards,  posterior  to  the  sternal  end 
of  the  clavicle  and  the  cartilage  of  the  first  rib,  and  it  descends 
to  the  interval  between  the  sixth  and  seventh  costal  cartilages, 
where  it  ends  by  dividing  into  the  superior  epigastric  and  the 
musculo-phrenic  branches. 

Placed  anterior  to  the  internal  mammary  artery  are  the 
upper  six  costal  cartilages,  with  the  intervening  internal  inter- 
costal muscles  and  anterior  intercostal  membranes.  The  inter- 
costal nerves  cross  anterior  to  it  before  they  turn  forwards  to 
gain  the  surface.  Posterior  to  the  upper  part  of  the  artery  is 
the  pleura ;  and  the  transversus  thoracis  intervenes  between 
the  lower  part  of  the  artery  and  the  pleural  sac. 

In  addition  to  its  two  terminal  branches,  a  large  number 
of  small  collateral  twigs  proceed  from  the  internal  mammary — 


1.  The  anterior  intercostal,  .^  -     .1     .v         •  •  ^ 
rr.,           r      ,-                  '     >  to  the  thoracic  parietes. 

2.  The  perforating,       .         .  J  ^ 

3.  The  pericardio-phrenic, 

4.  Mediastinal  and  thymic, 

5.  Superior  epigastric, 

6.  Musculo-phrenic, 


\  to  parts  in  the  interior  of  the  thorax. 
\  the  terminal  branches. 


The  anterior  intercostal  arteries  are  supplied  to  the  upper  six 
intercostal  intervals,  and  have  been  dissected  already  (p.  6). 
Two  are  given  to  each  space :  frequently  these  arise  by  a 
common  trunk. 

The  perforating  arteries  accompany  the  anterior  cutaneous 
nerves,  and  reach  the  surface  by  piercing  the  internal  inter- 
costal muscles,  the  anterior  intercostal  membranes,  and  the 
pectoralis  major  muscle.  One,  or  perhaps  two,  are  given 
off  in  each  intercostal  space.  In  the  female  those  of  the 
second,  third,  and  fourth  spaces  attain  a  special  importance, 
inasmuch  as  they  constitute  the  principal  arteries  of  supply  to 
the  mammary  gland. 

The  superior  epigastnc  artery  passes  between  the  sternal  and 
costal  origins  of  the  diaphragm  and  enters  the  sheath  of  the 
rectus  muscle  of  the  abdominal  wall. 

The  musculo-phrenic  artery  turns  laterally  and  downwards, 
along  the  costal  origin  of  the  diaphragm  and  behind  the  rib- 
cartilages.  Opposite  the  eighth  costal  cartilage  it  pierces  the 
diaphragm  and  terminates  on  its  abdominal  surface.  It  gives 
off  the  anterior  intercostal  arteries  to  the  seventh,  eighth,  and 
ninth  intercostal  spaces  (p.  7). 


lo  THORAX 

Musculus  Transversus  Thoracis  (O.T.  Triangularis  Sterni). 

- — This  is  a  thin  muscular  layer  placed  on  the  deep  surface  of 
the  sternum  and  costal  cartilages.  It  is  continuous  below 
with  the  transversus  abdominis,  and  arises  from  the  posterior 
surface  of  the  xiphoid  process,  the  lower  part  of  the  body  of 
the  sternum,  and  from  the  medial  ends  of  the  fifth,  sixth,  and 
seventh  costal  cartilages.  Its  fibres  radiate  in  an  upward  and 
lateral  direction,  in  the  form  of  five  slips,  which  are  inserted 
into  the  deep  surfaces  and  lower  borders  of  the  second,  third, 
fourth,  fifth,  and  sixth  costal  cartilages,  close  to  their  junction 
with  the  ribs  (Fig.  3). 

In  many  cases  the  muscle  is  feebly  developed,  and  does  not  show 
such  wide  connections.  Upon  its  anterior  aspect  are  placed  the  internal 
mammary  artery  and  some  of  the  intercostal  nerves. 

It  is  only  a  partial  view  of  the  muscle  which  is  obtained  in  the  present 
dissection,  but  it  is  not  advisable  to  remove  the  costal  cartilages  to  expose 
it  further,  as  this  would  materially  interfere  with  the  subsequent  display 
of  other  more  important  structures  in  their  proper  relations. 


THORACIC    CAVITY. 

Before  the  dissection  of  the  interior  of  the  thorax  is  com- 
menced it  is  necessary  that  the-  dissectors  should  have  some 
general  knowledge  of  the  cavity  and  its  contents.  The  shape 
and  the  boundaries  have  been  studied  already  (p.  i),  and  it 
must  now  be  understood  that  the  cavity  is  divided  into  two 
lateral  parts  by  a  median  septum  called  the  Jiiediastinmn^ 
which  extends  from  the  sternum  anteriorly  to  the  vertebral 
column  posteriorly,  and  from  the  upper  aperture  of  the  thorax 
above  to  the  diaphragm  below. 

The  mediastinum  is  formed  by  the  heart,  enveloped  in  a 
fibro-serous  sac  called  the  pericardium ;  the  great  vessels 
passing  to  and  from  the  heart,  i.e.  the  pulmonary  artery  and 
veins,  the  aorta,  and  the  vena  cava  superior ;  the  oesophagus ; 
the  trachea  and  the  commencements  of  the  bronchi ;  the 
thoracic  duct ;  the  azygos,  hemiazygos  and  accessory  hemi- 
azygos veins ;  the  vagi  and  phrenic  nerves ;  numerous  lymph 
glands  ;  and  the  areolar  tissue  in  which  these  structures  are 
embedded  and  by  which  they  are  bound  together.  For  con- 
venience of  description  the  mediastinum  is  divided  into  a 
superior  and  an  inferior  portion^  by  an  imaginary  plane 
which  passes  from  the  lower  border  of  the  manubrium  sterni 
anteriorly,  to  the  lower  border  of  the  fourth  thoracic  vertebra 


THORACIC  CAVITY 


II 


posteriorly ;  and  the  inferior  mediastinum  is  subdivided  into 
anterior,  middle,  and  posterior  portions.  The  anterior 
mediasti7ium  is  the  part  anterior  to  the  pericardium,  the 
posterior  viediastijium  the  part  posterior  to  the  pericardium, 
whilst  the  pericardium  and  the  heart  with  the  great  vessels 
and  the  phrenic  nerves  with  their  accompanying  vessels  form 
the  middle  inediastifium.  It  is  customary,  however,  to  speak  of 
the  mediastinum  as  if  it  were  a  space,  and  to  say  that  the  various 
viscera,  vessels,  etc.,  lie  in  the  mediastina  (Fig.  19,  p.  44). 
The  lateral  portions  of  the  thoracic  cavity  are  known  as 


Costal  part  of  parietal  pleura 

Pleural  cavity 
Visceral  pleura 


Costal  part  of  parietal  pleura 
Pleural  cavitj' 
Visceral  pleura 


Fig.  4.  — Diagrammatic  representation  of  a  cross  section  through 
the  Thorax. 

the  pleural  spaces ;  each  contains  the  corresponding  lung 
surrounded  by  an  invaginated  serous  membrane  called  the 
pleural  sac.  There  are  therefore  two  pleural  sacs,  and  each  is 
so  disposed  that  it  not  only  lines  the  chamber  in  which  the  lung 
lies,  but  is  also  reflected  over  the  surface  of  the  lung,  so  as  to 
give  it  an  external  covering  which  is  intimately  connected  with 
the  pulmonary  substance.  Consequently,  the  wall  of  each 
pleural  sac  is  separable  into  two  portions,  an  investing  or 
visceral  part  which  covers  the  surface  of  the  lung,  and  a  lining  or 
parietal  part  which  clothes  the  inner  surfaces  of  the  boundary 
of  each  lateral  part  of  the  thoracic  cavity.  It  must  be  clearly 
understood,  however,  that  the  two  terms  are  merely  applied 
to  indicate  different  portions  of  a  continuous  membrane. 


12  THORAX 

Each  lung  lies  free  in  the  pleural  space  except  along  its 
medial  surface,  where  it  is  attached  to  the  heart  by  the 
pulmonary  vessels,  to  the  corresponding  bronchial  tube,  and 
by  a  fold  of  pleura  to  the  side  of  the  pericardium. 

The  dissection  which  has  already  been  made  shows  the 
pleura  lining  the  deep  surfaces  of  the  costal  arches  and  the 
internal  intercostal  muscles.  This  part  is  called  the  costal 
pleura,  and  it  is  part  of  the  parietal  pleura,  but  before  it  can 
be  more  fully  investigated  and  before  the  remaining  parts  of 
the  pleurae  and  the  lungs  can  be  examined,  further  dissection 
is  necessary. 

Dissection. — The  pleural  membrane  previously  exposed  by  the  removal 
of  the  contents  of  the  intercostal  spaces  must  now  be  carefully  separated 
from  the  inner  surfaces  of  the  ribs  by  the  gentle  pressure  of  the  fingers. 
The  separation  should  be  carried  anteriorly  to  the  junction  of  the  ribs 
with  their  cartilages  and  posteriorly  as  far  as  possible.  When  this  has 
been  done  the  ribs,  from  the  second  to  the  sixth  inclusive,  must  be  divided, 
with  bone  forceps,  at  their  junctions  with  their  cartilages,  and  at  the  same 
time  any  fibres  of  the  transversus  thoracis  which  may  be  attached  to  them 
must  be  cut.  The  first  and  the  seventh  and  those  below  the  seventh  vnist 
not  be  interfered  with.  Afterwards  the  ribs  must  be  divided  as  far 
dorsally  as  possible  and  the  separated  portions  removed.  After  the  separ- 
ated parts  of  the  ribs  are  detached,  remove  any  sharp  spicules  of  bone 
from  the  cut  ends  of  the  remaining  portions. 

The  outer  surface  of  the  costal  part  of  the  parietal  pleura  will  be  exposed 
in  the  area  from  which  the  ribs  have  been  removed,  and  the  dissector 
should  notice  that  it  has  the  appearance  of  a  fibrous  membrane  with  a 
rough  surface,  the  roughness  being  due  to  fragments  of  the  connective  tissue 
(endothoracic  fascia)  which  connect  it  with  the  adjacent  parts. 

After  he  has  examined  the  outer  surface  of  the  pleura,  the  dissector 
should  divide  it  by  a  vertical  incision  about  midway  between  the  anterior 
and  posterior  borders  of  the  area  exposed.  At  each  end  of  the  vertical 
incision  a  transverse  incision  must  be  made.  One  of  the  two  flaps  so 
formed  must  be  thrown  anteriorly,  and  the  other  posteriorly.  The  pleural 
sac  is  now  opened  and  the  lateral  surface  of  the  lung,  covered  with  the 
visceral  portion  of  the  pleura,  is  exposed. 

The  cavity  of  the  sac  and  its  relations  to  the  mediastinal  septum,  the 
diaphragm,  and  the  root  of  the  neck  can  be  explored  with  the  fingers ;  and 
the  borders,  surfaces,  and  the  root  of  the  lung  can  be  examined. 

The  Pleural  Sacs  are  two  in  number,  a  right  and  a  left. 
They  are  serous  sacs,  and  are  therefore  closed.  After 
opening  into  the  interior,  the  dissector  should  notice  the 
difference  between  the  rough  outer  surface  of  the  wall  of  the 
sac  and  its  smooth  and  ghstening  inner  surface,  and  in  order 
that  he  may  thoroughly  understand  the  relationship  of  the 
wall  of  the  sac  to  the  lung,  the  mediastinum  and  the  wall  of 
the  thoracic  cavity,  he  should  follow  the  wall  of  the  sac,  with 
his  fingers,  at  three  different  levels — (i)  at  the  level  of  the 


THORACIC  CAVITY  13 

manubrium  sterni ;  (2)  at  the  level  of  the  third  intercostal 
space ;  and  (3)  at  the  level  of  the  fifth  costal  cartilage.  He 
must  trace  the  wall  of  the  sac  in  the  vertical  plane  also. 

Commencing  at  the  level  of  the  third  intercostal  space,  he 
should  place  his  fingers  on  the  surface  of  the  lung  and  follow 
it  anteriorly  and  medially  until,  behind  the  sternum,  he  reaches 
the  sharp  anterior  border,  which  should  be  pulled  laterally  ; 
then,  turning  from  the  lung  to  the  parietal  pleura,  he  should 
place  his  fingers  on  the  inner  surface  of  the  anterior  flap  and 
follow  it  medially.  He  will  find,  at  a  certain  point  posterior 
to  the  sternum,  and  to  the  left  of  the  median  plane,  that  his 
fingers  cease  to  pass  towards  the  opposite  side  but  are 
carried  posteriorly,  along  the  lateral  boundary  of  the  medi- 
astinum, until  they  come  to  the  big  blood  vessels  and  the  air 
tube  of  the  lung  which  collectively  form  its  root.  Along  the 
front  of  the  vessels  his  fingers  will  now  pass  laterally,  following 
the  reflection  of  the  pleura  on  the  front  of  the  vessels,  to  the 
medial  surface  of  the  lung,  and  then  anteriorly  to  its  anterior 
border.  Round  the  anterior  border  they  will  arrive  at  the 
lateral  surface  of  the  lung ;  along  this  they  will  pass  to  the 
posterior  border  and  thence  anteriorly  along  the  posterior  part 
of  the  medial  surface  to  the  posterior  surface  of  the  root, 
where  they  will  feel,  distinctly,  the  hard  outline  of  the 
bronchus.  Following  the  posterior  surface  of  the  root  medially, 
they  will  reach  the  posterior  part  of  the  lateral  boundary  of 
the  mediastinum,  along  which  they  will  pass  posteriorly  to  the 
vertebral  column,  and  thence  laterally  along  the  posterior  parts 
of  the  ribs,  and  finally  anteriorly  along  the  inner  surface  of  the 
posterior  flap  to  its  anterior  margin. 

If  the  dissector  has  followed  the  above  instructions  he 
cannot  fail  to  have  recognised  that  the  pleural  sac  is  in- 
vaginated  by  the  lung,  which  in  its  growth  laterally  from 
the  mediastinal  septurh  has  invaginated  and  expanded  a  part 
of  the  medial  wall  of  the  sac.  The  dissector  should  now 
examine  a  transverse  section  of  a  hardened  thorax,  or  if 
that  is  not  available,  the  diagram  on  p.  11.  The  study  of 
either  will  convince  him  that  the  lung  carrying  the  in- 
vaginated part  of  the  wall  of  the  pleural  sac  on  its  surface 
has  expanded  until  it  has  practically  obliterated  the  cavity  of 
the  sac,  and  he  will  find  that  the  invaginated  pleura  on  the 
surface  of  the  lung,  which  is  called  the  visceral  pleura^  is 
everywhere    in    close    apposition    with    the    non -invaginated 


14  THORAX 

portion  which  is  termed  the  parietal  pleura ;  all  that  inter- 
venes between  the  two  portions  being  a  thin  stratum  of  fluid, 
sufficient  to  lubricate  the  surfaces  and  prevent  friction  during 
the  movements  of  the  lung  and  the  chest  wall. 

After  he  has  grasped  the  facts  noted  above  the  dissector 
should  follow  the  inner  surface  of  the  pleura  in  the  transverse 
plane  at  the  level  of  the  fifth  costal  cartilage,  that  is,  below 
the  level  of  the  root  of  the  lung.  At  that  level  he  will  find 
that  the  parietal  pleura  covering  the  lateral  surface  of  the 
mediastinal  septum  is  connected  with  the  visceral  pleura  on 
the  medial  surface  of  the  lung  by  a  thin  fold,  the  pulmonary 
ligament  (O.T.  ligamentum  latum  pulmonis).  This  consists  of 
an  anterior  and  a  posterior  layer,  which  correspond,  respectively, 
with  the  layers  on  the  front  and  the  back  of  the  root  of  the 
lung,  but  are  in  contact  with  each  other  at  the  level  of 
the  fifth  rib,  on  account  of  the  absence  of  the  great  blood 
vessels  and  air  tube  of  the  lung.  The  pulmonary  ligament 
extends  laterally  from  the  mediastinum  to  the  medial  surface 
of  the  lung,  and  from  the  root  of  the  lung  above,  to  within 
a  short  distance  from  the  diaphragm  below.  Its  medial, 
lateral,  and  upper  borders  are  attached  respectively  to  the 
mediastinal  septum,  the  lung,  and  the  lower  border  of  the 
lung  root,  and  are  continuous  with  the  pleura  covering  each, 
but  its  lower  border  is  free.  When  he  has  satisfied  himself 
regarding  the  nature  and  the  attachments  of  the  pulmionary 
ligament,  the  dissector  should  trace  the  pleura  in  the  hori- 
zontal plane  at  the  level  of  the  manubrium  sterni,  that  is, 
above  the  level  of  the  root  of  the  lung.  There  he  will  find 
that  the  medial  wall  of  the  sac  is  not  reflected  on  to  the  lung, 
but  that  it  passes  posteriorly  along  the  lateral  surface  of  the 
mediastinal  septum  from  the  sternum  anteriorly  to  the  vertebral 
column  posteriorly,  and  thence  laterally  and  anteriorly  to  the 
sternum  in  an  unbroken  circle.  In  the  same  way  he  will 
be  able  to  trace  the  visceral  pleura  in  a  similar  but  smaller 
unbroken  circle  around  the  upper  part  of  the  lung. 

Having  traced  the  pleura  in  three  horizontal  planes  the 
dissector  must  next  trace  it  in  the  vertical  plane,  first  around 
the  lung,  and  then  around  the  wall  of  the  thorax.  Commencing 
with  the  lung,  the  fingers  should  be  passed  along  the  anterior 
border  to  the  apex,  thence,  down  the  thick  posterior  border,  to 
the  base,  and  anteriorly,  across  the  concave  base,  to  the  anterior 
border.      By  doing  this  he  will  again  demonstrate  to  himself 


THORACIC  CAVITY 


15 


the  fact  that  the  lung  is  ensheathed  in  visceral  pleura.  Next, 
placing  his  fingers  on  the  inner  surface  of  the  parietal  pleura 
behind  the  costal  cartilages,  he  should  carry  them  upwards 
towards  the  head,  and  he  will  find  that  they  pass  upwards  into 
the  root  of  the  neck  for  a  distance  of  from  one  to  two  inches 
above  the  level  of  the  anterior  part  of  the  first  rib,  but,  on 
account  of  the  oblique  position  of  the  rib,  only  to  the  level  of 
its  neck  posteriorly.      The  apex  of  the  sac,  therefore,  lies  in 


~  Sternum 


Discus  articularis 

Clavicle 

Internal  mammary 


First  rib   - 


Phrenic  nerve 

Right  subclavian 

vein 

Right  vertebral  vein 

Ansa  subclavia 
Right  subclavian 
artery- 
Eighth  cervical 
nerve 
Anterior  branch  of 
first  thoracic  nerve 

Anterior  branch  of 

second  intercostal 

nerve 

Lateral  branch  of 

second  intercostal 

nerve 

Cut  lower  edge  of 

pleura 

Third  rib 


artery 

Innominate  artery 
Right  innominate 
vein 

Trachea 

Right  vagus 

Right  recurrent 

nerve 

First  thoracic  sj'^m- 

pathetic  ganglion 

Superior  intercostal 

artery 

Third  thoracic 

vertebra 

Second  intercostal 
nerve 


Fig.  5. — Structures  in  relation  with  the  apex  of  the  pleural  sac, 
seen  from  below. 


the  root  of  the  neck,  and  by  carefully  palpating  its  inner 
surface  the  dissector  will  be  able  to  distinguish  the  subclavian 
artery  which  passes  across  its  anterior  surface  below  the  highest 
point,  and,  possibly,  he  may  be  able  to  locate  the  internal 
mammary  and  costo-cervical  arteries  (O.T.  superior  inter- 
costal). The  first  descends  from  the  subclavian  trunk 
anterior  to  the  apex  of  the  sac,  and  the  second  passes  first 
upwards  to  the  apex  and  then  posteriorly  above  it.  After  the 
dissector  has  examined    the    position  and   relations   of   the 


1 6  THORAX 

apex  of  the  sac  he  should  follow  its  posterior  wall  downwards, 
just  lateral  to  the  line  of  the  vertebral  column,  and,  if  he  is 
dealing  with  a  subject  in  good  condition,  he  will  find  that  he 
can  pass  his  fingers  downwards  to  the  lower  border  of  the 
twelfth  rib,  where  they  will  be  carried  anteriorly  on  to  the 
diaphragm  and  over  its  surface  to  the  anterior  wall  of  the 
thorax.  If  the  dissector  carries  out  the  examination  of  the 
pleural  sac  in  a  thorough  manner,  and  if  he  has  appreciated 
the  significance  of  the  arrangements  found  at  different  levels, 
he  will  have  repeatedly  convinced  himself  that  the  lung, 
carrying  the  blood  vessels  and  air  tube  with  it,  has  invaginated 
a  portion  of  the  lower  part  of  the  medial  wall  of  the  pleural 
sac,  and  has  then  expanded  anteriorly,  posteriorly,  upwards  and, 
to  a  certain  extent,  downwards  beyond  the  margins  of  the 
aperture  of  invagination,  whose  position  is  indicated  by  the 
root  of  the  lung  and  the  line  of  attachment  of  the  pulmonary 
ligament.  The  portion  of  the  wall  of  the  pleura  which  is 
invaginated  by  the  lung  is  represented  by  (i)  the  visceral 
pleura,  (2)  the  layers  covering  the  root  of  the  lung,  and  (3) 
the  pulmonary  ligament. 

Before  each  lung  is  removed  the  dissectors  should  note 
that  its  anterior  margin  does  not  extend  so  far  anteriorly,  and 
the  inferior  margin  does  not  extend  so  far  downwards,  as  the 
corresponding  part  of  the  pleura.  The  portions  of  the 
pleura  unoccupied  by  the  lung  are  called  the  pleural  sinuses. 
The  sinus  along  the  anterior  margin  of  the  pleura  is  the 
costo-mediastinal  sinus^  and  that  along  the  lower  margin,  the 
phrenico-costal  sinus.  The  walls  of  the  sinuses  are  separated 
by  a  capillary  space  filled  with  pleural  fluid,  and  the  margins 
of  the  lungs  enter  into  the  sinuses  and  recede  from  them 
during  inspiration  and  expiration,  respectively. 

In  the  event  of  the  lungs  not  having  been  hardened  in  situ  by  formalin 
injection  the  dissectors  may,  with  the  consent  of  the  dissectors  of  the  head 
and  neck,  introduce  the  nozzle  of  the  bellows  into  the  cervical  part  of 
the  trachea  and  inflate  the  lungs  with  air.  A  truer  conception  of  these 
organs  will  thus  be  obtained,  and  a  demonstration  will  be  afforded  of  their 
high  elasticity,  and  of  their  connection  with  the  wind-pipe. 

After  the  dissector  has  completed  the  general  examination 
of  the  walls  of  the  pleural  sac,  he  should  pull  the  anterior 
margin  of  the  lung  laterally  to  expose  its  medial  surface, 
the  front  of  the  root  and  the  front  of  the  pulmonary  ligament ; 
then  he  should  divide  the  root  and  the  pulmonary  ligament, 
from  above  downwards,  close  to  the  medial  surface   of  the 


THORACIC  CAVITY 


17 


lung.  The  lung,  thus  set  free,  is  to  be  removed  from  the 
thorax,  wrapped  in  a  cloth  damped  with  preservative  solution, 
and  placed  aside  for  future  study. 

When  the  lung  has  been  removed  the  margins  of  the 
pleural  sac  must  be  examined,  and  their  positions  relative  to 
the  chest  wall  noted.  This  cannot  be  done  to  the  best 
advantage  until  both  lungs  have  been  removed.  When  this 
has  been  done  the  dis- 
sector should  introduce 
one  hand  into  each 
pleura,  and  placing  an 
index  finger  in  each 
apex,  he  should  note 
that  the  apex  is  situated 
about  one  inch  above 
the  junction  of  the 
lateral  two-thirds  with 
the  medial  third  of  the 
clavicle,  a  fact  which 
he  can  demonstrate 
with  the  aid  of  his 
partner  on  the  opposite 
side,  who  should  hold 
two  macerated  clavicles 
in  their  proper  posi- 
tions. The  apices  of 
opposite  sides,  there- 
fore, are  some  distance 
apart,  and  are  separ- 
ated from  each  other 
by  the  structures  occu- 
pying the  median  part 
of  the  neck ;  i.e.  the 
air  tube,  the  gullet,  and  the  great  arteries  passing  upwards  to  the 
head.  As  the  anterior  margins  of  the  pleurae  are  traced  down- 
wards from  the  apices  they  will  be  found  to  converge,  passing 
behind  the  sterno-clavicular  joints  and  coming  into  apposition 
at  the  lower  border  of  the  manubrium  sterni,  immediately  to 
the  left  of  the  median  plane.  Traced  further  downwards  the 
anterior  margins  remain  in  apposition,  the  right  frequently  over- 
lapping the  left  and  both  inclining  slightly  to  the  left,  to  the 
level  of  the  fourth  costal  cartilages.     From  the  fourth  cartilage 

VOL.  II — 2 


P'iG.  6. — Diagram  to  show  the  relation  of  the 
lungs  and  the  pleural  sacs  to  the  anterior 
thoracic  wall.  The  lungs  are  depicted  in 
red,  and  the  pleural  sacs  in  blue. 


1 8  THORAX 

the  anterior  margin  of  the  right  sac  continues  to  descend,  still 
with  a  slight  inclination  to  the  left,  till  it  reaches  the  xiphoid 
process,  where  it  becomes  continuous  with  the  inferior  margin. 
This  turns  laterally,  passing  behind  the  xiphoid  process  and 
the  cartilage  of  the  seventh  rib ;  it  then  crosses  the  junction 


Cervical  dome  of  pleura 

Left  subclavian  artery 
Left  common  carotid  artery 


Internal  mam-    '''^^ 
mary  artery 


Anterior  margin 

of  right 

pleural  sac 


Intercostal  nerve 


Pericardium 


Transversus  (J 
thoracis 


Diaphragm 


Left  innominate  vein 


Fig.  7. — Diagram  to  show  the  parts  which  He  anterior  to  the  pericardium 
and  heart.  The  outline  of  the  heart  is  indicated  in  red  by  a  dotted  line, 
and  the  anterior  margins  of  the  pleural  sacs  are  represented  by  blue  lines. 

of  the  bone  and  cartilage  of  the  eighth  rib  and  reaches 
the  level  of  the  tenth  rib  in  the  mid-axillary  line ;  turning 
posteriorly,  it  crosses  the  eleventh  and  twelfth  ribs,  and  just 
below  the  middle  of  the  latter  it  becomes  continuous  with  the 
posterior  margin,  which  ascends  along  the  line  of  the  angle  of 
the  ribs  to  the  apex.  On  the  left  side,  at  the  level  of  the 
fourth  costal  cartilages,  the  anterior  margin  of  the  left  pleura 
turns   away  from  the  median  plane,  for  a  variable  distance, 


THORACIC  CAVITY 


19 


passing  behind  the  fifth  costal  cartilage  at  the  margin  of  the 
sternum,  or  even  an  inch  more  laterally;  it  then  descends 
to  the  lower  border  of  the  sixth  cartilage,  where  it  becomes 


Ollsophagus 
Left  subclavian  artery 
Left  common  carotid  artery  ^ 
Left  superior  intercostal  vein  \  \    \ 
Left  innominate  vein 


Cut  edge  of 
parietal  pleura 


Pericardium 


Cut  edge  of 
parietal  pleura 


Aortic  arch 

Pulmonarj- 
arterj' 

Bronchus 


Lower  pulmon- 
ary vein 


Oesophagus 


Diaphragmatic 
pleura 


Fig.  8. — Left  Pleural  Sac,  of  a  subject  hardened  by  formalin  injection, 
opened  into  by  the  removal  of  the  costal  pleura.  The  left  lung  also 
has  been  removed  so  as  to  display  the  mediastinal  pleura.  The  line 
along  which  the  pleura  is  reflected  from  the  diaphragm  on  to  the  thoracic 
wall  is  exhibited. 

continuous  with  the  lower  margin  of  the  pleura,  which  passes 
laterally  and  posteriorly  along  the  lower  border  of  the  sixth 
cartilage,  across  the  medial  end  of  the  sixth  space,  and  across 
the  seventh  cartilage  to  the  junction  of  the  cartilage  and 
II — la 


20 


THORAX 


bone  of  the  eighth  rib.      The  remainder  of  its  course  and  the 
posUion  of  Its  posterior  margin  are  the  same  as  on  the  right 

Cervical  dome  of  pleura 


Cut  edge  of 
parietal  pleura' 

Trachea 


Vena  azygos 

Eparterial 

branch  of 

bronchus 

Pulmonary 

artery 

Bronchus 
(hyparterial  part) 

Pulmonary  veins 


Inferior  vena 

cava 

Cut  edge  of 

parietal  pleura 


Right  innominate  vein 


Left  innominate 
vein 

Superior  vena 
cava 

Aorta 
within  the 
pericardium 


Cut  edge  of 
parietal  pleura 


Phrenic  nerve 
Pericardium 


Diaphragmatic 
pleura 


Stn^^i  ^i      K '"°''^^  °^  '^"  '°''^^  P^^*  °^  *^  P^^i^tal  pleura.     Th^ 

Not  tSinrnf  ?     .'"  '"^^^'^  '°  ""''^'^y  '^'  ^^^^^  mediastinal  pleura. 
iNote  the  line  of  diaphragmatic  reflection  of  the  pleura. 

The  Student  should  mark  out  the  margins  of  the  pleural 
sacs  on  the  livmg  body,  using  himself  and  his  friends  for  the 
purpose,  until  he  can  indicate  them  correctly,  judging  from 
the  contour  of  the  body  alone  and  without  feeling  for  the 
Skeletal  pomts. 


THORACIC  CAVITY  21 

After  the  dissector  has  made  himself  thoroughly  conversant 


Thoracic  sym- 
pathetic trunk 
Intercostal  ^ 
vessels  and  nerve  ~T 

/f 
Vena  azj^gos  ~~j^  ^ 

Pulmonarjf  \i ^ 

artery 
Eparterial 
branch  of     nAtM/f 

right 
bronchus      O'^ 
Hyparterial    ;ijjy 
part  of  ~^    * ' 
bronchus 


Scalenus  anterior 
Brachial  nerves 

Right  subclavian  artery 
Right  subclavian  vein 

Right  innominate  vein 
Internal  mammary  artery 
rachea 

Right  vagus  nerve 

Left  innominate  vein 


Ascending  aorta 

Superior 
\  ena  cava 


Internal  mam- 
mary artery 
Phrenic  nerve 
and  accom- 
panying artery 


Pericardium 
and  heart 


Diaphragm 


Fig.  10. — The  Right  Pleural  Chamber  opened  up  by  the  removal  of  its  lateral 
wall.      The  lung  has  been  taken  away  so  as  to  expose  the  mediastinal 
wall  of  the  pleural  chamber.      Several  of  the  structures  in  the  medias- 
tinal septum  are  seen  shining  through  the  mediastinal  pleura. 
II— 2  & 


2  2  THORAX 

with  the  limits  of  the  pleural  sacs,  he  should  examine  the  cut 
section  of  the  root  of  the  lung,  and  should  endeavour  to 
recognise,  through  the  mediastinal  part  of  the  parietal  pleura, 
the  positions  of  the  main  constituent  parts  of  the  mediastinum. 
As  these  vary  on  the  opposite  sides,  each  side  must  be  con- 
sidered separately,  and  each  dissector  must  make  himself  well 
acquainted  with  the  conditions  on  both  sides. 

On  the  right  side,  in  the  posterior  part  of  the  face  of  the  section 
of  the  lung  root,  at  least  two  parts  of  the  bronchial  tube  will 
be  seen  ;  an  upper,  which  is  the  so-called  eparterial  bronchus, 
and  a  lower,  the  main  stem  of  the  right  bronchus.  Anterior 
to  and  between  the  two  bronchi  is  the  pulmonary  artery,  and 
more  anteriorly,  and  at  a  slightly  lower  level,  the  upper  pul- 
monary vein.  The  lower  pulmonary  vein  lies  in  the  lowest 
part  of  the  root,  below  and  slightly  posterior  to  the  main 
bronchus.  If  the  specimen  is  well  injected,  branches  of  the 
right  bronchial  artery  may  be  distinguished  on  the  posterior 
faces  of  the  air  tubes ;  and  anterior  to  and  between  the  great 
blood  vessels,  and  between  them  and  the  bronchi,  are  a 
number  of  bronchial  glands,  which  are  easily  distinguished 
by  the  black  pigment  deposited  within  them. 

In  the  posterior  part  of  the  root  of  the  lung,  on  the  left  side, 
the  dissectors  will  see  the  cut  section  of  the  left  bronchus, 
and,  in  many  cases,  a  section  of  its  first  ventral  branch  also. 
The  left  pulmonary  artery  is  above  the  bronchus,  and  its 
anterior  wall  is  on  a  slightly  anterior  plane.  The  upper  left 
pulmonary  vein  is  anterior  to  the  bronchus,  and  the  lower 
left  pulmonary  vein  is  below  the  bronchus.  In  a  well  in- 
jected specimen  the  two  left  bronchial  arteries  may  be  seen 
on  the  posterior  wall  of  the  bronchus,  and  a  number  of 
bronchial  glands  will  be  found  between  and  around  the  large 
blood  vessels  and  the  bronchus. 

Turning  next  to  the  mediastinal  pleura  oit  the  right  side, 
the  dissectors  will  note,  anterior  to  and  below  the  root  of  the 
lung,  a  large  bulging,  due  to  the  heart  and  pericardium,  which 
lie  in  the  middle  mediastinal  area.  Continuous  with  the 
upper  and  lower  ends  of  the  posterior  part  of  this  bulging 
they  will  see  two  longitudinal  elevations.  The  upper,  from 
the  level  of  the  third  costal  cartilage  to  the  lower  margin 
of  the  first  rib,  is  due  to  the  superior  vena  cava  and  above 
that  level,  to  the  right  innominate  vein.  The  lower  elevation 
is  very  short,  and  is  caused  by  the  upper  part  of  the  inferior 


THORACIC  CAVITY  23 

vena  cava.  A  secondary  ridge,  formed  by  the  phrenic  nerve 
and  the  accompanying  blood  vessels,  descends  along  the 
elevation  caused  by  the  superior  vena  cava,  crosses  anterior 
to  the  root  of  the  lung,  runs  down  along  the  posterior  part 
of  the  bulging  due  to  the  heart,  and  the  anterior  border 
of  the  inferior  caval  elevation.  Arching  over  the  root  of 
the  lung  is  a  curved  ridge,  due  to  the  upper  part  of  the 
vena  azygos,  as  it  passes  anteriorly  to  join  the  superior  cava. 
Above  the  vena  azygos  and  posterior  to  the  superior  cava,  the 
right  lateral  surface  of  the  trachea,  or  main  air  tube,  may 
be  seen  or  felt  in  the  superior  mediastinal  region,  and, 
descending  obliquely  across  it,  from  above  downwards  and 
posteriorly,  the  right  vagus  nerve  can  be  palpated  or  seen. 
Posterior  to  the  root  of  the  lung  and  to  the  bulging  due  to 
the  heart,  the  oesophagus  may  be  recognised  in  the  posterior 
mediastinal  area,  either  by  touch  or  sight,  or  both.  Somewhat 
posterior  to  the  oesophagus  the  margin  of  the  ascending 
portion  of  the  vena  azygos  may  be  noted,  and  still  further 
posteriorly  are  the  bodies  of  the  vertebrae  and  the  posterior 
parts  of  the  ribs.  Crossing  the  bodies  of  the  vertebrae  trans- 
versely the  right  intercostal  vessels  may  be  visible  or  they 
may  be  felt,  and,  descending  along  the  line  of  the  heads 
of  the  ribs,  the  ganglionated  trunk  of  the  sympathetic  can  be 
recognised  by  touch,  if  not  by  sight. 

The  dissectors  should  examine  next  the  mediastinum  and 
the  posterior  wall  of  the  thorax  on  the  left  side  (see  Figs. 
8,  II,  and  13). 

By  inspection  and  palpation  they  will  easily  recognise  the 
positions  of  the  larger  and  more  important  structures.  Below 
and  anterior  to  the  root  of  the  lung  the  mediastinal  pleura  is 
bulged  much  more  laterally  on  the  left  than  on  the  right 
side  by  the  heart  covered  by  the  pericardium.  Arching 
posteriorly  and  to  the  left,  over  the  root  of  the  lung,  in  the 
superior  mediastinal  area,  is  the  arch  of  the  aorta,  and  from 
its  posterior  end  the  descending  aorta  runs  downwards,  in  the 
posterior  mediastinal  area,  first  posterior  to  the  root  of  the 
lung,  and  then  posterior  to  the  heart  but  separated,  in  part, 
from  the  latter  by  the  cesophagus,  which  diverges  towards  the 
left  side  in  the  lower  part  of  the  thorax.  Above  the  arch  of 
the  aorta  the  left  common  carotid  and  subclavian  arteries 
and  the  oesophagus  can  be  distinguished  in  the  above  order 
antero  -  posteriorly.     A   long   slender   secondary   ridge,    pro- 


^4 


THORAX 


duced  by  the  left  phrenic  nerve  and  the  accompanying  vessels 


Scalenus  anterior    p       j 

Brachial  nerves i 

Left  subclavian  artery 

Left  subclavian  vein 

Left  subclavian  artery- 
Left  vagus  nerve __/_^ 

Left  common 

carotid  artery    / 
Left  innominate  vein       ^ 
Internal  mammary 
artery 
Phrenic  nerve  and 
accompanying 
artery 

Pulmonary 
artery 

Heart  and 
pericardium 


1  horacic  duct 

("Fsophagu* 

K(  current  nerve 


\ortic  arch 


Left  pulmon- 
ary artery 

Left  bronchus 


Left  pulmon- 
ary veins 

Cut  edge  of 

parietal 

pleura 

Descending 

thoracic 

aorta 

Ligamentum 

pulmonis 

(cut) 

(Esophagus 


Diaphragm 


Fig.  II. — The  Left  Pleural  Chamber  opened  up  by  the  removal  of  its  lateral 
wall.  The  lung  has  been  taken  away  and  a  window  has  been  made 
into  the  superior  mediastinum  by  the  removal  of  a  portion  of  the  medias- 
tinal pleura.  Several  of  the  structures  which  form  the  mediastinal 
partition  are  seen  shining  through  the  mediastinal  pleura  which  is  in  situ. 


THORACIC  CAVITY  25 

descends  along  the  line  of  the  common  carotid  artery,  crosses 
the  arch  of  the  aorta,  and  then  continues  along  the  side 
of  the  pericardium.  Above  the  aortic  arch,  and  posterior  to 
the  ridge  caused  by  the  phrenic  nerve,  the  left  vagus  nerve 
can  be  seen  or  felt,  as  it  runs  downwards  along  the  anterior 
border  of  the  subclavian  artery,  and  then  downwards  and 
posteriorly  across  the  arch  of  the  aorta,  to  disappear  posterior 
to  the  root  of  the  lung.  Posterior  to  the  descending  aorta  the 
sympathetic  trunk  of  the  left  side  can  be  seen  or  palpated  as 
it  descends  along  the  line  of  the  heads  of  the  ribs. 

Anterior  to  the  pericardium  and  the  aortic  arch  and  its 
branches,  the  mediastinal  pleura  passes  forwards  to  the  back  of 
the  sternum  in  contact  with  the  pleura  of  the  opposite  side. 

When  the  inspection  and  palpation  of  the  structures 
lying  in  relation  with  the  mediastinal  and  posterior  parts  of 
the  costal  pleura  is  satisfactorily  completed,  the  greater  part 
of  the  pleura  should  be  removed  on  both  sides. 

Dissection. — Make  a  longitudinal  incision  through  the  mediastinal  pleura 
immediately  anterior  to  the  phrenic  nerve  and  a  similar  incision  posterior 
to  the  nerve. 

From  the  anterior  longitudinal  incision  an  incision  should  be  carried 
anteriorly,  at  the  level  of  the  middle  of  the  root  of  the  lung,  and  from 
the  posterior  longitudinal  incision  another  cut  should  be  carried  posteriorly 
to  the  front  of  the  root  of  the  lung  and  then  along  its  anterior 
surface.  Then  the  root  of  the  lung  should  be  turned  anteriorly  and 
an  incision  should  be  made  on  its  posterior  surface  parallel  with  that 
already  made  on  the  anterior  surface.  This  incision  should  be  carried 
posteriorly  from  the  root  of  the  lung  across  the  posterior  part  of  the  wall 
of  the  mediastinum,  and  then  laterally,  across  the  posterior  wall  of  the 
thorax.  When  the  incisions  are  completed  four  flaps  will  be  marked  out, 
two  anterior  and  two  posterior. 

The  upper  anterior  flap  on  the  right  side  must  be  turned  anteriorly  to  the 
level  of  the  anterior  border  of  the  superior  vena  cava,  where  it  may  be 
cut  away,  the  portion  of  the  pleura  extending  from  the  superior  vena  cava 
to  the  sternum  being  left  in  situ.  The  upper  anterior  flap  on  the  left 
side  should  be  turned  anteriorly  to  the  anterior  part  of  the  arch  of  the  aorta 
and  the  anterior  surface  of  the  upper  part  of  the  pericardium  where  it 
should  be  cut  away,  the  part  extending  further  forwards  to  the  sternum 
being  left  in  position.  The  lower  anterior  flap  on  each  side  must  also  be 
turned  anteriorly  till  the  anterior  part  of  the  pericardium  is  reached.  There 
it  may  be  cut  away,  but  the  portion  of  pleura  extending  from  the  peri- 
cardium to  the  sternum  should  not  be  interfered  with  at  present. 

The  posterior  flaps  on  each  side  should  be  completely  removed,  care 
being  taken  to  avoid  injury  to  any  of  the  structures  which  they  cover. 

When  the  pleura  has  been  removed,  both  dissectors  should  study  care- 
fully the  structures  exposed  on  each  side,  commencing  with  the  right 
side. 


2  6  THORAX 

Contents  of  the  Mediastinum  and  the  Structures  of  the 
Posterior  Wall  of  the  Thorax  seen  from  the  Right  Side. — 

After  the  pleura  has  been  removed  from  the  right  side  of  the 
thorax  and  the  extra-pleural  tissue  has  been  dissected  away, 
the  following  structures  are  exposed.  Below  and  anterior  to 
the  root  of  the  lung  is  the  pericardium.  Entering  the  peri- 
cardium below  and  posteriorly  is  the  thoracic  part  of  the  inferior 
vena  cava,  and  entering  the  upper  part  is  the  superior  vena 
cava.  The  upper  end  of  the  superior  vena  cava  is  continuous 
with  the  right  innominate  vein,  which  lies  posterior  to  the 
sternal  end  of  the  first  costal  cartilage.  Arching  over  the  root 
of  the  lung,  to  join  the  superior  vena  cava,  is  the  terminal  part 
of  the  azygos  vein.  Above  the  azygos  vein  and  posterior  to 
the  superior  vena  cava  are  parts  of  the  trachea,  the  right  vagus 
nerve,  and  the  oesophagus.  On  the  posterior  surface  of  the 
root  of  the  lung  is  the  posterior  pulmonary  plexus,  formed  by 
the  vagus  nerve,  and  posterior  to  the  lung  root  is  the  vena 
azygos.  At  a  lower  level,  posterior  to  the  pericardium,  the 
right  margin  of  the  oesophagus  will  be  found  anterior  to  the 
vena  azygos.  Lateral  to  the  vena  azygos,  on  the  sides  of  the 
bodies  of  the  vertebrae,  lie  the  right  aortic  intercostal  arteries, 
the  accompanying  veins,  and  the  splanchnic  nerves.  Still 
more  laterally,  on  the  line  of  the  heads  of  the  ribs,  runs  the 
sympathetic  trunk,  and  beyond  the  sympathetic  trunk  are  the 
intercostal  spaces  and  their  contents. 

After  the  various  parts  mentioned  above  have  been  located 
and  defined,  the  dissectors  should  thoroughly  clean  the 
sympathetic  trunk  and  its  branches  and  communications. 
In  the  upper  part  of  the  thorax  the  trunk  runs  along  the 
heads  of  the  ribs,  but  in  the  lower  part  it  attains  a  more 
anterior  position. 

The  Thoracic  Portion  of  the  Sympathetic  Trunk. — This  is 
continuous  above  with  the  cervical  portion  and  below  with 
the  abdominal  portion.  It  has  the  appearance  of  a  knotted 
cord.  The  knots  are  ganglia,  which  consist  of  nerve  cells  and 
fibres.  The  intermediate  parts  of  the  trunk  consist  of  nerve 
fibres  alone.  There  are  usually  eleven  ganglia,  and,  as 
a  rule,  each  ganglion  lies  opposite  the  head  of  a  rib,  but 
the  first  is  opposite  the  medial  end  of  the  first  intercostal 
space,  or  anterior  to  the  neck  of  the  first  rib,  and,  as  the 
trunk  inclines  anteriorly  below,  one  or  two  of  the  lower 
ganglia  lie  on  the  bodies  of  the  lower  thoracic  vertebrae. 


THORACIC  CAVITY 


27 


Branches. — These    may    be    divided    into    two    groups- 
(i)  Lateral;  (2)  Medial 


Scalenus  niedius 
Scalenus  anterior 

Brachial  plexus 


Cut  edge  of  costal  part 
of  parietal  pleura 

Second  right  aortic 
intercostal  artery 


Vena  azj'gos 
Sympathetic  trunk 
End  of  right 
bronchial  vein 
Branch  of  pul- 
monary artery 
Eparterial  branch 
of  bronchus 
Posterior  pul- 
monary plexus 


Hyparterial  part 
of  bronchus 

Lower  right  pul- 
monary vein 

Sulcus  terminalis 
of  right  atrium 


Great  splanchnic    , 
nerve 


Inferior  vena 
cava 


Smjill  splanchnic 
nerve 


Right  phrenic  nerve 

Right  common  carotid  artery 

Right  subclavian  artery 

Right  subclavian  vein 
H —  First  rib 

(Esophagus 

Trachea 

-  Right  vagus  nerve 
Right  phrenic  nerve 


Cut  edge  of  costal  part 
of  parietal  pleura 

Superior  vena  cava 


Internal  mam- 
mary artery 
Cut  edge  of  peri- 
cardial part  of 
parietal  pleura 
Cut  edge  of  peri- 
cardium 

Right  atrium 


Diaphragm 


Fig.  12.— Dissection  of  Thorax  from  right  side  showing  the  constituent  parts 
of  the  middle,  superior,  and  posterior  mediastina. 

(i)  Lateral  Branches. — From  each  gangUon  two  branches 
pass  laterally  into  the  adjacent  intercostal  space,  where  they 


2  8  THORAX 

join  the  corresponding  intercostal  nerve.  One  of  these 
branches,  called  the  white  root  of  the  ganglion,  contains 
medullated  fibres  which  are  passing  from  the  medulla  spinalis 
(O.T.  spinal  cord)  through  the  intercostal  nerve  to  the 
ganglion.  The  other,  the  grey  root,  consists  of  non-medullated 
fibres  which  are  passing  from  the  cells  of  the  ganglion  to  the 
nerve.  Some  of  these  fibres  are  distributed  with  the  branches 
of  the  nerve,  and  others  run  medially,  along  the  intercostal 
nerve,  to  the  spinal  nerve  trunk,  whence  some  are  distributed 
by  the  posterior  branch  and  others  pass  more  medially  to 
the  membranes  of  the  medulla  spinalis. 

(2)  Medial  Branches.  —  (a)  Pulmonary ;  {h)  Aortic ;  (c) 
Splanchnic.  {a)  The  pulmonary  branches  arise  from  the 
second,  third,  and  fourth  ganglia.  They  run  anteriorly  to  the 
posterior  surface  of  the  root  of  the  lung.  There  they  com- 
municate with  branches  of  the  vagus,  forming  a  plexus  called 
the  posterior  pulmonary  plexus,  {b)  The  aortic  branches  are 
fine  filaments  which  arise  from  the  upper  five  ganglia  and  pass 
to  the  coats  of  the  aorta ;  the  dissector  will  rarely  be  able  to 
trace  them  in  an  ordinary  dissection,  {c)  The  splanchnic 
branches  arise  from  the  sixth  to  the  last  ganglion,  and  they  run 
together  to  form  three  distinct  nerves — the  greater,  the  lesser, 
and  the  lowest  splanchnic  nerves,  which  are  all  destined  for 
the  abdominal  viscera. 

Nervus  Splanchnicus  Major. — This  nerve  is  formed  by  the 
union  of  four  or  five  roots  derived  from  the  sixth  to  the  tenth 
ganglia,  or  from  the  portions  of  the  trunk  between.  It 
passes  downwards,  on  the  bodies  of  the  vertebrae,  pierces  the 
diaphragm,  and  terminates  in  the  coeliac  (O.T.  semilunar) 
ganglion  of  the  same  side  in  the  abdomen. 

Opposite  the  last  thoracic  vertebra  there  is  frequently  a  small  ganglion 
upon  the  greater  splanchnic  nerve,  or  connected  with  it ;  from  this  ganglion 
branches  are  distributed  to  the  aorta,  where  they  communicate  with  their 
fellows  of  the  opposite  side. 

Nervus  Splanchnicus  Minor. — The  small  splanchnic  nerve 
arises  by  two  roots  either  from  the  ninth  and  tenth,  or  from 
the  tenth  and  eleventh  ganglia.  It  also  pierces  the  crus  of 
the  diaphragm  and  ends  in  the  coeliac  ganglion. 

Nervus  Splanchnicus  Imus. — The  lowest  splanchnic  nerve  is 
a  minute  branch  which  springs  from  the  last  thoracic  ganglion. 
It  is  frequently  absent,  but  when  it  is  present  it  pierces 
the  crus  of  the  diaphragm  and  ends  in  the  renal  plexus. 


THORACIC  CAVITY  29 

Dissection. — When  the  study  of  the  thoracic  portion  of  the  sympathetic 
trunk  and  its  branches  is  completed  the  posterior  parts  of  the  inter- 
costal spaces  should  be  cleaned  and  examined.  The  internal  intercostal 
muscles  will  be  seen  passing  as  far  medially  as  the  angles  of  the  ribs.  In 
some  cases  fibres  with  the  same  direction  as  those  of  the  internal  intercostal 
muscles  will  be  found  descending  from  one  rib  to  the  second  or  third 
below,  across  the  pleural  surfaces  of  the  intermediate  ribs.  Such  fibres 
constitute  the  subcostal  /iiicscles,  which  are  very  variably  developed  in 
different  subjects.  Sometimes  they  form  an  almost  complete  lining  for  the 
posterior  part  of  the  thoracic  wall,  and  in  other  cases  they  are  represented 
by  a  few  scattered  fibres,  or  they  are  entirely  absent. 

The  Posterior  Intercostal  Membranes  are  medial  to  the 
internal  intercostal  muscles  and  on  a  more  posterior  plane. 
Each  is  attached,  medially,  to  the  anterior  costo-transverse 
ligament,  which  passes  from  the  neck  of  the  rib  below  to  the 
lower  border  of  the  transverse  process  of  the  vertebra  above. 
Laterally,  it  is  continuous  with  the  fascial  layer  between  the 
internal  and  external  intercostal  muscles,  and  above  and 
below,  it  is  attached  to  the  adjacent  ribs.  On  the  pleural 
surface  of  the  posterior  intercostal  membrane,  in  each  space, 
lie  the  corresponding  intercostal  nerve  and  vessels  (see  Figs. 
12  and  13).  These  pass  laterally,  on  the  internal  surface 
of  the  membrane,  and  disappear  posterior  to  the  border  of 
the  internal  intercostal  muscle.  When  the  membranes  are 
removed  the  posterior  fibres  of  the  external  intercostal 
muscles  will  be  exposed,  passing  medially  as  far  as  the 
tubercles  of  the  ribs. 

After  the  posterior  parts  of  the  intercostal  spaces  and  their  contents  have 
been  fully  considered  the  vena  azygos  should  be  studied.  If  it  is  traced 
downwards,  from  above  the  root  of  the  lung,  it  will  be  found  to  disappear 
gradually  posterior  to  the  right  margin  of  the  oesophagus,  which  must  be 
raised  to  display  its  lower  portion. 

The  Vena  Azygos. — This  vein  enters  the  thorax  through 
the  aortic  aperture  of  the  diaphragm,  to  the  right  of  the  aorta 
and  thoracic  duct,  the  lower  parts  of  which  will  be  displayed 
as  the  vein  is  cleaned.  After  entering  the  thorax  the  vein 
ascends,  along  the  right  side  of  the  aorta,  from  which  it  is 
separated  by  the  thoracic  duct.  A  short  distance  above  the 
diaphragm  it  passes  more  or  less  completely  behind  the  right 
border  of  the  oesophagus.  At  the  lower  border  of  the  root 
of  the  lung  it  emerges  from  behind  the  cesophagus,  passes 
posterior  to  the  lung  root,  turns  anteriorly  above  its  superior 
border,  at  the  level  of  the  fifth  thoracic  vertebra,  and  terminates 
in  the  posterior  wall  of  the  superior  vena  cava,  immediately 
above  the   point  where   the    latter    enters    the    pericardium, 


30  THORAX 

at  the  level  of  the  second  costal  cartilage  (see  Fig.  12).  As 
it  turns  anteriorly  the  vein  lies  immediately  to  the  right  side 
of  the  oesophagus,  trachea  and  vagus  nerve. 

The  tributaries  of  the  vena  azygos  are  :  (i)  The  right 
superior  intercostal  vein  which  drains  blood  from  the 
greater  part  of  the  second  and  third  intercostal  spaces. 
(2)  The  eight  lower  intercostal  veins  and  the  subcostal  vein 
of  the  right  side.  (3)  The  vena  hemiazygos,  and  frequently 
(4)  the  vena  hemiazygos  accessoria.  Both  the  latter  enter  it 
from  the  left.  In  many  cases  the  accessory  azygos  vein  joins 
the  hemiazygos  vein.  (5)  Two  or  more  bronchial  veins  from 
the  right  lung.  (6)  Some  veins  from  the  oesophagus.  (7) 
Some  minute  pericardial  veins. 

The  vena  azygos  commences  in  the  abdomen  where  it 
anastomoses  either  with  one  of  the  upper  lumbar  veins  or 
directly  with  the  inferior  vena  cava.  Thus  it  forms  a  more 
or  less  direct  anastomosis  between  the  two  venae  cavse. 

The  intercostal  veins  and  the  accompanying  arteries  and 
nerves,  on  both  sides,  and  the  hemiazygos  and  accessory 
azygos  veins  will  be  studied  at  a  later  period  of  the  dissection 
(see  p.  108). 

Contents  of  the  Mediastinum  and  the  Structures  of  the 
Posterior  Part  of  the  Left  Half  of  the  Thorax  seen  from  the 
Left  Side. — After  the  removal  of  the  four  pleural  flaps  described 
on  p.  25  the  following  structures  are  visible  on  the  left  side 
of  the  thorax  (see  Fig.  13).  Below  and  anterior  to  the  root 
of  the  lung  is  the  pericardium,  covering  the  left  ventricle,  the 
left  atrium,  the  conus  arteriosus  of  the  right  ventricle  and  the 
pulmonary  artery.  Above  the  root  of  the  lung  is  the  arch  of 
the  aorta.  The  arch  of  the  aorta  terminates  posteriorly  in 
the  descending  aorta,  which  passes  downwards  posterior  to 
the  root  of  the  lung  and  the  pericardium,  but  it  is  separated 
from  the  lower  part  of  the  posterior  wall  of  the  pericardium 
by  the  oesophagus,  which,  at  this  level,  is  passing  towards 
the  left  side.  On  the  left  and  anterior  aspect  of  the  aortic 
arch,  from  behind  forwards,  lie  the  left  vagus  nerve,  the 
superior  cervical  cardiac  branch  of  the  left  sympathetic 
trunk,  the  inferior  cervical  cardiac  branch  of  the  left  vagus, 
and  the  left  phrenic  nerve  with  its  accompanying  vessels. 
Crossing  the  arch  obliquely,  from  behind  forwards  and 
upwards,  is  the  left  superior  intercostal  vein,  which  passes 
lateral  to  the  vagus  and  medial  to  the  phrenic  nerve.     Above 


THORACIC  CAVITY 


31 


the  arch  of  the  aorta  are  the  lower  parts  of  the  left  common 


Thyreoid  gland 

Left  common  carotid  artery 

Scalenus  anterior 

Left  subclavian  arterj' 

Left  subclavian  vein 

First  rib 

Left  innominate  vein 

Left  common  carotid  artery 
Left  subclavian  artery 

Left  phrenic  nerve 

Left  vagus  nerve 

Cut  edge  of  pleura 

Cut  edge  of  peri- 
cardium and  pleura 

Pulnionarj'  artery 


Conus  arteri- 
osus of  right 
ventricle 

nter\'entricular 
branch  of  left 

:oronarj'  arterj- 

Cut  edge  of 
pleura 

Cut  edge  of 
pericardium 


Left  ventricle 


Brachial  plexus 


Thoracic  duct 
First  left  aortic 
intercostal  artery 
Qisophagus 

Sympathetic  trunk 

Left  superior 
intercostal  vein 
Arch  of  aorta 


Left  pulmonary  artery 

Upper  left 
pulmonarj-  vein 

Left  bronchus 


Left  auricle  (O.T. 
auricular  appendage) 
Lower  left 
pulmonary  vein 

Circumflex  branch 
of  left  coronary 
artery 


Great  splanchnic 


Diaphragm 


Fig.  13. — Dissection  of  Thorax  from  left  side  showing  the  constituent  parts 
of  the  superior,  middle,  and  posterior  mediastina. 

carotid  and  left  subclavian  arteries,  and  posterior  to  the  latter 
lies  the  oesophagus,  with  the  thoracic  duct  running  along  its 
left  lateral  border. 


32  THORAX 

Posterior  to  the  descending  aorta  are  the  left  aortic  inter- 
costal arteries,  the  accompanying  veins,  and  the  splanchnic 
nerves ;  and  still  more  posteriorly  and  laterally  lie  the 
sympathetic  trunk  of  the  left  side  and  the  left  intercostal 
spaces  and  their  contents. 

Dissection. — After  the  structures  exposed  by  the  removal  of  the  left 
pleura  have  been  located,  the  dissectors  should  direct  their  attention  to  the 
sympathetic  trunk  and  its  branches  and  communications.  The  arrange- 
ment of  these  is  exactly  similar  to  that  already  described  on  the  right  side 
(see  p.  26),  When  the  dissectors  have  confirmed  this  statement  they 
should  turn  to  the  left  subclavian  artery,  which  is  the  most  posterior  of  the 
three  great  branches  which  spring  from  the  arch  of  the  aorta.  Clean  this 
vessel  without  disturbing  the  vagus  nerve,  which  descends  along  its  anterior 
border.  Afterwards  clean  the  part  of  the  aortic  arch  which  lies  posterior  to 
the  vagus  nerve,  and  the  descending  aorta.  Whilst  cleaning  the  arch  avoid 
injuring  the  left  superior  intercostal  vein,  and,  as  the  descending  aorta  is 
being  cleaned,  endeavour  to  preserve  any  of  the  aortic  branches  of  the 
sympathetic  which  may  have  been  found  previously  during  the  examination 
of  the  sympathetic  trunk. 

As  the  aorta  is  cleaned  the  left  border  of  the  lower  part  of  the 
oesophagus  will  be  brought  more  clearly  into  view,  but  the  dissector  must 
not  attempt  to  clean  the  oesophagus  at  this  stage. 

After  the  descending  portion  of  the  aorta  is  cleaned,  the  left  aortic 
intercostal  arteries  should  be  examined.  They  are  nine  in  number  ;  they 
emerge  from  the  posterior  aspect  of  the  aorta,  and  they  all  pass  medial  to 
the  sympathetic  trunk  as  they  approach  the  intercostal  spaces.  The  upper 
arteries  ascend  very  obliquely  to  gain  their  proper  spaces.  Accompanying 
the  arteries  are  the  corresponding  veins.  The  lower  veins  pass,  posterior  to 
the  aorta,  to  their  terminations  in  the  hemiazygos  and  accessory  hemiazygos 
veins,  and  will  be  more  fully  studied  at  a  later  stage  ;  but  the  veins  from 
the  second  and  third  spaces  unite  into  a  trunk  called  the  left  superior 
intercostal  vein. 

The  Left  Superior  Intercostal  Vein. — This  vein  is  formed 
by  the  intercostal  veins  from  the  second  and  third  intercostal 
spaces  of  the  left  side,  and  it  not  uncommonly  receives  a 
communication  from  the  first  and  fourth  spaces.  It  descends 
along  the  medial  border  of  the  first  left  aortic  intercostal 
artery  to  the  posterior  end  of  the  aortic  arch,  there  it  turns 
anteriorly,  along  the  left  side  of  the  aortic  arch,  and,  passing 
at  the  same  time  obliquely  upwards,  it  crosses  lateral  to  the 
left  vagus  and  medial  to  the  left  phrenic  nerve.  At  a  later 
period  of  the  dissection  it  will  be  traced  to  its  termination 
in  the  left  innominate  vein. 

Dissection. — After  the  left  superior  intercostal  vein  has  been  secured 
and  studied,  the  dissectors  should  clean  the  region  posterior  to  the  left 
subclavian  artery,  and  expose  thoroughly  the  left  border  of  the  oesophagus, 
as  that  tube  lies  in  the  superior  mediastinum,  and  the  upper  part  of  the 
thoracic  portion  of  the  thoracic  duct,  which  runs  along  the  border  of  the 
oesophagus. 


THORACIC  CAVITY  33 

After  this  stage  of  the  dissection  is  completed,  the  dissectors 
should  examine  the  triangular  interval  between  the  left  phrenic 
and  left  vagus  nerves  in  the  upper  part  of  the  thorax.  Com- 
mencing above,  they  should  follow  the  vagus  nerve  down- 
wards ;  just  before  it  reaches  the  lower  border  of  the  aortic 
arch,  it  gives  off  a  very  distinct  branch  which  turns  round 
the  lower  border  of  the  arch.  This  is  the  important  recurrent 
nerve  which  supplies  the  majority  of  the  intrinsic  muscles  of 
the  larynx  of  the  same  side.  Immediately  anterior  and 
medial  to  the  point  where  the  recurrent  nerve  turns  beneath 
the  arch,  a  very  distinct  fibrous  cord  must  be  defined.  It 
connects  the  arch  with  the  upper  border  of  the  left  pulmonary 
artery  close  to  its  origin.  This  is  the  Ugamentiim  arferiosu7n, 
and  it  is  the  remains  of  the  ductus  arteriosus,  through  which 
blood  passed  from  the  pulmonary  artery  to  the  aorta  during 
foetal  life.  When  this  has  been  secured  the  areolar  tissue 
between  the  phrenic  and  vagus  nerves  must  be  carefully 
removed.  In  this  tissue  two  small  nerves  wall  be  found 
which  run  downw^ards,  parallel  with  the  vagus,  across  the  arch 
of  the  aorta.  The  one  next  the  vagus  is  the  superior  cervical 
cardiac  branch  of  the  left  sympathetic,  and  the  one  next  the 
phrenic  is  the  inferior  cervical  cardiac  branch  of  the  left 
vagus.  When  these  nerves  are  followed  downwards  they 
will  be  found  to  end  in  the  superficial  cardiac  plexus,  which 
lies  in  the  areolar  tissue  below  the  aortic  arch  and  to  the  right 
of  the  hgamentum  arteriosum. 

Dissection. — After  the  pericardium  has  been  cleaned,  incisions  should 
be  made  through  it  on  each  side,  and  the  flaps  formed  should  be  turned 
aside  so  that  the  dissectors  may  make  themselves  familiar  ^\dth  the  relation- 
ships of  the  heart  to  the  mediastinal  portions  of  the  pleural  sacs.  Two 
longitudinal  incisions  must  be  made  on  each  side,  one  anterior  and  one 
posterior  to  the  longitudinal  strip  of  pleura  left  on  the  lateral  surface  of  the 
phrenic  nerve  (see  Pigs.  12  and  13).  On  the  right  side  the  incisions  should 
commence  at  the  level  of  the  upper  pulmonary  vein.  On  the  left  side 
the  anterior  incision  should  begin  at  the  lower  border  of  the  aortic  arch 
and  the  posterior  at  the  level  of  the  left  pulmonary  artery  (see  Fig.  13). 
On  both  sides  the  longitudinal  incisions  must  descend  to  the  lower  border 
of  the  pericardium.  On  both  sides  incisions  should  be  carried  anteriorly 
from  the  upper  and  lower  ends  of  the  anterior  longitudinal  incision  to  the 
line  along  which  the  mediastinal  pleura  was  left  attached  to  the  anterior 
surface  of  the  pericardium  (see  Figs.  12  and  13).  From  the  upper  end  of 
the  posterior  longitudinal  incision  on  the  right  side  a  cut  should  be  made 
downwards  and  posteriorly  along  the  anterior  aspect  of  the  root  of  the  lung 
to  the  upper  end  of  the  inferior  vena  cava  (see  Y\g.  12). 

From  the  upper  end  of  the  posterior  longitudinal  incision  on  the  left  side 
an  oblique  cut  must  be  made  downwards  and  posteriorly,  along  the  line  of 

VOL.  II — 3 


34  THORAX 

the  anterior  surface  of  the  root  of  the  left  lung.  When  the  incisions  have 
been  made,  the  anterior  flaps  can  be  turned  anteriorly  and  the  posterior  flaps 
downwards.  None  of  the  flaps  must  be  removed,  for  it  will  be  necessary 
to  replace  them  in  position  at  a  later  stage  of  the  dissection. 

When  the  flaps  marked  out  by  these  incisions  are  turned  aside  the 
dissectors  will  find  that,  on  the  right  side,  they  have  exposed  the  greater 
part  of  the  right  atrium  (see  Fig.  12).  They  should  note  that  the  area  of 
the  atrium  which  is  exposed  is  separated  into  two  parts  by  a  vertical  sulcus, 
the  stdcus  ter??tinalis,  which  runs  from  the  anterior  face  of  the  cardiac  end 
of  the  superior  vena  cava  to  the  anterior  aspect  of  the  terminal  part  of  the 
inferior  vena  cava.  This  sulcus  divides  the  atrium  into  a  posterior  part, 
the  sinus  venosus,  and  an  anterior  part,  the  atrium  proper,  whose  upper 
and  anterior  part  is  prolonged  medially  to  the  anterior  surface  of  the  heart. 
On  the  left  side  the  greater  part  of  the  heart  exposed  by  the  reflection  of 
the  pericardial  flaps  is  the  left  ventricle,  but  in  the  upper  part  of  the 
area  the  auricle  (O.T.  auricular  appendage)  of  the  left  atrium  is  seen. 
Anterior  to  it  lie  the  stem  of  the  pulmonary  artery  and  the  upper  part 
of  the  anterior  portion  of  the  right  ventricle.  A  line  of  fat,  in  which  lie 
the  interventricular  branch  of  the  left  coronary  artery  and  the  accompany- 
ing vein,  indicates  the  position  of  the  septum  between  the  left  and  right 
ventricles  (Fig.  13). 

After  the  dissection  is  completed  and  the  dissectors  have  carefully  noted 
the  relative  positions  of  the  various  structures  which  have  been  exposed, 
they  should  proceed  to  study  the  phrenic  nerves,  which  have  been  retained  in 
position  by  the  strips  of  pleura  on  their  lateral  surfaces  (see  Figs.  12  and  13). 

Nervi  Phrenici. — Each  phrenic  nerve  arises  in  the  neck 
from  the  cervical  plexus,  receiving  fibres  from  the  third, 
fourth,  and  fifth  cervical  nerves.  It  descends  on  the  scalenus 
anterior  muscle  and,  at  the  root  of  the  neck,  passes  anterior 
to  the  subclavian  artery  and  posterior  to  the  corresponding 
vein,  but  on  the  left  side,  as  it  leaves  the  scalenus  anterior, 
it  lies  anterior  to  the  subclavian  artery  and  posterior  to  the 
commencement  of  the  innominate  vein.  As  it  enters  the 
upper  aperture  of  the  thorax  it  crosses  the  internal  mammary 
artery,  passing  from  its  lateral  to  its  medial  side,  then 
it  descends  along  the  lateral  border  of  the  mediastinum, 
anterior  to  the  root  of  the  lung,  to  the  diaphragm  where 
it  breaks  up  into  branches.  The  majority  of  the  branches 
pass  between  the  muscular  fibres  of  the  diaphragm  and, 
after  communicating  with  the  abdominal  sympathetic  nerve 
fibres  which  form  the  diaphragmatic  plexus,  they  are 
distributed  to  the  muscle  from  its  lower  surface.  The  re- 
lations of  the  phrenic  nerves  in  the  thorax  are  different 
on  the  two  sides,  and  the  left  phrenic  nerve,  as  a  whole,  is 
on  a  plane  somewhat  anterior  to  the  right. 

The  right  phrenic  nerve  descends  along  the  lateral  borders 
of  the  right  innominate  vein  and  the  superior  vena  cava  to 
the  point  where  the  latter  enters  the  pericardium,  then  along 


THORACIC  CAVITY  35 

the   side   of   the  pericardium,   which   separates    it   from   the 
venous  sinus  of  the  right  atrium  (see  Fig.  12). 

The  Left  Phrenic  Nerve. — In  the  upper  part  of  the  thorax 
the  left  phrenic  nerve  runs  downwards  between  the  left 
common  carotid  and  the  left  subclavian  arteries  and,  whilst 
lying  between  them,  it  crosses  anterior  to  the  left  vagus  and 
posterior  to  the  left  innominate  vein.  In  the  lower  part  of 
.the  superior  mediastinum  it  passes  lateral  to  the  arch  of  the 
aorta  and  the  left  superior  intercostal  vein,  then,  descending 
into  the  middle  mediastinum,  it  lies  at  first  anterior  to  the 
root  of  the  left  lung,  and  afterwards  it  runs  downwards  along 
the  side  of  the  pericardium,  which  separates  it  from  the 
anterior  part  of  the  left  atrium  and  from  the  lateral  part  of 
the  left  ventricle  of  the  heart. 

The  left  phrenic  nerve  is  longer  than  its  fellow  of  the  right  side,  partly 
on  account  of  the  lower  position  of  the  diaphragm,  and  partly  on  account 
of  the  greater  projection  of  the  heart  on  the  left  side. 

Branches  of  the  Phrenic  Nerves. — The  main  distribution 
of  the  phrenic  nerves  is  to  the  diaphragm,  but  some  minute 
sensory  twigs  are  given  off  by  each  nerve  to  the  pericardium 
and  to  the  pleura.  The  student  should  note  the  great  import- 
ance of  the  phrenic  nerves.  They  are  the  nerves  of  supply 
to  the  diaphragm,  which  is  the  chief  muscle  of  respiration. 

Pulmones. ^-Before  proceeding  to  the  further  dissection 
of  the  constituent  parts  of  the  mediastinum,  the  dissectors 
should  study  the  lungs  which  they  previously  removed.  The 
lungs  are  two  soft,  comparatively  light,  spongy  organs  placed 
one  on  either  side  of  the  mediastinum.  The  weight  of  the 
right  lung,  when  it  is  filled  with  an  average  amount  of  blood, 
is  22  oz.  and  that  of  the  left  20  oz.  When  the  thorax  is 
opened  the  lungs  collapse  to  about  one-third  of  their  original 
bulk  (unless  they  have  been  hardened  in  situ),  and  it  is 
difficult  for  the  student  to  realise  their  proper  size  and 
shape  until  they  are  distended  to  their  original  dimensions 
with  the  aid  of  the  bellows  (see  p.  16). 

When  healthy  and  sound,  the  lungs  lie  free  within  the 
cavity  of  the  chest,  and  are  attached  only  by  their  roots  and 
by  their  pulmonary  ligaments.  It  is  rare,  however,  that  a 
healthy  lung  is  seen  in  the  dissecting-room,  for  adhesions  be- 
tween the  visceral  and  parietal  portions  of  the  pleura,  due  to 
pleurisy,  are  generally  present.  Each  lung  is  accurately 
adapted  to  the  space  in  which  it  lies,  and,  when  hardened 

II — 3  a 


36 


THORAX 


in  situ,  it  bears  on  its  surface  impressions  and  elevations 
which  are  an  exact  counterpart  of  the  inequahties  of  the 
structures  with  which  its  surfaces  are  in  contact  at  the 
moment  of  fixation. 

In  the  natural  condition  each  lung  resembles  half  a  cone, 
and  it  presents  for  examination  an  apex^  a  base,  a  costal 
surface,  a  medial  surface.  An  anterior  and  a  posterior  border 
separate  the  medial  from  the  lateral  surface ;  and  an  inferior 
or  basal  border  separates  the  base  from  the  medial  and  lateral 

Trachea 


Subclavian  sulcu 
Groove  caused 
by  the  first  nb 


Subclavian  sulcus 

Groove  caused 
by  the  first  rib 


Lower  lobe 


Cardiac  notch 


Lower  lobe 


Fig.  14. — The  Trachea,  Bronchi,  and  Lungs  of  a  Child,  hardened 
by  formalin  injection. 

surfaces.  The  apex  rises  into  the  root  of  the  neck  for  one 
and  a  half  inches  above  the  level  of  the  anterior  part  of  the 
first  rib,  and  it  is  crossed  by  the  subclavian  artery,  which 
makes  a  groove  upon  the  anterior  border,  a  short  distance 
below  the  summit,  although  the  artery  is  separated  from  the 
lung  by  the  membranous  cervical  diaphragm  (Sibson's  fascia), 
and  by  the  pleura. 

The  base  of  each  lung  has  a  semilunar  outline  and  is 
adapted  to  the  upper  surface  of  the  diaphragm.  Consequently 
it  is  deeply  hollowed  out,    and,  as  the  right  cupola  of  the 


THORACIC  CAVITY 


37 


diaphragm  ascends  higher  than  the  left,  the  basal  concavity 
of  the  right  lung  is  deeper  than  that  of  the  left  lung.  The 
lateral  and  posterior  parts  of  the  basal  margin  of  the  lung 
are  thin  and  sharp  and  extend  downwards  into  the  phrenico- 
costal  sinus  of  the  pleura,  which  intervenes  between  the 
diaphragm  and  the  wall  of  the  thorax.  This  margin  reaches  a 
much  lower  position  posteriorly  and  laterally  than  anteriorly, 
but  in  all  situations  it  falls  considerably  short  of  the  bottom  of 
the  sinus.  The  mediastinal  part  of  the  basal  margin,  which 
lies  along  the  lower  border  of  the  pericardium,  is  more 
rounded. 

The  diaphragm  separates  the  base  of  the  right  lung  from 


Right  vagus  nerve 

Righ 
subclavian  artery 
Right 
innominate  vein 


Fig. 


-Cervical  Domes  of  the  Pleural  Sacs,  and  parts  in  relation  to  them. 


the  upper  surface  of  the  right  lobe  of  the  liver,  and  the  base 
of  the  left  lung  from  the  left  lobe  of  the  liver,  the  stomach, 
the  spleen,  and,  in  some  cases,  from  the  left  extremity  of  the 
transverse  colon. 

The  costal  surface  of  the  lung  is  very  extensive  and  convex. 
It  lies  in  relation  with  the  costal  pleura,  which  separates  it 
from  the  ribs  and  intercostal  muscles,  the  transversus  thoracis 
and  the  sternum,  and  it  bears  the  impressions  of  the  costal 
arches. 

The  medial  surface  is  separable  into  an  2intQnor  ox  mediastinal 
portion  and  a  posterior  or  vertebral  portion.  The  vertebral 
portion  lies  against  the  sides  of  the  bodies  of  the  vertebra. 
The  mediastinal  part  is  applied  against  the  mediastinal 
partition  and  presents  markings  which  are  the  exact  counter- 
parts of  the  inequalities  of  the  corresponding  lateral  surface 
II— 3  & 


38 


THORAX 


of  the  mediastinum.  Thus,  it  is  deeply  hollowed  out  in 
adaptation  to  the  pericardium  upon  which  it  fits.  The 
pericardial  concavity  occupies  the  greater  part  of  the 
mediastinal  surface,  and,  owing  to  the  greater  projection 
of  the  heart  to  the  left  side,  it  is  much  more  extensive  in 
the  left  lung  than  in  the  right  lung. 


Groove  for  arch  of  aorta 


Left  pulmonary  artery 

Upper  left 

pulmonary  vein 

Left  bronchus 


Lower  left 
pulmonary  vein 


Pulmonary 
ligament 


Groove  for 
oesophagus 


Groove  for  left  subclavian  artery 
Groove  for  left  innominate  vein 

Groove  for  first  rib 


Groove  for  tissue  in 
mediastinum, 
thymus,  etc. 


V    Groove  for  conus 
arteriosus 


Depression  for 
left  ventricle 


Cardiac  notch 


Fig.  i6.— Medial  of  a  Left  Lung  hardened  in  situ. 

At  the  upper  and  posterior  part  of  the  pericardial  area  is 
the  hilus  of  the  lung.  This  is  a  wedge-shaped  depressed  area 
through  which  the  bronchus  and  the  pulmonary  artery  enter 
and  the  pulmonary  veins  and  lymphatics  leave  the  lung.  It 
is  surrounded  by  the  pleura  which  is  reflected  from  its  margin 
on  to  the  root  of  the  lung,  and  the  layer  of  reflected  pleura 
round  the  hilus  is  continuous,  below,  with  the  pulmonary 
ligament.  The  portion  of  the  pericardial  area  anterior  to  the 
upper  part  of  the  hilus  of  the  left  lung  corresponds  with  the 


THORACIC  CAVITY 


39 


position  of  the  conus  arteriosus  and  the  stem  of  the  puhnonary 
artery,  and  the  same  portion  of  the  pericardial  area  on  the 
right  side  corresponds  with  the  position  of  the  lower  part  of 
the  superior  vena  cava  posteriorly  and  with  the  ascending 
aorta  anteriorly  (Fig.  17).      Below  and  posterior  to  the  lower 


Groove  for  right  subclavian  artery  .^ 

Groove  for  lower  end  of  internal  — ^ 
jugular  vein 

Groove  for  ist  rib 


Groove  for  superior 
vena  cava 

Groove  for  ascending 
aorta 


Depression  for 
right  atrium 


-  QEsophageal  area 
Tracheal  area 


Groove  for  azygos 
vein 


Groove  for 
az^^'gos  vein 


Groove  for 
oesophagus 


Groove  for  in- 
ferior vena  cava 
Pulmonary 
ligament 


Fig.  17. — The  Medial  Surface  of  a  Right  Lung  hardened  in  situ. 


and  posterior  part  of  the  pericardial  area  on  the  right  lung  is  a 
secondary  depression  due  to  the  upper  part  of  the  inferior 
vena  cava.  Posterior  to  the  pericardial  area  and  the  hilus 
there  is  a  narrow  strip  of  the  mediastinal  surface  of  the  lung 
which  is  in  relation  with  the  lateral  wall  of  the  posterior 
mediastinum.  On  the  right  lung  this  portion  of  the 
surface  presents  a  longitudinal  depression  which  corresponds 
with  the  right  border  of  the  oesophagus,  and  more  posteriorly 
at  the  upper  part  there  may  be  a  groove  caused  by  the  vena 


40  THORAX 

azygos.  The  left  lung  in  the  corresponding  situation  is 
marked  by  a  deep  longitudinal  groove  which  is  produced 
by  the  contact  of  the  lung  with  the  descending  thoracic 
aorta ;  and,  close  to  the  base,  a  small  triangular  area,  anterior 
to  the  aortic  groove,  lies  in  relation  with  the  left  border  of 
the  lowest  part  of  the  thoracic  portion  of  the  oesophagus. 

The  portion  of  the  mediastinal  surface  which  lies  above 
the  hilus  and  pericardial  hollow  is  applied  to  the  lateral 
aspect  of  the  superior  mediastinum  and  the  markings  upon 
it  are  different  on  the  two  sides.  On  the  left  side  a  broad 
deep  groove,  caused  by  the  aortic  arch,  curves  over  the  hilus 
and  becomes  continuous  posteriorly  with  the  aortic  groove 
on  the  posterior  mediastinal  area.  From  this  arched  groove 
a  sharply  cut  sulcus,  caused  by  the  left  subclavian  artery, 
ascends  on  the  medial  side  of  the  apex  and,  turning  laterally 
above,  it  crosses  the  anterior  border  of  the  apex  a  short 
distance  below  the  summit.  Immediately  anterior  to  the 
subclavian  sulcus  the  medial  surface  of  the  apex  is  occasion- 
ally marked  by  a  shallow  sulcus  caused  by  the  lateral  margin 
of  the  left  innominate  vein,  and  more  inferiorly  its  anterior 
margin  is  depressed  by  the  first  rib.  That  portion  of  the 
surface  which  lies  posterior  to  the  subclavian  sulcus  is 
separated  by  areolar  tissue  from  the  oesophagus. 

On  the  right  lung  also  a  curved  sulcus  arches  over  the 
hilus.  It  is  caused  by  the  vena  azygos,  as  it  passes  anteriorly 
to  join  the  superior  vena  cava.  This  groove  is  much  narrower 
and  less  distinct  than  the  sulcus  on  the  left  lung  due  to  the 
aortic  arch.  From  the  anterior  end  of  the  sulcus  for  the 
azygos  vein  a  broad  shallow  sulcus  passes  upwards  to  the 
lower  and  anterior  part  of  the  apex.  This  is  produced  by 
the  superior  vena  cava  and  the  innominate  vein,  and  in  some 
cases  it  is  prolonged  to  the  upper  part  of  the  apex  by  a 
slight  longitudinal  depression  due  to  the  pressure  of  the 
internal  jugular  vein.  Arching  laterally,  across  the  upper 
part  of  the  anterior  aspect  of  the  apex,  there  is  a  shallow  groove 
produced  by  the  right  subclavian  artery.  Posterior  to  the  sulcus 
for  the  innominate  vein,  the  medial  surface  of  the  apex  lies  in 
relation  with  the  right  side  of  the  trachea,  and  still  further 
posteriorly  it  is  either  in  relation  with  the  right  lateral  border 
of  the  superior  mediastinal  part  of  the  oesophagus,  or  it  is 
separated  from  it  by  a  mass  of  areolar  tissue. 

The  anterior   and   posterior   borders   of  the  lung   are   in 


THORACIC  CAVITY  41 

marked  contrast  with  each  other.  The  anterior  is  compara- 
tively short  and  thin  and  it  extends  medially  into  the  costo- 
mediastinal  sinus  of  the  pleura,  which  lies  posterior  to  the 
sternum  and  the  costal  cartilages.  It  commences  at  the  apex, 
curves  downwards,  anteriorly  and  medially,  posterior  to  the 
sterno-clavicular  articulation,  to  the  lower  border  of  the 
manubrium  sterni,  and  then  it  descends  vertically  to  the  base. 
Immediately  below  the  highest  point  of  the  apex  it  is  grooved 
by  the  subclavian  artery  on  each  side,  and  on  the  left  side  it 
presents  a  cardiac  notch  at  the  levelof  the  fifth  costal  cartilage. 
The  posterior  border  is  rounded  and  indistinct.  It  descends 
from  the  apex  to  the  base,  along  the  line  of  the  articulations  of 
the  heads  of  the  ribs  with  the  bodies  of  the  vertebras,  and 
it  is  much  longer  than  the  anterior  border. 

Lobes  of  the  Lungs. — The  left  lung  is  divided  into  two 
lobes  by  a  long,  deep  oblique  fissure  which  penetrates  its 
substance  to  within  a  short  distance  of  the  hilus.  This  fissure 
begins  above  at  the  posterior  border,  about  tw^o  and  a  half 
inches  below  the  apex,  at  the  level  of  the  vertebral  end  of 
the  third  rib,  which  corresponds  wdth  the  medial  end  of  the 
spine  of  the  scapula.  It  is  continued  on  the  lateral  surface, 
in  a  somewhat  spiral  direction,  downwards  and  anteriorly  till  it 
cuts  the  inferior  margin  opposite  the  lateral  part  of  the  costal 
cartilage.  The  upper  lobe  of  the  lung  lies  above  and  anterior 
to  this  cleft.  It  is  conical  in  form,  with  an  oblique  base. 
The  apex  and  the  whole  of  the  anterior  border  belong  to  it. 
The  lower  lobe,  somewhat  quadrangular,  is  more  bulky  than  the 
upper,  and  Hes  below  and  posterior  to  the  fissure  ;  it  comprises 
the  entire  base  and  the  greater  part  of  the  thick  posterior 
border. 

In  the  right  lung  there  are  two  fissures  subdividing  it  into 
three  lobes.  The  oblique  fissure  is  very  similar  in  its  position 
and  relations  to  the  fissure  in  the  left  lung,  but  it  is  more 
vertical  in  direction.  It  separates  the  lower  lobe  from  the 
upper  and  middle  lobes.  The  second  cleft,  the  horizontal 
fissure,  begins  at  the  anterior  border  of  the  lung  at  the  level 
of  the  fourth  costal  cartilage  and  extends  horizontally  till  it 
joins  the  oblique  fissure.  The  middle  or  intermediate  lobe, 
thus  cut  off,  is  wedge-shaped  in  outhne.  It  lies  between  the 
oblique  and  horizontal  fissures. 

Differences  between  the  two  Lungs. — The  dissectors  should 
particularly  note  the  following  differences  between  the  two 


42 


THORAX 


lungs  : — (i)  The  right  lung  is  slightly  larger  than  the  left,  in 
the  proportion  of  ii  to  lo.  (2)  The  right  lung  is  shorter 
and  wider  than  the  left  lung.  This  difference  is  due  to 
the  great  bulk  of  the  right  lobe  of  the  liver,  which  elevates 
the  right  cupola  of  the  diaphragm  to  a  higher  level  than 
the  left  cupola,  and  also  to  the  heart  and  pericardium,  which 
project  more  to  the  left  than  the  right,  and  thus  diminish 
the  width  of  the  left  lung.  (3)  The  anterior  sharp 
margin  of  the  right  lung  is  more  or  less  straight ;  the 
corresponding  margin  of  the  left  lung  presents,  in  its  lower 
part,   a  marked  angular  ■  deficiency  {incisura  cardiacd)  for  the 


EPARTERIAL 
BRANCH 

Of  right 
y  Bronchus 


Reflection 
/  of  pleura 


Pulmonary 
veins 


amentum  pulmonis 


Fig.  18. — The  two  Pulmonary  Roots  transversely  divided  close  to  the 
hilus  of  each  lung. 


reception  of  the  heart  and  the  pericardium.  (4)  The  right 
lung  is  subdivided  into  three  lobes,  and  the  left  lung  into  two. 
Radix  Pulmonis. — The  root  of  the  lung  is  formed  by  a 
number  of  structures  which  enter  the  lung  at  the  hilus  or 
slit  on  its  mediastinal  surface.  The  structures  which  form 
the  root  are  held  together  by  an  investment  of  pleura,  and 
they  constitute  a  pedicle  which  attaches  the  lung  to  the 
contents  of  the  mediastinum.  The  pleura  has  already  been 
removed  from  around  them,  and  now  a  more  detailed 
examination  of  the  constituent  parts  of  the  root  and  of  its 
relations    must   be    made.       The    portion    of   the    root    still 


THORACIC  CAVITY  43 

attached    to    the    mediastinum     should     be     used     for     this 
purpose. 

Dissection. — Commence  with  the  vagus  nerve  and  follow  it  downwards 
from  a  point  just  above  the  vena  azygos  on  the  right  side,  and  from  the  arch 
of  the  aorta  on  the  left,  looking  carefully  for  small  branches  which  spring 
from  its  anterior  border  and  pass  to  the  anterior  surface  of  the  root,  where 
they  communicate  with  the  twigs  from  the  sympathetic  ganglia,  and  from 
the  deep  cardiac  plexus,  to  form  the  anterior  ptdmonary  plextis,  from 
which  branches  are  distributed  to  the  walls  of  the  air  tube  and  the  blood 
vessels.  On  the  left  side  a  few  twigs  may  be  found  passing  from  the  super- 
ficial cardiac  plexus  to  the  anterior  pulmonary  plexus.  After  the  branches 
of  the  vagus  to  the  anterior  pulmonary  plexus  have  been  identified,  the 
trunk  of  the  vagus,  on  each  side,  must  be  followed  down  to  the  posterior 
surface  of  the  root  of  the  lung,  where  it  breaks  up  into  branches  which 
unite  with  twigs  from  the  corresponding  sympathetic  trunk  to  form  the 
posterior  pulmonary  plexus  (see  p.  28).  The  posterior  pulmonary  plexuses 
of  opposite  sides  are  connected  together  by  strong  branches,  which  pass 
both  anterior  and  posterior  to  the  oesophagus,  and  each  gives  branches  to  the 
walls  of  the  bronchial  tube  and  the  blood  vessels  of  the  root  of  its  own  side. 
These  various  branches  must  be  found  and  identified.  After  the  posterior 
pulmonary  plexuses  are  satisfactorily  displayed  the  bronchial  blood  vessels 
should  be  found  and  cleaned. 

Arterise  Bronchiales. — As  a  rule,  two  bronchial  arteries  are 
distributed  to  the  left  lung  and  one  to  the  right  lung.  The 
two  left  bronchial  arteries  spring  from  the  descending  aorta. 
The  right  bronchial  artery  is  a  branch  either  of  the  first  right 
aortic  intercostal  artery  or  of  the  upper  left  bronchial  artery. 
The  bronchial  arteries  and  their  branches  run  along  the 
posterior  surfaces  of  the  bronchi  and  their  branches,  and 
are  the  proper  nutrient  vessels  of  the  lungs.  Part  of  the 
blood  which  they  convey  to  the  lungs  is  returned  by  the  pul- 
monary veins  to  the  left  atrium  of  the  heart,  but  the  remainder 
is  returned  by  bronchial  veins,  which  open  on  the  right  side 
into  the  vena  azygos,  and  on  the  left  side  into  the  vena 
hemiazygos  accessoria,  or  into  the  left  superior  intercostal 
vein. 

Dissection. — After  the  bronchial  vessels  have  been  traced,  the  dissector 
should  separate  the  great  vessels  and  the  air  tube  from  each  other.  \Vhilst 
attempting  this,  he  will  find  that  his  work  is  greatly  impeded  by  the 
hardened  and  pigmented  bronchial  glands.  The  relative  positions  of  the 
constituent  parts  of  the  roots  of  the  lung  have  been  noted  already  (p.  22). 

The  Relations  of  the  Roots  of  the  Lungs. — Anterior  to  the 
root  of  each  lung  are  the  phrenic  nerve,  with  its  accompanying 
vessels,  and  the  anterior  pulmonary  plexus ;  behind  it,  the 
posterior  pulmonary  plexus,  and  below  it,  the  ligamentum 
pulmonis.      In  addition,  in  front  of  the  root  of  the  right  lung 


44 


THORAX 


is  the  superior  vena  cava,  and  above  and  behind  it,  the  vena 
azygos.  Whilst  above  the  root  of  the  left  lung  is  the  aortic 
arch,  and  behind  it,  the  descending  aorta  (Figs.  12  and  13). 
Bronchi. — There  are  two  primary  bronchial  tubes,  one 
for  each  lung.  They  spring  from  the  termination  of  the 
trachea,  and  each  passes  downwards  and  laterally,  in  the 
root  of  the  corresponding  lung,  to  the  hilus,  through  which 
it  enters  the  lung.  After  passing  through  the  hilus  it  descends, 
in  the  substance  of  the  lung,  to  the  base,  lying  nearer  the 
posterior  than  the  anterior  border.  In  the  root  of  the  lung 
the  bronchus  is  crossed  anteriorly  by  the  pulmonary  artery. 


First  thoracic 
verteb 


Fourth  thoracic 
vertebra 


Posterior 
mediastinum 


Superior 
mediastinum 
Manubrium  sterni 


Anterior 
mediastinum 


Middle  mediastinum 
Fig.  19. — Diagram  of  the  Mediastina. 

which  afterwards  descends  on  the  posterolateral  aspect  of  the 
intra-pulmonary  part  of  the  bronchial  tube. 

The  relations  of  the  bronchi  are  considered  later  (p.  96). 

The  Mediastinum  and  its  Contents. — It  has  been  pointed 
out  already  that  the  mediastinum  is  the  interval  which 
extends  from  the  sternum  to  the  vertebral  column  between 
the  two  pleural  sacs ;  that  it  is  occupied  by  some  of  the 
most  important  viscera,  vessels  and  nerves  in  the  body. 
I.e.  the  heart  enclosed  in  the  pericardium ;  the  aorta  and 
its  great  branches ;  the  great  vessels  which  carry  the  blood 
to  and  from  the  heart ;  the  oesophagus  and  trachea ;  the 
vagi    and   phrenic   nerves ;    and  the   thoracic   duct.     It   was 


THORACIC  CAVITY 


45 


noted  further  that  the  mediastinum  is  separated,  for  descrip- 
tive purposes,  into  two  main  parts,  the  superior  and  the 
inferior  mediastinum^  by  an  imaginary  plane  which  passes 
from  the  lower  border  of  the  manubrium   anteriorly  to  the 


Trachea 


Vertebral  artery 
Inferior  thyreoid  artery 
Transverse  cervical  artery 
Trunk  common  to  trans, 
cervical  and  trans,  scap.  arts.     ".I^SSTSTV 
Phrenic  nerve 

Right  common  carotid     - 


Right  innominate  vein 


Pericardiac  vein 

Internal  mammary  N;^^    w^^ 

vessels  •'"  vSyj' 

Cut  margins  of  right                  -'',^'mF'  \l  f 
pleura  and  of  j^      {ft 

pericardium jT  j       - 

Right  lung  .,..,...NfejMp^jB 

Right  coronary  /^F  ^'^ 

artery  /j  /|P 

Cut  margin  of     _^  ~~„„^-s^- 

right  pleura        -^         Mifcter        lU 

Cut  margin  of 
pericardium TlBwy '■tftti  **§£ 


Left  common  carotid 


Inferior  thj^reoid  artery 
-  Phrenic  nerve 

(  Trunk  of  trans,  cervical 
(  and  trans,  scap.  arteries 

Scalenus  anterior 

Left  innominate  vein 

Internal  mammary 
artery 


Left  lung 

Cut  margin  of 
left  pleura 

Ascending  aorta 


Cut  margin  of 
pericardium 

Right 
ventricle 


Fig.  20. — Dissection  of  the  Anterior  Part  of  the  Thorax.  The  sternum  and 
costal  cartilages  were  replaced  in  position  after  the  dissection  had  been 
made.  The  right  scalenus  anterior  is  cut  away  from  its  insertion  up  to 
the  level  of  the  upper  border  of  the  subclavian  arter)^ 

lower  border  of  the  fourth  thoracic  vertebra  posteriorly ;  it  has 
been  noted  also  that  the  inferior  mediastinum  is  separable 
into  three  parts:  (i)  the  a7iterior  mediastimwi^  anterior  to  the 
pericardium,  (2)  the  posterior  7?iediastinu?Ji,  posterior  to  the 
pericardium,  and  (3)  the  middle  7nediasti7iU7n  occupied  by  the 
pericardium,  the  heart,  the  great  vessels  immediately  adjacent 


46  THORAX 

to  the  heart,  and  the  phrenic  nerves  with  their  accompanying 
vessels.  These  sections  of  the  mediastinum  and  their  con- 
tents must  now  be  examined  in  detail. 

Dissection. — The  remains  of  the  anterior  part  of  the  mediastinal  pleura 
must  be  divided  longitudinally  immediately  posterior  to  the  sternum,  from 
the  lower  end  of  the  thorax  to  the  apices  of  the  pleural  sacs.  The  sternal 
extremities  of  the  first  ribs  must  be  then  cut  through,  close  to  the  manu- 
brium sterni,  and,  at  the  same  time,  the  sternal  heads  of  the  sterno-mastoid 
muscles  must  be  separated  from  the  manubrium,  if  that  has  not  already 
been  done  by  the  dissector  of  the  head  and  neck.  After  the  sterno- 
mastoid  muscles  and  the  first  ribs  are  divided,  the  sterno-hyoid  and  sterno- 
thyreoid  muscles  must  be  cut  through  transversely,  as  close  to  the  upper 
margin  of  the  manubrium  as  possible.  Next,  the  body  of  the  sternum  must 
be  separated  from  the  xiphoid  process  and  the  tips  of  the  seventh  costal 
cartilages.  The  sternum  vi^ith  the  attached  costal  cartilages  may  then  be 
removed  and  placed  aside,  but  it  must  be  carefully  preserved  for  future  use. 

When  the  sternum  is  removed  the  mediastinum  is  exposed  from  the 
front.  As  seen  from  the  front,  the  superior  mediastinum,  v^hich  lies  posterior 
to  the  manubrium,  is  a  relatively  vi^ide  triangular  area,  w^ith  its  apex  below^. 
The  anterior  mediastinum,  on  the  other  hand,  is  merely  a  narrow  cleft 
between  the  adjacent  anterior  margins  of  the  pleural  sacs,  except  opposite 
the  anterior  end  of  the  left  fifth  costal  cartilage  where  the  left  pleural  sac 
deviates  slightly  to  the  left  and  the  anterior  mediastinum  becomes  slightly 
wider  (Fig.  20). 

The  anterior  parts  of  both  the  superior  and  the  anterior  mediastina  are 
occupied  by  areolar  tissue  in  which,  as  far  down  as  the  third  or  fourth 
costal  cartilages,  remains  of  the  thymus  gland  may  be  found. 

Thymus. — The  thymus  gland  is  a  bilobed  organ,  developed 
from  the  third  visceral  clefts.  It  is  well  developed  in  the 
foetus  and  in  the  child  until  the  end  of  the  second  year. 
Then  it  frequently  undergoes  atrophy,  but  it  may  persist  even 
until  old  age. 

Dissection.  — All  the  remains  of  the  mediastinal  pleura  and  the  thymus  gland 
should  now  be  taken  away,  and  the  anterior  surface  of  the  pericardium  and 
the  contents  of  the  superior  mediastinum  should  be  thoroughly  cleaned. 
When  this  has  been  done  the  right  and  left  innominate  veins  and  their 
tributaries  will  be  exposed.  The  innominate  veins  should  be  traced  to 
their  union  with  the  superior  vena  cava.  To  the  left  of  the  superior  vena 
cava  and  below  the  left  innominate  vein  lie  the  upper  part  of  the  ascending 
portion  of  the  aorta,  and  the  anterior  part  of  the  aortic  arch.  When  these 
contents  of  the  upper  part  of  the  mediastinum  have  been  thoroughly  cleaned, 
the  various  structures  found  in  the  mediastinum  must  be  studied  in  detail. 

Vense  Anonymse. — The  innominate  vein  of  each  side  is 
formed  posterior  to  the  sternal  end  of  the  corresponding  clavicle 
by  the  union  of  the  internal  jugular  and  subclavian  veins 
of  the  same  side,  and  it  ends,  at  the  lower  border  of  the 
right  first  costal  cartilage,  by  uniting  with  its  fellow  of  the 
opposite  side  to  form  the  superior  vena  cava. 

The    right    innominate    vein    is    short    and    its    course    is 


THORACIC  CAVITY 


47 


almost  vertical.     It  is  accompanied  on  its  medial  side  by  the 
innominate  artery,  on  its  lateral  side  by  the  right  phrenic  nerve, 
and   posteriorly  by  the   right  vagus  nerve.      Antero-laterally 
it  is  in  relation  with  the  anterior  margin  of  the  right  pleura. 
The  left  i7ifiominate  vein  is  much  longer  than   the  right. 


Fig. 


Spinal  medulla 

Trachea 

CEsophagus 

4th  thoracic  vertebra 

Innominate  artery 

Left  common  carotid 
ft  innominate  vein 


^lanubrium  sterni 

Synchondrosis 

sternalis 

Right  pulmonary 
artery 

•Pericardial  cavity 

Left  atrium 
Aortic  valve 

Body  of  sternum 

Right  atrio- 
^•entricular  valve 

Wall  of  right 

^■entricle 

CEsophagus 

Diaphragm 
Descending  aorta 

Xiphoid  process 

•^  f    T- 
-m— ^--Liver 

21. — Sagittal  section  of  the  Thorax  of  an  old  man.  The  upper  border 
of  the  manubrium  sterni  and  the  bifurcation  of  the  trachea  are  lower 
than  in  the  averagje  adult. 


It  passes  obliquely  to  the  right  and  downwards,  posterior  to  the 
upper  half  of  the  manubrium  sterni ;  it  lies  posterior  to  the  re- 
mains of  the  thymus  gland  and  the  lower  ends  of  the  sterno-hyoid 
and  thyreoid  muscles,  and  anterior  to  the  three  great  branches 
of  the  aortic  arch  and  the  left  phrenic  and  vagus  nerves. 

Tributaries. — These  are  (i)  the  internal  jugular  vein,  (2) 
the  subclavian  vein,  (3)  the  vertebral  vein,  (4)  the  internal 
mammary  vein,  and  frequently  (5)  the  inferior  thyreoid  vein 


48 


THORAX 


of  the  same  side.  In  addition,  the  right  innominate  vein 
receives  the  right  lymph  duct,  or  lymph  vessels  from  the 
head  and  neck,  the  upper  extremity  and  the  right  half  of 
the  thorax  of  the  same  side ;  and  the  left  innominate  vein 
receives  (a)  the  left  superior  intercostal  vein,  (d)  some  peri- 
cardiac and  thymic  veins,  and  (c)  the  thoracic  duct. 

Dissection. — After  the  innominate  veins  and  their  tributaries  have  been 
studied  the  left  vein  may  be  pushed  aside,  or,  if  necessary,  it  may  be  cut 
in  order  to  display  the  three  great  branches  of  the  arch  of  the  aorta. 


artery 
Recurrent  nerve 


Left  innomi- 
nate vein 
Innominate 

artery  ^    . 

Phrenic  nerve  -f    ■'V 
Left  common 

carotid  artery  *♦    '  "     _.  v    ^ 

Vagus  nerve  -  f  ^^^  \       ^^^V\i 

Left  subclavian  ^,  ^  'V  ^^  J% 

Mediastinal  .  ''  j"^Lar- 

pleura  f  \    7"-* 

Thoracic  duct  ,       \ 


Cartilage  of 

,  i^      first  rib 

^\      Internal  mam- 
mary vessels 
Right  innomi- 
nate vein 
Phrenic  nerve 

Trachea 

Vagus 

CEsophagus 

Mediastinal 
pleura 


Fig.  22. — Transverse  section  through  the  Superior  Mediastinum 
at  level  of  the  third  thoracic  vertebra. 

Arteria  Anonyma. — The  innominate  artery  is  the  largest 
of  the  three  great  branches  of  the  aortic  arch.  It  com- 
mences, from  the  upper  border  of  the  arch,  posterior  to  the 
centre  of  the  manubrium,  passes  upwards  and  to  the  right, 
and  terminates,  posterior  to  the  upper  border  of  the  right  sterno- 
clavicular articulation,  by  dividing  into  the  right  common 
carotid  and  the  right  subclavian  arteries.  Anterior  to  it  are 
the  manubrium  sterni,  with  the  attachments  of  the  sterno- 
hyoid and  thyreoid  muscles,  the  right  sterno-clavicular  joint, 
the  remains  of  the  thymus  gland,  and  the  left  innominate  vein. 


THORACIC  CAVITY  49 

Posterior  to  its  lower  part  is  the  traciiea,  but  as  the  artery  passes 
upwards  and  to  the  right  it  gains  the  side  of  the  trachea  and 
has  the  upper  part  of  the  lung  and  pleura  posterior  to  it. 
To  its  left,  at  its  commencement,  is  the  left  common  carotid 
artery,  and  at  a  higher  level  the  trachea.  On  its  right  side 
is  the  right  innominate  vein,  which  separates  it  from  the  right 
phrenic  nerve  and  the  pleura.  As  a  rule  it  gives  off  its 
terminal  branches  only,  but  occasionally  a  small  artery,  called 
the  thyreoidea  i?na,  springs  from  it. 

The  Thyreoidea  Ima. — This  artery  is  frequently  absent.  \Yhen  it  is 
present  it  springs  from  the  innominate  artery,  or  from  the  arch  of  the  aorta, 
and  runs  upwards,  anterior  to  the  trachea,  to  the  thyreoid  gland. 

Arteria  Carotis  Communis  Sinistra. — The  left  common 
carotid  artery  springs  from  the  arch  of  the  aorta  immediately 
to  the  left  of,  and  slightly  posterior  to,  the  innominate  artery. 
It  passes  upwards,  through  the  superior  mediastinum  and 
posterior  to  the  left  sterno-clavicular  joint,  into  the  neck.  Its 
anterior  relations  in  the  thorax  are  similar  to  those  of  the 
innominate  artery.  Posterior  to  it,  from  below  upwards,  are  the 
trachea,  the  left  recurrent  nerve,  the  oesophagus  and  the 
thoracic  duct,  and,  on  a  plane  somewhat  more  to  the  left,  the 
left  phrenic  and  vagus  nerves,  and  the  subclavian  artery.  To 
its  right  lie  first  the  innominate  artery,  and  then  the  trachea ; 
and  to  its  left  is  the  left  pleura.  It  gives  off  no  branches  in 
the  thorax. 

Arteria  Subclavia  Sinistra. — The  left  subclavian  artery 
springs  from  the  posterior  part  of  the  aortic  arch,  posterior  to 
the  left  common  carotid.  It  passes  vertically  upwards,  through 
the  superior  mediastinum  and  posterior  to  the  sternal  end  of 
the  clavicle,  into  the  root  of  the  neck.  Anterior  to  it  are  the 
left  phrenic  and  vagus  nerves,  which  separate  it  from  the 
left  common  carotid  artery.  Posterior,  and  to  its  left  side,  it 
is  in  relation  with  the  left  mediastinal  pleura  and  the  lung. 
To  its  right  side  are  the  trachea  and  the  left  recurrent 
nerve,  and,  at  a  higher  level,  the  oesophagus  and  the 
thoracic  duct.  It  gives  off  no  branches  in  the  thoracic  part 
of  its  course. 

Dissection. — The  lateral  walls  of  the  pericardium  have  already  been 
exposed  and  opened  (see  p.  33)  ;  the  flaps  then  made  should  be  replaced 
and  fixed  in  position.  When  this  has  been  done,  the  outline  of  the  sac 
will  be  fully  displayed,  and  the  dissectors  can  then  study  its  relations  to 
adjacent  organs. 

VOL.  II — 4 


50  THORAX 

The  Pericardium. — This  is  a  fibro-seioiis  sac  which  occupies 
the  middle  mediastinum.  It  surrounds  the  heart  and  the  roots 
of  the  great  vessels  which  enter  and  leave  the  heart. 

llic  Fibrous  Faicardiiim, — The  fibrous  or  outer  part  of 
the  pericardium  is  conical  in  form.  Its  base  rests  upon  the 
diaphragm,  principally  on  the  central  tendon  but  also 
upon  the  muscular  ]H:>rtion,  particularly  upon  the  left  side. 
Near  the  median  plane  it  is  blended  with  the  central  tendon, 
and  can  be  separated  from  it  only  by  the  aid  of  the  edge 
of  the  scalpel ;  more  laterally  the  areolar  tissue  which 
connects  the  pericardium  and  the  diaphragm  is  easily  broken 
down  by  the  handle  of  the  knife.  The  diaphragm  separates 
the  pericardium  mainly  from  the  upper  surface  of  the  liver,  but 
also,  towards  the  left  and  anteriorly,  from  the  fundus  of  the 
stomach,  llie  apex  of  the  fibrous  sac  blends  with  the  outer 
coats  of  the  aorta,  the  pulmonary  arteries  and  the  superior 
vena  cava.  The  anterior  surface  lies  behind  the  body  of  the 
sternum  and  the  cartilages  of  the  ribs  from  the  second  to  the 
sixth  inclusive,  but  it  is  separated  from  them  by  the  lungs  and 
pleurae,  except  (i)  in  the  median  plane  of  the  anterior  medi- 
astinum, where  condensations  of  the  areolar  tissue  of  the  medi- 
astinum, called  the  superior  and  inferior  sterno-pe7'icardiac 
li^amcnts^  connect  the  anterior  surface  of  the  fibrous  sac  to 
the  upper  and  lower  ends  of  the  body  of  the  sternum 
respectively,  and  (2)  in  the  region  of  the  sternal  extremity  of 
the  left  fifth  costal  cartilage,  where  the  left  pleura  retreats 
somewhat  towards  the  left  side,  and  the  pericardium  comes 
into  direct  relation  with  the  sternum  and  the  left  transversus 
thoracis  muscle.  This  portion  of  the  pericardium  is  the 
so-called  bare  area.  It  is  usually  of  small  extent,  and  iVeciuently 
it  does  not  extend  beyond  the  margin  of  the  sternum,  but  it  is 
of  importance  because  through  it  the  surgeon  attempts  to  tap 
the  pericardium  when  the  sac  is  distended  with  fluid. 

The  lateral  ivalls  of  the  pericardium  are  in  relation  with 
the  mediastinal  pleura,  the  phrenic  nerve  and  the  pericardiaco- 
phrenic vessels  intervening  (O.T.  comes  nervi  phrenici).  The 
posterior  surface  lies  anterior  to  the  descending  aorta  and  the 
cxjsophagus  medially,  whilst  laterally  it  is  supported  posteriorly 
by  the  lungs  and  pleunxi.  At  the  junction  of  the  upper  parts  of 
the  lateral  and  posterior  surfaces,  on  each  side,  two  pulmonary 
veins  enter  the  pericardium  and  receive  sheaths  from  its 
fibrous  wall. 


THORACIC  CAVITY 


5» 


Diner t ion. — When  the  relations  and  prolongations  of  the  fibrous  peri- 
cardium have  been  studied,  the  two  anterior  flaps  already  made  in  the 
lateral  walls  of  the  sac  (see  p.  33)  should  \yt  connected  together  and  c<'>n- 
verted  into  one  large  anterior  flap.  This  can  be  done  by  a  transverse  cMi^ 
passing  across  the  median  plane  just  above  the  diaphragm.  The  large 
triangular  flap  thus  formed  should  be  thrown  upwards  towards  the  apex  of 
the  pericardium. 


Left  common  carotid  artery 
Left  vagus  nerve— 

I>eft  subclavian  artery 
Left  innominate  vein 


Trachea 


Left  pulmonary 
artery 

I^eft  bronchu'S 


Left  pulmonary 
veins 


Right  vagus  ner 


Diaphragmatic 
surface  of  heart 


Innominate  artery 
_CRiV>phagus 

_ Right  vagoA  nerve 

Superior  vena  cava 


Vena  azygos 

Right  posterior 
pulmonary  plexus 
Right  pulmonary 
artery 

Right  bronchus 


Right  pulmonary 
veins 

("Esophageal  plexus 


Portion  of  peri- 
cardium 


I/cft  vagus  nerve 


Inferior  vena  cava 


Fig.  23. — Posterior  Aspect  of  the  Heart  with  the  Descending  Aorta,  the 
Trachea  and  Bronchi,  and  the  QEsophagus. 


The  Serous  Pericardium.  —  The  serous  pericardium  is  a 
closed  and  invaginated  sac  which  lines  the  inner  surface  of 
the  fibrous  sac  and  envelops  the  heart  and  the  roots  of  the 
great  vessels  passing  to  and  from  the  heart. 

The  uninvaginated  portion  of  the  wall  of  the  serous  sac, 


52 


THORAX 


which  Hnes  the  inner  surface  of  the  fibrous  sac,  is  called  the 
parietal  layer,  and  the  invaginated  portion,  which  envelops  the 
heart,  is  the  visceral  portion.  The  inner  surface  of  the  sac  is 
fined  by  a  flat  endothefium,  and,  during  health,  is  smooth  and 

Inferior  thyreoid  veins 
Right  common  carotid  artery         / ',        Left  common  carotid  artery 


Right  internal  jugular  vein  --j-» 
Right  subclavian  artery  — *H 
Right  subclavian  vein   --^^* 


Left  internal  mammarj'  vein ' 

Right  internal  mammary. 

vein 

Cut  edge  of  filarous 

pericardium 

Superior  vena  cava.. 

Cut  edge  of  serous  Ji_ 
pericardium 
Aorta 

Division  of  pul- 
monary' arterj' 
Right  pulmonary  artery 
Superior  vena  cava 
Upper  right 
pulmonary  vein 


Lower  right  pu 
monary  vein 

Cut  edges  of 
serous  pericardium 

Inferior  vena  cava 


Left  internal  jugular  vein 
Thoracic  duct 
'limm  Left  subclavian  artery 
Left  subclavian  vein 

-  Left  phrenic  nerve 

-Left  vagus 
Left  superior  intercostal  vein 


Left  recurrent  nerve 

Ligamentum  arteriosum 

Left  pulmonary  artery 
Arrow  in  transverse  sinus 
Left  bronchus 
Upper  left  pulmonary  vein 

Lower  left  pulmonary  vein 


Fibrous  pericardium 
Serous  pericardium 


Fig.  24. — The  Pericardium  and  Great  Vessels  of  the  Heart.  The  thoracic 
organs  were  hardened  in  situ  by  formalin  injection.  The  pericardium 
having  been  opened  by  the  removal  of  its  anterior  wall,  the  great  vessels 
were  divided  and  the  heart  removed. 


gfistening.  The  parietal  and  visceral  layers  are  separated, 
during  health,  merely  by  a  thin  layer  of  serous  fluid,  which 
prevents  friction  between  the  two  surfaces  as  they  move  over 
each  other  during  the  contractions  and  expansions  of  the 
heart. 


THORACIC  CAVITY  53 

The  Sterno- costal  Surface  of  the  Heart. — Before  the 
dissectors  disturb  the  heart,  which  has  been  exposed  by  the 
reflection  of  the  anterior  wall  of  the  pericardium,  they  should 
note  carefully  not  only  the  parts  of  the  heart  which  are  visible, 
but  also  their  relations  to  the  anterior  wall  of  the  thorax. 
The  latter  they  can  easily  do  by  replacing  the  sternum  and 
costal  cartilages  in  position  from  time  to  time. 

They  will  find  that  the  sterno-costal  surface  is  divided 
into  an  upper,  right,  or  atrial  portion  and  a  lower,  left,  or 
ventricular  portion  by  an  oblique  sulcus,  the  corojiary  sulcus 
(O.T.  auriculo-ventricular),  which  is  quite  distinct  below  and 
on  the  right,  but  is  masked  above  and  to  the  left  by  the 
roots  of  the  pulmonary  artery  and  the  aorta.  The  position 
of  this  sulcus  can  be  indicated  on  the  surface  by  a  line 
extending  obliquely  downwards  and  to  the  right,  from  the 
sternal  end  of  the  third  left  to  the  sternal  end  of  the  sixth 
right  costal  cartilage.  Below  and  to  the  left  of  the  sulcus 
is  the  ventricular  part  of  the  sterno-costal  surface,  termi- 
nating on  the  left  and  below  in  the  apex  of  the  heart,  which 
lies  posterior  to  the  fifth  left  intercostal  space,  three  and  a  half 
inches  from  the  median  plane.  The  ventricular  area  of  the 
sterno-costal  surface  is  divided  by  the  anterior  longitudinal 
sulcus  (O.T.  anterior  interventricular  sulcus)  into  a  right 
two-thirds,  formed  by  the  right  ventricle,  and  a  left  third, 
formed  by  the  left  ventricle.  The  anterior  longitudinal 
sulcus  terminates  on  the  lowxr  border  of  the  sterno-costal 
surface,  to  the  right  of  the  apex,  in  a  slight  notch,  the  mcisura 
cordis.  The  apex,  therefore,  is  formed  entirely  by  the  left 
ventricle.  The  lower  margin  of  the  sterno-costal  surface  lies 
on  the  diaphragm.  It  is  formed  chiefly  by  the  lower  border 
of  the  right  ventricle,  and  only  to  a  small  extent  by  the  apical 
part  of  the  left  ventricle. 

The  upper  and  right  portion  of  the  sterno-costal  surface  is 
formed  by  the  atria,  which  are  to  a  large  extent  concealed  by 
the  pulmonary  artery  and  the  ascending  part  of  the  aorta. 
Above  and  to  the  right  is  the  right  atrium,  continuous  above 
with  the  superior  vena  cava  and  below  with  the  inferior  vena 
cava,  whilst  its  auricular  portion  (O.T.  auricular  appendage) 
curves  upwards  and  to  the  left,  along  the  line  of  the  coronary 
sulcus,  to  the  root  of  the  pulmonary  artery. 

Crossing  the  front  of  the  right  atrium,  immediately  below 
the  lower  end  of  the  superior  vena  cava,  is  a  sulcus,  the  sulcus 


54 


THORAX 


terjninalis.  If  the  heart  is  pulled  a  little  over  to  the  left  this 
sulcus  can  be  traced  downwards,  along  the  lateral  aspect  of 
the  right  atrium,  to  the  anterior  aspect  of  the  upper  end  of 
the  inferior  vena  cava.      It  indicates  the  separation  between 


Right  common  carotid  artery 
Opening  of  right  internal  jugular  vein 
■>  Right  subclavian  artery- 
Right  subclavian  vein 

A 


Innominate  artery 


Superior  vena  cava 
Right  phrenic  nerve 

Eparterlal  branch  of 
right  bronchus 

iPulmonary  artery 

Upper  right  pulmonary' 

vein 

Right  auricle 

(O.T.  appendix) 


Left  common  carotid  artery 

End  of  left  internal  jugular  vein 
Left  subclavian  artery 
Left  subclavian  vein 


Infer 


Right  atrium 


lor  vena  cava 


// 


/' 


Left  phrenic  nerve 
Cut  edge  of  peri- 
cardium 
Ascending  aorta  , 

Root  of  pulmonary 
artery 


y.'/ 


Coronary  sulcus 
(O.T.  auriculo- 
ventricular) 

Right  ventricle 

Anterior  longi- 
tudinal sulcus 
Left  ventricle' 


Cut  edge  of 


pericar- 
dium 


Fig.  25.— Dissection  of  the  Middle  and  Superior  Parts  01  tlie  Mediastinum 
from  the  anterior  aspect. 

the  venous  sinus  of  the  atrium,  into  which  the  great  veins 
open,  and  the  cavity  of  the  atrium  proper. 

The  whole  of  the  right  border  of  the  heart  is  formed  by 
the  right  atrium.  Its  position  can  be  indicated  on  the  surface 
by  a  Hne,  convex  to  the  right,  which  commences  at  the  level 
of  the   third   right   costal   cartilage,    half  an    inch   from   the 


THORACIC  CAVITY  55 

sternum,  and  terminates  opposite  the  sixth  right  cartilage  at 
the  same  distance  from  the  right  margin  of  the  sternum.  At 
the  upper  and  left  corner  of  the  atrial  area  is  the  apex  of  the 
left  auricle  (O.T.  auricular  appendage),  and  between  the  two 
auricles  are  the  roots  of  the  pulmonary  artery  and  the  aorta, 
the  former  anterior  to  the  latter.  The  rounded  portion  of 
the  upper  part  of  the  right  ventricle,  immediately  below  the 
pulmonary  artery,  is  the  co}ms  arteriosus. 

If  a  finger  is  introduced  into  the  cleft  betw^een  the  aorta 
anteriorly  and  the  superior  vena  cava  posteriorly,  it  can  be 
passed  across,  from  the  right  to  the  left  side  of  the  pericardial 
cavity,  through  a  passage,  called  the  transverse  sinus  of  the 
pericardium  (Figs.  24  and  27).  This  sinus  lies  anterior  to  the 
superior  vena  cava  and  the  atria,  and  posterior  to  the  ascending 
aorta  and  the  stem  of  the  pulmonary  artery.  The  upper  border 
of  a  finger  placed  in  the  sinus  will  indicate  the  position  of  the 
upper  border  of  the  heart.  This  border  is  formed  to  a  slight 
extent  by  the  upper  border  of  the  right  atrium,  but  mainly  by 
the  upper  border  of  the  left  atrium.  Its  position  can  be  in- 
dicated, on  the  anterior  surface  of  the  body,  by  a  line  com- 
mencing half  an  inch  from  the  side  of  the  sternum  at  the  lower 
border  of  the  second  left  costal  cartilage,  and  ending  at  the 
same  distance  from  the  sternum  on  the  upper  border  of  the 
third  right  cartilage.  Whilst  a  finger  is  kept  in  the  transverse 
sinus  a  pointer  should  be  introduced  into  the  right  pulmonary 
artery  through  its  cut  end  in  the  root  of  the  right  lung.  The 
dissector  will  note,  as  the  pointer  traverses  the  right  pulmonary 
artery,  that  it  passes  first  posterior  to  the  superior  vena  cava  and 
then  along  the  upper  border  of  the  transverse  sinus,  that  is 
along  the  upper  border  of  the  heart  where  that  border  is 
formed  by  the  left  atrium ;  therefore  the  position  of  the  right 
pulmonary  artery  may  be  indicated,  on  the  anterior  surface 
of  the  body,  by  the  right  two-thirds  of  the  line  which  marks 
the  position  of  the  upper  border  of  the  heart. 

The  left  border  of  the  anterior  surface  of  the  heart  is 
formed,  to  a  slight  extent,  by  the  left  atrium,  but  mainly  by 
the  left  ventricle.  It  is  convex  to  the  left  and  its  position 
is  marked,  on  the  surface  of  the  body,  by  a  line  which  com- 
mences above  at  the  lower  border  of  the  left  second  costal 
cartilage,  half  an  inch  from  the  sternum,  and  terminates  below 
at  the  apical  point  in  the  fifth  left  intercostal  space. 

Before  proceeding  further  the  dissector  should  summarise 


56 


THORAX 


the  information  he  has  gained  regarding  the  relationship  of 
the  apex  of  the  heart  and  the  borders  of  the  sterno-costal 
surface  of  the  heart  to  the  anterior  wall  of  the  thorax.  The 
upper  border  is  formed  by  the  atria,  and  as  the  heart  lies  in 
situ  it  is  concealed  to  a  great  extent  by  the  aorta  and  the 


Fig.  26. — The  relations  of  the  Heart  and  of  its  Orifices  to  the  Anterior 
Thoracic  Wall.      (Young  and  Robinson.) 


I  to  VII.   Costal  cartilages. 
A.  Aorta. 
Ao.  Aortic  orifice. 

C.  Clavicle. 
LA.   Left  atrium. 
LV.  Left  ventricle. 


M.  Mitral  orifice. 

P.   Pulmonary  orifice. 
RA.  Right  atrium. 
RV.  Right  ventricle. 
SVc.  Superior  vena  cava. 

T.   Tricuspid  orifice. 


pulmonary  artery.  Its  position  is  marked  on  the  surface 
by  a  line  extending  from  the  lower  border  of  the  second 
left  to  the  upper  border  of  the  third  right  costal  cartilage, 
commencing  and  terminating  about  half  an  inch  from  the 
border  of  the  sternum.  The  right  border  is  formed  entirely 
by  the  right  atrium,  and  its  position  is  indicated  on  the  sur- 


THORACIC  CAVITY  57 

face  by  a  line,  convex  to  the  right,  commencing  above  at  the 
lower  border  of  the  right  second  costal  cartilage,  half  an  inch 
from  the  side  of  the  sternum,  and  terminating  below  at  the 
sixth  right  cartilage  half  an  inch  from  its  junction  with  the 
sternum.  More  than  two-thirds  of  the  lower  border  are  formed 
by  the  right  ventricle,  and  the  remainder  by  the  apical  portion 
of  the  left  ventricle,  and  the  two  parts  may  be  separated  by 
a  distinct  notch,  the  incisura  cordis.  This  border  is  slighdy 
concave  downwards,  in  correspondence  with  the  upward 
convexity  of  the  diaphragm  on  which  it  rests,  and  it  has  a 
slight  inclination  downwards  and  to  the  left.  It  is  marked, 
on  the  surface  of  the  body,  by  a  line  extending  from  the 
sixth  right  costal  cartilage,  near  the  sternum,  to  the  apical 
point,  which  lies  in  the  left  fifth  intercostal  space  from  3 J 
to  3  J  inches  from  the  median  plane.  The  left  border,  which 
is  formed  mainly  by  the  left  ventricle  and  only  to  a  slight 
extent  by  the  left  atrium,  extends  from  the  apex  to  a  point 
on  the  lower  border  of  the  left  second  costal  cartilage  half 
an  inch  from  the  margin  of  the  sternum. 

The  coronary  sulcus,  which  indicates  the  plane  of  union 
of  the  atria  and  ventricles  and,   therefore,  the  plane  of  the 
atrio -ventricular  and   aortic   and    pulmonary  orifices  of   the 
heart,  can  be  indicated,  on  the  surface,  by  a  line  extending 
from  the  sternal  end  of  the  third  left  costal  cartilage  to  the 
sternal  end  of  the  sixth  right  cartilage.     Posterior  to  the  left 
extremity  of  this  line,  at  the  level  of  the  upper  part  of  the 
third  left  costal  cartilage,  is  the  orifice  of  the  pulmonary  artery. 
The  aortic  orifice  is  a  litde  low^er  and  slightly  to  the  right, 
posterior  to  the  sternum  at  the  level  of  the  low^er  border  of  the 
third   left   cartilage.     Immediately  below   the   aortic   orifice, 
posterior  to  the  left  margin  of  the  sternum,  at  the  level  of  the 
upper  part  of  the  fourth  left  cartilage,  lies  the  mitral  orifice ; 
and  the  tricuspid  orifice  is  situated  posterior  to  the  middle  of 
the  sternum,    opposite   the   fourth   intercostal    spaces.     The 
positions  of  the  great  orifices  cannot  be  confirmed  at  this 
stage  of  the  dissection,  and  they  will  be  noted  again  at  a 
later  period  when  the  heart  is  opened. 

After  the  sterno-costal  aspect  of  the  heart,  the  boundaries 
of  the  transverse  sinus,  and  the  general  position  of  the  heart 
have  been  studied,  the  dissectors  should  turn  the  apex  of  the 
heart  upwards  and  to  the  right,  and  examine  the  inferior 
and  posterior  surfaces  whilst  the  heart  is  still  in  situ.     They 


58 


THORAX 


will  find  that  the  inferior  or  diaphragmatic  surface^  which 
rests  upon  the  diaphragm,  is  slightly  concave;  that  it  is 
formed  entirely  by  the  ventricles,  and  mainly  by  the  left 
ventricle,  which  forms  the  left  two -thirds,  the  separation 
between  the  ventricles  being  indicated  by  the  inferior  longi- 
tudinal sulcus.  As  the  apex  of  the  heart  is  held  upwards 
and  to  the  right,  the  dissector  should  note  that  a  recess  of 


Innominate  artery 


Aortic  arch  — 
Pulmonary  artery  ._ 


Pulmonary  valve 
Conus  arteriosus 

Pericardial  cavity 
Ascending  aorta 


Aortic  valve  .. 
Aortic  sinus  ., 


Left  common  carotid 


Superior  vena  cava 


Vena  azygos 

Right 
— pulmonary  artery 

>  Right  pulmonary 

artery 
Transverse  sinus 
eft  pencaraium  " 
Qbliq^ue  sinus 
of  pericar3Tum 
Upper  right 
pulmonary  vein 
Left  atrium 


Lower  left 
pulmonary  vein 


Base  of  anterior  cusp 
of  mitral  valve 
Oblique  sinus  of  pericardium 

Coronary  sinus 


Fig.  27. — Sagittal  Section  of  Heart. 

the  pericardial  cavity  ascends  posterior  to  the  base  or  posterior 
surface  of  the  heart.  This  recess  is  the  oblique  sinus  of  the 
pericardium.  Its  orifice  is  below,  where  it  is  bounded  to 
the  right  and  below  by  the  upper  end  of  the  inferior  vena 
cava,  and  to  the  left  and  above  by  the  left  inferior  pulmonary 
vein.  The  posterior  boundary  of  the  sinus  is  the  pericardium; 
and  the  pericardium  separates  the  cavity  of  the  sinus  from 
the  oesophagus,  which,  at  this  level,  is  lying  between  the 
pericardium  and  the  descending  part  of  the  thoracic  portion 
of  the  aorta.     Both   the  oesophagus  and   the  aorta  can  be 


THORACIC  CAVITY  59 

palpated  through  the  posterior  wall  of  the  sinus.  The 
anterior  wall  of  the  oblique  sinus  is  the  posterior  wall  of 
the  left  atrium  (Fig.  27).  If  the  dissector  passes  his  left 
index  finger  into  the  transverse  sinus  and  the  middle  and 
index  fingers  of  his  right  hand  into  the  oblique  sinus,  he  will 
be  able  to  convince  himself  that  the  left  atrium  is  the  only 
structure  which  intervenes  between  the  cavities  of  the  two 
sinuses.  When  he  has  satisfied  himself  regarding  this  point, 
he  should  note  that  the  lower  and  posterior  part  of  the 
coronary  sulcus  of  the  heart  extends  across  the  lower  part 
of  the  base  between  the  posterior  end  of  the  left  ventricle 
and  the  lower  end  of  the  left  atrium,  and  that  it  is  occupied 
by  the  coronary  blood  sinus,  which  opens  into  the  right 
atrium  immediately  to  the  left  of  the  upper  end  of  the  in- 
ferior vena  cava. 

A  complete  examination  of  the  base  of  the  heart  cannot 
be  made  until  the  heart  is  removed  from  the  thorax  at  a  later 
stage  of  the  dissection,  and  the  dissectors  should  pass  now 
to  a  consideration  of  the  relation  of  the  serous  layer  of  the 
pericardium  to  the  great  vessels  which  are  entering  or  leaving 
the  heart  (see  Fig.  24).  They  have  previously  noted  (p.  51) 
that  the  visceral  layer  of  the  serous  portion  of  the  pericardium 
covers  almost  every  portion  of  the  heart,  the  only  part  left 
uncovered  being  the  upper  border  of  the  left  auricle,  which 
is  in  contact  wdth  the  lower  border  of  the  right  pulmonary 
artery.  Along  this  border  the  visceral  part  of  the  serous  layer 
of  the  pericardium,  ascending  on  the  anterior  aspect  of  the 
left  atrium,  becomes  continuous  with  the  parietal  layer  which 
passes  anteriorly,  in  the  roof  of  the  transverse  sinus,  on  the 
lower  wall  of  the  right  pulmonary  artery,  to  the  posterior 
surface  of  the  ascending  part  of  the  aorta,  where  it  becomes 
continuous  with  the  visceral  layer  which  descends  on  the 
posterior  surface  of  the  aorta,  in  the  anterior  wall  of  the 
transverse  sinus.  Along  the  same  border  the  visceral  part 
of  the  serous  pericardium  is  reflected  posteriorly  in  the  roof 
of  the  oblique  sinus,  to  become  continuous  with  the  parietal 
layer  on  the  posterior  wall  of  the  pericardial  sac.  The 
fact  that  he  can  pass  his  finger  through  the  transverse  sinus 
posterior  to  the  aorta  and  the  pulmonary  artery,  but  cannot 
insinuate  it  between  the  two  vessels,  will  indicate  to  the 
student  that  the  two  great  arteries  are  enclosed  in  a  tubular 
sheath   of  the   visceral   part   of  the  serous  membrane.     An 


6o  THORAX 

examination  of  the  venae  cavse  will  show  that  the  lower  inch 
of  the  superior  vena  cava  lies  within  the  fibrous  pericardium 
and  that  it  is  ensheathed,  except  along  its  postero-medial 
border,  by  a  covering  of  the  serous  layer,  whilst  the  inferior 
vena  cava  can  scarcely  be  said  to  have  any  intra-pericardial 
course,  for  it  joins  the  lower  and  posterior  part  of  the  right 
atrium  immediately  after  piercing  the  fibrous  layer,  but  the 
margin  of  the  orifice  by  which  it  enters  is  surrounded  by  the 
serous  layer  except  along  a  narrow  line  posteriorly.  The 
left  pulmonary  veins  are  covered  by  the  serous  layer  on  their 
superior,  anterior,  and  inferior  aspects,  but  not  posteriorly ; 
and  the  right  pulmonary  veins,  which  enter  the  left  auricle  as 
soon  as  they  have  pierced  the  fibrous  pericardium,  are  in  rela- 
tion with  the  serous  layer  merely  along  the  medial  and  lateral 
borders  of  the  orifices  in  the  fibrous  layer  through  which 
they  enter. 

Dissection. — After  the  examination  of  the  reflections  of  the  serous  layer 
of  the  pericardium  is  completed,  the  dissectors  should  study  the  vessels  and 
nerves  which  supply  the  walls  of  the  heart.  They  are  the  coronary  arteries 
and  the  cardiac  veins  and  nerves,  and  they  lie  in  the  coronary  and  longitudinal 
sulci  of  the  heart,  which  have  been  noted  already.  To  display  them  the 
visceral  pericardium  superficial  to  them  must  be  cut  and  turned  aside,  the  fat 
which  lies  in  the  sulci  around  the  vessels  must  be  removed,  then  the  main 
vessels  can  be  traced  to  their  origins  and  terminations,  and  an  endeavour 
should  be  made  to  preserve  the  fine  nerves  which  accompany  the  vessels. 

Arterise  Coronarise. — The  coronary  arteries  are  the  nutrient 
vessels  of  the  heart.  They  spring  from  dilatations  of  the  com- 
mencement of  the  aorta  which  are  called  the  sinus  aortce. 
(Valsalva).  There  are  three  sinuses  of  the  aorta,  an  anterior 
and  two  posterior,  and  only  two  coronary  arteries,  a  right  and 
a  left ;  the  right  artery  springs  from  the  anterior  sinus,  and 
the  left  from,  the  left  posterior  sinus. 

The  right  coronary  artery  passes  anteriorly  from  the  anterior 
aortic  sinus,  between  the  pulmonary  artery  and  the  right 
auricle  ;  turns  downwards  and  to  the  right,  in  the  coronary 
sulcus,  to  the  lower  part  of  the  right  margin  of  the  heart,  round 
which  it  curves.  Then  it  proceeds  to  the  left,  in  the  posterior 
part  of  the  coronary  sulcus,  till  it  reaches  the  posterior  end 
of  the  inferior  (posterior)  longitudinal  sulcus,  where  it  divides 
into  a  small  transverse  and  a  large  interventricular  branch. 
The  transverse  branch  continues  to  the  left  till  it  anastomoses 
with  the  circumflex  branch  of  the  left  coronary  artery.  The 
interventricular   (descending)    branch    runs    anteriorly   in    the 


THORACIC  CAVITY 


6i 


inferior  longitudinal  sulcus  on  the  diaphragmatic  surface  of 
the  heart,  and  it  anastomoses  with  the  interventricular  or 
descending  branch  of  the  left  coronary  artery  at  the  cardiac 
notch  on  the  lower  margin  of  the  heart.  In  addition  to  its 
terminal  branches,  the  right  coronary  artery  supplies  branches 
to  the  roots  of  the  pulmonary  artery  and  the  aorta,  and  to 


Left 

pulmonary 

artery 


Pulmonary  artery 

Interventricular 

branch  of  left 

coronary  artery 

Left  posterior  sinus 

of  aorta 

Circumflex 

branch  of  left 

coronary  artery 

Anterior  cusp  of 
mitral  valve 

Posterior  cusp 


Ligamentum  arteriosum 

Pulmonary  artery 
-Aorta 


Right  pulmonary'  artery 


Conus  arteriosus 


Right  coronary  artery 

jl^      Right  posterior  sinus 
of  aorta 


Anterior  cusp 
of  tricuspid  valve 


Inferior  cusp 
Medial  cusp 


Marginal  branch 
Interventricular  branch  of  right  coronary  artery 

Fig.  28. — The  Base  of  the  Ventricular  Part  of  the  Heart  from  which  the 
Atria  have  been  removed.  The  detached  atria  are  depicted  in  Fig. 
31,      The  specimen  was  hardened  in  situ. 

the  walls  of  the  right  atrium  and  the  right  ventricle,  the 
larger  and  more  numerous  branches  being  given  to  the 
ventricle.  One  of  the  latter,  the  marginal  branch,  passes 
along  the  lower  margin  of  the  heart  towards  the  apex  ot  the 
ventricle  (see  Fig.  29). 

The  left  corona?y  artery,  as  it  springs  from  the  left 
posterior  aortic  sinus  (Fig.  28),  lies  posterior  to  the  pulmonary 
artery.  For  a  short  distance  it  runs  to  the  left,  then  it  turns 
anteriorly,  between  the  pulmonary  artery  and  the  left  auricle. 


62 


THORAX 


and  divides  into  a  descending  or  interventricular,  and  a 
circumflex  branch.  The  interventricular  branch  passes  down 
the  sterno-costal  surface  of  the  heart,  in  the  anterior  longitudinal 
sulcus  (Fig.  29),  and  turning  round  the  lower  border,  in  the 
cardiac  notch,  it  anastomoses  with  the  interventricular  branch 


Right 

innominate  vein 
Innominate  artery 


Superior  vena  ca^•c 


Serous 
pericardium 


Apex  of  right  auricle 
(O.T.  appendix) 


Coronar> 


Marginal  branch 

of  right  coronary 

artery 


Right  ventricle- 


Left  common  carotid 
Left  subclavian 

Left  innominate  vein 

Aortic  arch 
Ligamentum  arteriosum 

Left  pulmonary  artery 
Pulmonary  artery 

Left  auricle  (O.T.  appendix) 
Conus  arteriosus 


Anterior  interven- 
tricular furrow  with 
the  interventricular 
branch  of  the  left  coro- 
nary artery  and  the 
great  cardiac  vein 

Left  ventricle 


Apex  of  heart 


Fig.  29. — Sterno-costal  Surface  of  the  Heart. 


of  the  right  coronary  artery.  The  circumflex  bra?ich  runs  to 
the  left,  in  the  coronary  sulcus,  turns  round  the  left  border 
of  the  heart  (Fig.  28)  and  anastomoses,  on  the  posterior 
surface,  with  the  transverse  terminal  branch  of  the  right 
coronary.  From  the  stem  of  the  artery  twigs  are  given  to 
the  roots  of  the  pulmonary  artery  and  the  aorta,  and  its 
terminal  branches  supply  the  walls  of  both  ventricles  and  the 
walls  of  the  left  atrium. 

Venae  Cordis. — The  cardiac  veins  are:   (i)  the  coronary 


THORACIC  CAVITY 


63 


sinus;  (2)  the  great  cardiac  vein;  (3)  the  inferior  (posterior) 
ventricular  vein  ;  (4)  the  middle  cardiac  vein  ;  (5)  the  oblique 
vein;  (6)  the  small  cardiac  vein;  (7)  the  anterior  cardiac 
veins ;  and  (8)  the  venae  minimae  cordis. 

The  coronary  si?tus  lies  at  the  base  of  the  heart,  in  the 
posterior  part  of  the  coronary  sulcus,  between  the  left  atrium 
and  the  left  ventricle.  It  can  be  displayed  when  the  apex  of 
the  heart  is  turned  upwards  and  to  the  right.  Its  right 
extremity  opens  into  the  right  atrium,  immediately  below  and 
to  the  left  of  the  orifice  of  the  inferior  vena  cava.     At  its  left 


Oblique  vein 


Coronarj'  sinus 


^■^     Great  cardiac  vein 

I 


Small  cardiac 


Middle  cardiac 
vein 


Inferior  ventricular  \ein 


Great  cardiac 

vein 


Fig.  30. — The  Coronarj^  System  of  Veins  on  the  Surface  of  the 
Heart.      (Diagram. ) 

extremity  it  receives  the  great  cardiac  vein.  The  great  cardiac 
vein  ascends  along  the  anterior  longitudinal  sulcus  (Fig.  29), 
where  it  lies  in  relation  with  the  interventricular  branch  of  the 
left  coronary  artery.  At  the  upper  end  of  the  interventricular 
sulcus  it  turns  round  the  left  border  of  the  heart,  with  the 
circumflex  branch  of  the  left  coronary  artery,  and  it  ends  in 
the  left  extremity  of  the  coronary  sinus.  The  inferior 
(posterior)  ventricular  veiti  or  veins,  from  the  diaphragmatic 
surface  of  the  left  ventricle,  and  the  middle  cardiac  vein,  which 
runs  posteriorly  in  the  inferior  longitudinal  sulcus,  end  in  the 
lower  border  of  the  coronary  sinus.     The  oblique  vein  descends 


64 


THORAX 


on  the  posterior  wall  of  the  left  atrium  and  ends  in  the  upper 
border  of  the  sinus;  and  the  small  cardiac  vein  (O.T.  right 
coronary)  runs  along  the  lower  margin  of  the  heart  with  the 
marginal  branch  of  the  right  coronary  artery,  curves  round 
the  right  border  of  the  heart,  in  the  coronary  sulcus,  ends  in 
the  right  extremity  of  the  coronary  sinus.    The  anterior  cardiac 


—  Superior  vena  cava 


Reflection  of  serous  pericardium 


Right  atrio- 
ventricular openins; 


Right  auricle 
Interatrial  furrow 
Left  atrium 


Left  auricle 


Crista  terminalis 

Fossa  ovalis 

Valve  of  inferior 
vena  cava 

Inferior  vena  cava 


Left  atrio- 
ventricular opening 


Coronary  sinus 


Fig.  31. — The  Anterior  Aspect  of  the  Atrial  Part  of  the  Heart.  The 
atria  have  been  removed  from  the  ventricles.  The  ventricular  portion 
of  the  same  heart  is  depicted  in  Fig.  28.  The  specimen  was  hardened 
in  situ. 


veins  are  small  vessels  which  ascend  along  the  anterior  surface 
of  the  right  ventricle  and  terminate  directly  in  the  lower  and 
anterior  part  of  the  right  atrium.  The  vencB  cordis  mini7n(E  are 
small  veins  which  pass  from  the  substance  of  the  heart,  and 
more  particularly  from  the  walls  of  the  right  atrium  and 
ventricle,  and  open,  by  small  orifices,  into  the  cavity  of  the 
right  atrium.  The  orifice  through  which  the  great  cardiac 
vein  opens  into  the  coronary  sinus  is  usually  provided  with  a 
valve ;  the  orifice  of  the  small  cardiac  vein  may  be  provided 


THORACIC  CAVITY  65 

with  a  valve,  but  the  orifices  of  the  other  tributaries  of  the 
sinus  are  generally  devoid  of  valves. 

Cardiac  Nerves. — The  coronary  plexuses,  from  which  the 
nerve  supply  of  the  heart  is  directly  derived,  are  offshoots  of  the 
superficial  and  deep  cardiac  plexuses,  which  will  be  dissected 
later  (pp.  85  and  100).  The  nght  coronary  plexus  is  formed  by 
twigs  from  the  superficial  cardiac  plexus  which  descend  along 
the  pulmonary  artery,  and  by  additional  fibres  from  the  deep 
cardiac  plexus.  It  is  distributed  along  the  course  of  the  right 
coronary  artery.  The  left  coronary  plexus^  which  accompanies 
the  artery  of  the  same  name,  is  derived  from  the  deep 
cardiac  plexus.  The  nerves  do  not  slavishly  follow  the 
arteries ;  they  soon  leave  the  vessels,  and  are  ultimately 
lost  in  the  substance  of  the  heart.  Here  and  there  ganglia 
are  developed  in  connection  with  them. 

Dissection. — The  chambers  of  the  heart  and  the  great  vessels  which 
communicate  with  them  should  now  be  examined,  as  far  as  possible  whilst 
the  heart  is  still  m  situ,  so  that  the  relations  of  the  various  orifices  to 
the  sternum  and  costal  cartilages  can  be  verified.  Examine  first  the  right 
atrium  and  the  venae  cavae,  then  the  right  ventricle  and  the  pulmonary- 
artery,  and  afterwards  the  left  ventricle  and  the  ascending  part  of  the 
aorta,  which  springs  from  it.  The  examination  of  the  left  atrium,  and 
the  terminations  of  the  pulmonary  veins,  cannot  be  conveniently  undertaken 
until  the  heart  and  the  pericardium  have  been  removed  from  the  body 
(see  p.  89). 

Atrium  Dextrum  (O.T.  Right  Auricle). — Open  the  right 

atriu?fi  by  means  of  the  following  incision.  Enter  the  knife 
at  the  apex  of  the  auricle  (O.T.  auricular  appendix)  and  carry 
it  posteriorly,  close  to  the  upper  border  of  the  auricle,  across 
the  sulcus  terminalis  and  through  the  lateral  wall  of  the  atrium, 
to  the  posterior  border  of  the  lower  end  of  the  superior  vena 
cava;  then  downwards,  posterior  to  the  sulcus  terminalis,  to  the 
inferior  vena  cava ;  and  finally  anteriorly,  across  the  lower  end 
of  the  sulcus  terminahs  and  above  the  anterior  aspect  of  the 
lower  end  of  the  inferior  vena  cava,  to  the  coronary  sulcus. 
Throw  the  flap  thus  formed  anteriorly,  and  clean  the  interior 
of  the  cavity  with  a  sponge. 

As  the  flap  is  turned  anteriorly  a  vertical  muscular  bundle 
will  be  noted  on  its  inner  surface.  This  is  the  crista  terminalis^ 
which  corresponds  in  position  with  the  sulcus  terminalis  on 
the  outer  surface.  It  marks  the  boundary  between  the 
anterior  part,  the  atrium,  and  the  posterior  part,  which 
is    known    as   the  venous  sinus  because  the  great  veins   of 

VOL.  II — 5 


66  THORAX 

the  body  and  heart  open  into  it.  These  two  parts  of  the 
cavity  differ,  however,  not  only  in  position  and  their  relations 
to  the  great  veins,  but  also  in  the  characters  of  their  walls. 
The  whole  of  the  interior  of  the  atrium  presents  a  poHshed 
glossy  appearance,  due  to  the  endocardial  Hning;  but  whilst  the 
wall  of  the  venous  sinus  is  smooth,  the  rest  of  the  wall  of  the 
atrium  is  rendered  rugose  by  a  large  number  of  muscular  ridges 

Aorta 
Superior  vena  cava 


I  jbwk        m      M^' ^^^^^tr^T^  J^y^'V  *M^^M^Kkt.        Crista 

Upper  right,  ,i.,„    ,^      ,J  ..j^M^Bm^rilf^'  f  <  €jPWky  terminalis 
pulmonarj'  vein 


Lower  right    ^ 
pulmonary 
vein 


Limbus  fossse  ovalis 


Fossa  ovalis 


\  Tricuspid  orifice 

Opening  of  coronary  sinus 


Inferior  vena  cava 

Valve  of  the  inferior 
vena  cava  (Eustachian)     Valve  of  the  coronary  sinus  (Thebesian) 


Fig.  32. — The  Right  Atrium.      Part  of  the  posterior  wall  and  the  whole 
of  the  right  lateral  and  anterior  walls  have  been  thrown  anteriorly. 

which  commence  at  the  crista  terminalis  and  run  anteriorly  to 
the  right  margin  of  the  atrium.  These  bundles,  on  account 
of  their  somewhat  parallel  arrangement,  are  called  the  musculi 
pectinati. 

The  veins  which  open  into  the  right  atrium  are  the  (i) 
superior  vena  cava,  (2)  inferior  vena  cava,  (3)  coronary  sinus, 
(4)  anterior  cardiac  veins,  and  (5)  venae  cordis  minimse.  The 
aperture  by  which  the  blood  leaves  it  is  the  tricuspid  orifice. 

The  orifice  of  the  superior  vena  cava  is  in  the  upper  and 
posterior  part  of  the  atrium,  at  the  level  of  the  third  right  costal 


THORACIC  CAVITY 


67 


cartilage.  It  is  entirely  devoid  of  any  valvular  arrangement. 
Immediately  below  it  on  the  posterior  wall  of  the  atrium,  in 
a  well -fixed  heart,  will  be  found  a  rounded  prominence, 
the  interve?ious  tubei-cle  (Lower),    which   tends   to    throw    the 


Pericardium 


Superior  vena  cava 


Musculi  pectinati 
Crista  terminalis 


Diaphragm 


Vena  az>- gos 


Right 
bronchus 


Right 

^hi^_^ pulmonary 

artery 

Bronchial 

gland 

Pulmonary 
veins 


Venous  sinus 
of  right  atrium 


Inferior  vena 
cava 

Hepatic  vein 


Pig.  33. — Sagittal  section  through  the  Right  Atrium  of  the  Heart  and 
the  Root  of  the  Right  Lung. 

Stream  of  blood  entering  the  atrium  by  the  superior  vena 
cava  downwards  and  anteriorly  into  the  atrio-ventricular  orifice. 
The  orifice  of  the  ijiferior  vena  cava  is  in  the  lower  and 
posterior  part  of  the  atrium,  at  the  level  of  the  sixth  right  costal 
cartilage  and  the  lower  border  of  the  eighth  thoracic  vertebra. 
Running  along  its  anterior  margin,  and  intervening  between  it 
and  the  atrio-ventricular  opening,  is  the  remnant  of  a  valve, 
the  valve  of  the  vena  cava  (Eustachian).  It  terminates,  to  the 
left,  in  the  lower  end  of  a  muscular  ridge,  limbus  fosses  ovalis 


68 


THORAX 


Orifice  of  superior 
vena  cava 


(O.T.  annulus  ovalis),  which  lies  on  the  inter-atrial  septum 
and  forms  the  anterior  and  upper  boundary  of  a  shallow 
fossa,  the  fossa  ovalis.  At  the  upper  end  of  this  fossa  there 
was,  during  foetal  life,  a  foramen,  tht  foramen  ovale,  through 

which  the  two  atria 

Superior  vena  cava  COmmunicatcd  with 

each   other.      The 

g^ Right  auricle  (O.T.  appendix)    objCCt    of  the  ValvC 

of  the  vena  cava, 
which  in  foetal  life 
was  much  more 
perfect,  was  to  di- 
rect the  oxygenated 
inferior  caval  blood 
through  the  fora- 
men ovale  into  the 
left  atrium,  whence 
it  was  passed  into 
the  left  ventricle, 
and  was  then  dis- 
tributed, by  the 
aorta,  throughout 
the  whole  system. 

During  foetal  life  it 
would  have  been  use- 
less to  pass  the  blood 
through  the  lungs, 
which  were  inactive  and 
devoid  of  air.  At  the 
same  time,  had  the 
oxygenated  blood  been 
passed      through      the 


Crista  terminalis 


Intervenous 
tubercle 

Limbus  ovalis 


Fossa  ovalis 

Left  atrio- 
ventricular orifice 

Opening  of 
coronary  sinus 

Coronary  valve 

Inferior 
caval  valve 
(Eustachian) 


Cut  edge  of 
atrial  wall 
Inferior  vena  cava 


Fig.  34. — Interior  of  Right  Atrium  as  seen  by  the 
removal  of  the  anterior  wall,  or  that  wall  op- 
posed to  the  base  of  the  Ventricles.      This  is 

a  part  of  the  same  specimen  that  is  depicted    right   atrium   into   the 
in  Fig.  31.  right  ventricle,  it  would 

have  failed  to  reach 
the  head  and  the  upper  extremities,  for,  leaving  the  right  ventricle  by  the 
pulmonary  artery,  it  would  have  entered  the  aorta  through  the  ductus 
arteriosus  beyond  the  origin  of  the  left  subclavian  artery  and,  therefore, 
beyond  the  innominate  and  left  common  carotid  arteries. 

In  many  cases  a  small  part  of  the  foramen  ovale  persists 
in  the  adult.  If  it  is  present  it  will  be  found  on  the  left  of 
the  upper  curved  end  of  the  limbus  ovalis. 

The  opening  of  the  coronary  sinus  lies  to  the  left  of  the  lower 
end  of  the  limbus  ovalis  and  directly  posterior  to  the  tricuspid 
orifice.     On  its  right  margin  lies  a  valvular  fold,  the  valve  of 


THORACIC  CAVITY  69 

the  coronary  siiius  (O.T.  Thebesian),  which  turns  the  blood, 
flowing  from  left  to  right  in  the  sinus,  anteriorly  into  the  atrio- 
ventricular orifice.  The  venae  minimae  cordis  and  the  anterior 
cardiac  veins  open  directly  into  the  atrium  by  small  orifices 
scattered  irregularly  over  the  walls. 

The  tricuspid  orifice  is  in  the  lower  and  anterior  part  of  the 
atrium.  It  opens  anteriorly  into  the  lower  and  posterior  part  of 
the  cavity  of  the  right  ventricle,  and  is  sufficiently  large  to 
admit  the  tips  of  three  fingers.  It  is  bounded  by  a  fibrous 
ring  to  which  the  cusps  of  the  right  atrio-ventricular  valve  are 
attached.  These  cusps  will  be  examined  when  the  right 
ventricle  is  opened. 

Pulmonary'  artery  Aorta 

^j^==::r^~,.^   I  Right  end  of  transverse  sinus 
Left  coronary       ^^^^jg^  '    ^'^^^  coronary  artery 
arterj-  ./j1^^^BBl''''i5?^s3^^      auricle 
Left  end  of 
transverse  sinus 
Left  auricle 


Left  atrium  ^        Right  atrium 

T  .  ,         -''^    ■ — "^  Transverse  sinus 

Inter-atrial  septum 

Fig.  35. — Transverse  section  through  the  Upper  Part  of  the  Heart. 

The  Septum  Atriorum  and  the  Fossa  Ovalis. — The  inter- 
atrial septum  is  a  fibro-muscular  partition  which  intervenes 
between  the  right  and  left  atria.  In  the  foetus  it  is  pierced 
by  an  obliquely  directed  foramen,  the  foramen  ovale,  already 
referred  to ;  and  in  the  adult  it  is  marked  on  the  lower  and 
posterior  part  of  its  right  side  by  a  shallow  depression,  the  fossa 
ovalis^  which  is  bounded  anteriorly  and  above  by  a  muscular 
ridge,  the  limbus  ovalis^  whilst  below  and  posteriorly  it  fades 
away  into  the  orifice  of  the  inferior  vena  cava. 

The  floor  of  the  fossa  ovalis  is  very  thin ;  it  marks  the 
situation  of  the  lower  part  of  the  foramen  ovale  of  the  foetus, 
and  is  formed  by  a  portion  of  the  inter-atrial  wall  which, 
during  foetal  life,  acted  as  a  flap  valve  and  prevented  regurgi- 
tation of  blood  from  the  left  to  the  right  atrium. 

The  Vena  Cava  Superior. — The  superior  vena  cava  returns 
to  the  right  atrium  the  blood  from  the  head  and  neck,  the 

II — ha 


70  THORAX 

upper  extremities,  the  wall  of  the  thorax,  and  the  upper  parts 
of  the  walls  of  the  abdomen.  It  commences,  by  the  union 
of  the  right  and  left  innominate  veins,  at  the  level  of  the 
lower  border  of  the  sternal  end  of  the  right  first  costal 
cartilage  ;  and  it  terminates,  in  the  upper  and  posterior  part  of 
the  right  atrium,  at  the  level  of  the  right  third  costal  cartilage, 
about  half  an  inch  from  the  right  border  of  the  sternum. 
It  lies  partly  in  the  superior  and  partly  in  the  middle 
mediastinum,  and  its  lower  half  is  within  the  fibrous  pericardium 
and  is  partly  ensheathed  by  the  serous  pericardium. 

Tributaries. — The  tributaries  of  the  superior  vena  cava  are 
the  two  innominate  veins,  by  whose  junction  it  is  formed, 
and  the  vena  azygos,  which  enters  it  immediately  before 
it  pierces  the  fibrous  pericardium,  at  the  level  of  the  second 
right  costal  cartilage. 

Relations. — The  superior  vena  cava  lies  to  the  right  of, 
and  somewhat  posterior  to,  the  ascending  aorta.  Posterior  to 
its  upper  part  are  the  right  pleura  and  lung  on  the  right, 
and  the  right  vagus  and  the  vena  azygos  on  the  left,  and,  at 
a  lower  level,  the  right  bronchus,  the  right  pulmonary  artery, 
and  the  upper  right  pulmonary  vein.  Anteriorly  and  on  the 
left  it  is  overlapped  by  the  ascending  aorta,  and  on  the  right 
by  the  right  pleura  and  lung.  On  its  left  side  above  is  the 
lower  end  of  the  innominate  artery,  and  below  is  the  ascending 
aorta ;  and  on  the  right  side  is  the  right  pleura,  with  the  right 
phrenic  nerve  and  the  accompanying  vessels  intervening. 

The  Thoracic  Part  of  the  Inferior  Vena  Cava. — Only  a 
small  portion,  about  three-quarters  of  an  inch,  of  the  inferior 
vena  cava  is  found  in  the  thorax.  It  ascends  from  the 
diaphragm  along  the  mediastinal  surface  of  the  right  pleura 
and  lung,  pierces  the  pericardium  anterior  to  the  lower 
border  of  the  right  ligamentum  pulmonis,  and  immediately  * 
ends  in  the  lower  and  posterior  angle  of  the  right  atrium. 

Relations. — Anterior  to  it  is  the  diaphragm ;  posterior  to  it 
the  vena  azygos,  the  splanchnic  nerves  and  the  thoracic  duct ; 
and  to  its  right  the  phrenic  nerve  with  its  accompanying 
vessels  and  the  right  pleura  and  lung  (see  Fig.  12). 

Ventriculus  Dexter. — The  cavity  of  the  right  ventricle 
should  be  opened  by  three  incisions.  The  first  should  be 
made  transversely  across  the  upper  end  of  the  conus  arteriosus, 
immediately  below  the  commencement  of  the  pulmonary 
artery.      It   should   begin   a   little  to  the  right  of  the  upper 


THORACIC  CAVITY 


71 


end  of  the  anterior  longitudinal  sulcus  and  terminate  a 
little  to  the  left  of  the  coronary  sulcus.  The  second  must 
commence  at  the  right  end  of  the  first  and  pass  obliquely 
downwards  and  to  the  right,  along  the  left  margin  of  the 
coronary  sulcus,  to  the  lower  border  of  the  heart.  The  third 
commences  at  the  left  end  of  the  first,  follows  the  line  of  the 
anterior  inter-ventricular  sulcus,  lying  a  little  to  its  right  side, 


Superior  vena  cava      ^^ 


Innominate  artery 
Left  subclavian  artery 
Left  common  carotid  artery 


Aortic  arch 
Serous  pericardium 

Ascending  a6rta 
Pulmonary  artery 


Right  auricle  (O.T.  appendix) 

Left  anterior  pulmonary 
sinus  (Valsalva) 
Pulmonary  valve 


Conus  arteriosus 


Anterior  segment  of 
tricuspid  valve 


Medial  segment 

Anterior  papillary 
muscle 
-  Moderator  band 


Inferior  vena  cava 

Inferior  segment  of  tricuspid  valve 

Fig.  36.  — The  Interior  of  the  Right  Ventricle. 

and  also  terminates  at  the  lower  margin  of  the  heart.  After 
the  triangular  flap  thus  formed  is  turned  downwards  and  to 
the  right,  the  cavity  of  the  ventricle  should  be  cleaned  with 
the  aid  of  sponge  and  forceps.  If  the  moderator  band  of 
muscle  fibres,  which  connects  the  anterior  wall  of  the  ventricle 
with  the  inter-ventricular  septum,  interferes  with  the  necessary 
displacement  of  the  flap,  it  must  be  divided. 
-  The  cavity  of  the  right  ventricle  has  a  triangular  outline. 
The  atrio-ventricular  orifice  opens  into  the  lower  and  posterior 
angle,  the  pulmonary  artery  springs  from  the  upper  and 
II— 5  & 


72 


THORAX 


anterior  angle,  and  between  the  two  orifices  is  a  strong  and 
rounded  muscular  ridge,  the  supra -ventricular  ridge.  This 
projects  into  the  cavity  converting  it  into  a  U-shaped  tube 
which  commences  posterior  to  and  below  the  supra-ventricular 
ridge,  runs  anteriorly  and  to  the  left,  towards  the  apex,  and 
turns  upwards  and  anteriorly,  along  the  anterior  part  of  the 
inter-ventricular  septum  and  anterior  to  the  supra-ventricular 
ridge,  to  the  orifice  of  the  pulmonary  artery. 

On     transverse     section 
the  cavity  of  the  right  ven- 
tricle is  semilunar  in  outline, 
in  consequence  of  the  thick 
inter  -  ventricular      septum, 
which    forms   the    left   and 
posterior  wall,  bulging  into 
the   cavity   (Fig.    37).      Its 
walls     are     much     thicker 
than  the  walls  of  the  right 
Fig.  37.— Transverse  section  through   atrium,    but    much   thinner 
the   Ventricular    Part    of   the    Heart    than    the    walls    of    the    left 
seen  from  above.      (From  Luschka. )     ventricle     (Fig.     41).        The 

reason  for  these  differences 
is  obvious  :  the  auricle  has 
merely  to  force  the  blood 
through     the     wide     atrio- 

6.  Inferior       longitudinal       (inter -ven-     yCntricular    OrificC    iutO     the 

tricular)  sulcus  with  middle  cardiac  •    i   .             ,    •    i              j    .  i          •    ^  ^ 

vein  and  inferior  branch  of  right  I^^g^t  VCntricle,  and  the  right 

coronary  artery.  VCntriclc    haS     Only    tO    SCud 

7.  Anterior       longitudinal      (inter -ven-  ^l^g  bloo(^   thrOUgh  the  luUgS 

tricular)  sulcus  with  great  cardiac  U       i    f  '  U  u 

vein    and    anterior   branch    of  left     ^O    the    IClt  atriUm  ',     but    the 
coronary  artery.  left     VCntriclc     haS     tO     forCC 

the  blood  through  the  whole 
of  the  body,  the  head  and  neck,  and  the  limbs;  and  the 
muscular  strength  of  the  walls  of  the  cavities  of  the  heart  is 
proportional  to  the  work  they  have  to  do. 

The  portion  of  the  right  ventricle  which  ascends  to  the 
orifice  of  the  pulmonary  artery  is  the  conus  arteriosus.  Its 
walls  are  smooth  and  devoid  of  projecting  muscular  bundles, 
but  the  inner  surface  of  the  walls  of  the  remaining  part  of  the 
ventricle  is  rendered  extremely  irregular  by  the  projection  of 
a  lace-work  of  fleshy  ridges  called  trabeculce.  carnece.  Some 
of  the  trabeculse  are  merely  ridges  raised  in  relief  upon  the 


Cavity  of  right  ventricle. 
Cavity  of  left  ventricle. 
Ventricular  septum. 
Thick  wall  of  left  ventricle. 
Thinner  wall  of  right  ventricle. 


THORACIC  CAVITY  73 

surface ;  others  are  attached  to  the  wall  at  each  extremity, 
but  are  free  in  the  rest  of  their  extent.  The  cavity  of  the 
ventricle  is  invaded,  however,  not  only  by  the  trabeculae 
carneae,  but  also  by  a  number  of  conical  muscular  projections, 
the  viusculi  papillares.  These  are  attached  by  their  bases  to 
the  walTof  the  ventricle,  whilst  their  apices  are  connected, 
by  a  number  of  tendinous  strands,  to  the  margins  and  the 
ventricular  surfaces  of  the  cusps  of  the  atrio-ventricular  valve. 
As  a  rule  there  is  one  large  anterior  papillary  muscle  attached 
to  the  anterior  wall,  a  large  inferior  papillary  muscle  attached 
to  the  inferior  wall,  and  a  number  of  smaller  papillary  muscles 
attached  to  the  septal  wall.  Occasionally  the  anterior  and 
inferior  muscles  are  represented  by  a  number  of  smaller 
projections.  It  must  be  noted  that  the  chordae  tendineae 
from  each  papillary  muscle,  or  group  of  papillary  m.uscles, 
gain  insertion  into  the  margins  and  ventricular  surfaces  of 
two  adjacent  cusps  of  the  valve.  The  result  of  this  arrange- 
ment is,  as  the  papillary  muscles  contract  simultaneously  with 
the  contraction  of  the  general  wall  of  the  ventricle,  that  the 
chordae  tendineae  hold  the  margins  of  the  cusps  together  and 
prevent  them  being  driven  backwards  into  the  atrium. 

One  of  the  trabeculae  carnea3,  which  is  usually  strong  and 
well  marked,  passes  across  the  cavity  from  the  septum  to  the 
base  of  the  anterior  papillary  muscle.  This  is  the  juoderator 
band.  It  tends  to  prevent  over-distension  of  the  cavity  of 
the  ventricle,  by  fixing  the  more  yielding  anterior  w^all  of  the 
ventricle  to  the  more  solid  septum. 

There  is  one  opening  of  entrance  into  the  right  ventricle, 
the  atrio-ventricular,  and  one  opening  of  exit,  the  pulmonary 
orifice.      Each  is  guarded  by  a  valve. 

The  right  atrio-ventricular  orifice  lies  at  the  lower  and 
posterior  part  of  the  right  ventricle,  its  centre  being  behind 
the  middle  of  the  sternum  at  the  level  of  the  fourth  intercostal 
space.  It  is  about  one  inch  in  diameter,  and  is  surrounded 
by  a  fibrous  ring.  It  admits  the  tips  of  three  fingers, 
and  it  is  guarded  by  a  valve  possessing  three  cusps,  an 
anterior,  a  medial,  and  an  inferior.  The  anterior  cusp 
intervenes  between  the  atrio-ventricular  orifice  and  the  conus 
arteriosus.  The  medial  cusp  lies  in  relation  with  the  septal 
w^all ;  and  the  inferior  cusp  with  the  inferior  wall  of  the 
ventricle. 

The  bases  of  the  cusps  are  attached  to  the  fibrous  ring 


74 


THORAX 


round  the  margin  of  the  orifice.  Their  apices,  margins, 
and  ventricular  surfaces  are  attached  to  the  chordae  tendinese. 
Their  auricular  surfaces,  over  which  blood  flows  as  it  enters 
the  ventricle,  are  smooth,  and  their  ventricular  surfaces  are 
more  or  less  roughened  by  the  attachment  of  the  chordae 
tendinese,  but  the  roughening  is  less  marked  on  the  ventricular 
surface  of  the  anterior  cusp  over  which  the  blood  flows  as  it 
passes  through  the  conus  arteriosus  to  the  pulmonary  orifice. 

Pulmonary  artery         Posterior  cusp  of  pulmonary  valve 


Aorta 


Supra- ventricular  crest 
,  Pars  nrembranacea  septi 


Right  auricle 


Left  segment  of  atrio-ventricular  bundle  I 

Right  segment  of  atrio-ventricular  bund 

Moderator  band 

Base  of  anterior 
papillary  muscle 

Fat  in  sulcus  longl- 
tudinalis  anterior 

Left  ventricl 


Coronary  sulcus 

Coronary  valve 

Opening  of  coronary  sinus 
Base  of  medial  cusp  of  tricuspid  valve 


Medial  cusp  of  tricuspid  valve 
Atrio-ventricular  bundle 


Fig.  38. — Dissection  of  the  Right  Ventricle  showing  the  Atrio- 
ventricular Bundle. 


The  Atrio-ventricular  Btmdle.  — The  atrio-ventricular  bundle  is  a  small 
bundle  of  peculiar  muscle  fibres,  of  pale  colour,  which  forms  the  only  direct 
muscular  connection  between  the  walls  of  the  atria  and  the  ventricles  (see 
p.  92).  To  expose  this  bundle,  the  anterior  part  of  the  medial  cusp  of  the 
tricuspid  valve  must  be  detached  from  the  fibrous  atrio-ventricular  ring. 
When  this  has  been  done,  the  pars  membranacea,  or  upper  fibrous  part  of 
the  inter-ventricular  septum  will  be  exposed,  and  the  atrio-ventricular 
bundle  will  be  found  running  along  its  posterior  and  lower  border  to  the 
upper  end  of  the  muscular  part  of  the  septum,  where  it  divides  into  right 
and  left  branches.  The  right  branch  runs  along  the  right  side  of  the 
septum  to  the  moderator  band,  along  which  it  passes  to  the  anterior 
papillary  muscle.     The  left  branch  passes  between  the  pars  membranacea 


THORACIC  CAVITY  75 

and  the  upper  end  of  the  muscular  part  of  the  septum,  and  then  descends 
along  the  left  side  of  the  septum.  Both  branches  send  off  numerous  rami- 
fications which  are  distributed  to  the  various  parts  of  the  walls  of  the 
ventricles. 

The  pulmonary  orifice  lies  at  the  upper,  anterior,  and  left 
part  of  the  ventricle,  at  the  apex  of  the  conus  arteriosus.  Its 
centre  is  behind  the  third  left  costal  cartilage  immediately  to 
the  left  of  the  left  border  of  the  sternum,  and  its  margin  is 
surrounded  by  a  thin  fibrous  ring  to  which  the  bases  of  the 
three  semilunar  cusps  of  the  pulmonary  valve  are  attached. 

Dissection. — Note  that  immediately  above  its  commencement  the  wall 
of  the  pulmonary  artery  shows  three  distinct  bulgings  ;  these  are  the 
pulmonary  sinuses  (Valsalva)  of  which  two  are  anterior,  and  the  third  is 
situated  posteriorly.  Make  a  transverse  incision  across  the  wall  of  the 
pulmonary  artery  immediately  above  the  dilatations,  and  from  each  end  of 
the  transverse  incision  make  a  vertical  incision  upwards  towards  the  arch 
of  the  aorta  ;  raise  the  flap  so  formed  and  examine  the  cusps  of  the  valve 
from  above. 

The  Pulmonary  Valve. — Each  cusp  of  the  valve  is  of  semi- 
lunar form.  •  Its  upper  or  arterial  surface  is  concave,  its 
lower  or  ventricular  surface  is  convex ;  and  it  consists  of  a 
layer  of  fibrous  tissue  covered,  on  each  surface,  by  a  layer  of 
endothelium.  The  fibrous  basis  of  the  cusp  is  not  equally 
thick  in  all  parts.  A  stronger  band  runs  round  both  the  free 
and  the  attached  margin.  The  centre  of  the  free  margin  is 
thickened  to  form  a  small  rounded  mass — the  7iodulus  of  the 
valve — and  the  small  thin  semilunar  regions  on  each  side  of 
the  nodule  are  called  the  hmulcB  of  the  valve.  When  the 
ventricular  contraction  ceases,  and  the  elastic  reaction  of  the 
wall  of  the  pulmonary  artery  forces  the  blood  backwards 
towards  the  ventricle,  the  cusps  of  the  valve  are  forced  into 
apposition  ;  the  nodules  meet  in  the  centre  of  the  lumen  -,  the 
ventricular  surfaces  of  the  lunulse  of  adjacent  cusps  are  com- 
pressed against  each  other,  and  their  free  margins  project 
upwards  into  the  cavity  of  the  artery,  in  the  form  of  three 
vertical  ridges  which  radiate  from  the  nodules  to  the  wall  of 
the  artery.  Regurgitation  of  blood  into  the  ventricle  is  thus 
effectually  prevented. 

The  dissector  may  readily  demonstrate  the  general  appear- 
ance of  the  cusps  and  their  relationship  to  each  other  by 
packing  the  concavity  of  each  cusp  with  cotton  wool. 

Arteria  Pulmonalis. — -The  pulmonary  artery  lies  within 
the  fibrous  pericardium,  and  is  enclosed,  with  the  ascending 


76  THORAX 

part  of  the  aorta,  in  a  common  sheath  of  the  serous 
pericardium.  It  commences  at  the  upper  end  of  the  conus 
arteriosus,  posterior  to  the  sternal  extremity  of  the  third  left 
costal  cartilage.  It  is  about  two  inches  long,  and  it  runs  up- 
wards and  posteriorly  into  the  concavity  of  the  aortic  arch,  where 
it  bifurcates  into  two  branches.  The  bifurcation  takes  place 
posterior  to  the  sternal  end  of  the  left  second  costal  cartilage. 
Relatio7is. — At  its  commencement  it  is  placed  anterior  to 
the  lower  end  of  the  ascending  aorta,  but  as  it  runs  upwards 
and  posteriorly  it  passes  to  the  left  side  of  the  latter  vessel, 
and  lies  anterior  to  the  upper  part  of  the  anterior  wall  of  the 
left  atrium,  from  which  it  is  separated  by  the  transverse  sinus 
of  the  pericardium.  Anterior  to  it  is  the  upper  part  of  the 
anterior  wall  of  the  pericardium,  which  separates  it  from  the 
anterior  part  of  the  mediastinal  surface  of  the  left  pleura  and 
lung.  To  its  right  side,  below,  are  the  right  coronary  artery 
and  the  apex  of  the  right  auricle,  and  above  is  the  ascending 
aorta.  To  its  left  side  lie  the  left  coronary  artery  and  the 
anterior  end  of  the  left  auricle. 

Dissection. — Cut  away  the  anterior  wall  of  the  pulmonary  artery  up  to 
the  level  of  its  bifurcation  and  pass  probes  into  its  right  and  left  branches. 
Note  that  the  right  branch  runs  transversely  to  the  right,  and  that  the  left 
branch  runs  posteriorly  and  to  the  left. 

The  right  pulmonary  artery  commences  at  the  bifurcation 
of  the  pulmonary  stem,  below  the  arch  of  the  aorta.  As 
it  runs  to  the  right,  towards  the  hilus  of  the  right  lung,  along 
the  upper  border  of  the  left  atrium  and  the  transverse  sinus 
(Figs.  2  1  and  27),  it  passes  posterior  to  the  ascending  aorta 
and  the  superior  vena  cava,  and  anterior  to  the  oesophagus 
and  the  stem  of  the  right  bronchus.  It  enters  the  hilus  of 
the  lung  below  the  eparterial  branch  of  the  bronchus,  above 
and  posterior  to  the  upper  right  pulmonary  vein,  and  it 
descends,  in  the  substance  of  the  lung,  on  the  postero-lateral 
side  of  the  stem  bronchus,  and  between  its  ventral  and  its 
dorsal  branches,  where  it  will  be  dissected  at  a  later  period 
(p.  98). 

Branches. — As  it  enters  the  hilus  of  the  lung  it  gives  oif  a 
branch  which  accompanies  the  eparterial  bronchus,  and  as  it 
descends  in  the  substance  of  the  lung  it  gives  off  branches 
which  correspond  with  the  branches  of  the  stem  bronchus 
(see  p.  98). 

The   left  pulmonary    artery   runs    posteriorly   and    to    the 


THORACIC  CAVITY 


77 


left,  across  the  anterior  aspect  of  the  descending  aorta  and  the 
left  bronchus,  to  the  hilus  of  the  left  lung.  It  is  covered  an- 
teriorly and  on  the  left  by  the  anterior  part  of  the  mediastinal 
surface  of  the  left  pleural  sac.  As  it  descends  in  the  sub- 
stance of  the  lung  it  lies  along  the  postero-Iateral  aspect 
of  the  stem  bronchus  and  between  its  ventral  and  dorsal 
branches  (p.  98). 

Branches. — Except  that   it  has  no  branch  corresponding 
with  that  which  accompanies  the  eparterial  bronchus  on  the 


Left  common  carotid  artery^ 
Left  innominate  vein 


Right  auricle 
Stem  of  pulmonary  artery 

Pulmonary  valve 
Upper  left  pulmonary  vein 
Left  auricle   -- 


Right  innominate  vein 
Innominate  artery 

Left  subclavian 
artery 

,   Arch  of  aorta 

Vena  azygos 

Aorta 

~-  Ductus  arteriosus 

Left  pulmonary 
artery 

Lower  left  pulmon- 
ary vein 

Descending  aorta 


Inferior  vena  cava 

Fig.  39. — Dissection  of  the  Heart  and  Great  Vessels  of  a  Foetus,  showing 
the  angular  junction  of  the  Ductus  Arteriosus  with  the  Aorta. 

right   side,   the    branches   of  the   left   pulmonary   artery   are 
similar  to  those  given  off  by  the  right  pulmonary  artery. 

Ligamentum  Arteriosum. — The  ligamentum  arteriosum  is 
a  strong  fibrous  band  which  connects  the  commencement  of 
the  left  pulmonary  artery  with  the  lower  surface  of  the  arch  of 
the  aorta.  It  is  the  remains  of  the  walls  of  a  wide  channel, 
the  ductus  arteriosus^  which  united  the  left  pulmonary  artery 
with  the  aorta  throughout  the  whole  period  of  pre-natal  life. 

During  foetal  life  the  lungs  had  no  aerating  function  ;  therefore  the  right 
puhnonary  artery  and  the  part  of  the  left  pulmonary  artery  beyond  the 
origin  of  the  ductus  arteriosus  were  small,  for  they  had  merely  to  convey 
sufficient  blood  to  maintain  the  life  and  growth  of  the  non-functional  lungs. 
At  this  period,  therefore,  the  blood  which  had  entered  the  right  ventricle, 


7  8  THORAX 

'  » 

through  the  superior  vena  cava  and  the  right  auricle  (see  p.  68),  was  ejected, 
by  the  ventriclCj  into  the  pulmonary  artery  and  the  greater  part  of  it  passed 
through  the  ductus  arteriosus  into  the  aorta,  which  it  entered  beyond  the 
origin  of  the  left  subclavian  artery,  and  there  mingled  with  the  more 
oxygenated  blood  from  the  placenta,  the  lower  part  of  the  body,  and  the 
lower  limbs,  which  passed  from  the  inferior  vena  cava  through  the  right 
atrium  and  the  foramen  ovale  to  the  left  atrium,  and  thence  to  the  left 
ventricle  by  which  it  was  pumped  into  the  aorta. 

It  is  obvious  that  the  passage  of  blood  from  the  pulmonary  artery  into 
the  aorta  could  take  place  only  so  long  as  the  pressure  in  the  pulmonary 
artery  was  greater  than  the  pressure  in  the  aorta.  At  birth,  when  the 
blood  rushed  through  the  rajDidly  enlarged  right  and  left  pulmonary  arteries 
into  the  lungs,  as  they  expanded  with  the  first  respiratory  efforts,  the  pres- 
sure in  the  pulmonary  artery  and  the  ductus  arteriosus  was  reduced  below 
that  in  the  aorta,  and  the  blood  in  the  aorta  would  have  flowed  into  the 
ductus  arteriosus  had  it  not  been  that  the  angle  of  union  between  the 
ductus  arteriosus  and  the  aorta  had  become  more  and  more  acute  during 
the  latter  part  of  foetal  life,  with  the  result  that  the  upper  and  right  margin 
of  the  orifice  of  communication  attained  a  position  overhanging  the  lower 
and  left  margin  (Fig.  39)  ;  and  as  soon  as  the  blood  pressure  in  the  aorta 
exceeded  that  in  the  ductus  arteriosus,  this  margin,  acting  as  a  flap  valve, 
was  driven  against  the  left  and  lower  margin,  closing  the  orifice  effectually. 
After  this  occurred  the  utility  of  the  ductus  arteriosus  terminated,  and  it  was 
converted  into  a  fibrous  cord — the  ligamentum  arteriosum. 

Note  that  the  left  recurrent  nerve  curves  round  the 
lower  surface  of  the  aortic  arch  on  the  left  side  of  the  upper 
end  of  the  ligamentum  arteriosum,  and  that  the  superficial 
cardiac  plexus  lies  below  the  aortic  arch  immediately  to  the 
right  of  the  ligament. 

In  a  few  cases  the  ductus  arteriosus  remains  patent  for 
several  years  of  life  after  birth,  and  occasionally  it  is  patent 
throughout  the  whole  of  life. 

Dissection. — Cut  through  the  remains  of  the  upper  part  of  the  conus 
arteriosus  immediately  below  the  bases  of  the  cusps  of  the  pulmonary  valve, 
and  carefully  dissect  the  upper  part  of  the  conus  and  the  lower  part  of  the 
pulmonary  artery  away  from  the  front  of  the  commencement  of  the  ascending 
aorta.  When  this  has  been  done,  turn  the  lower  end  of  the  pulmonary 
artery  upwards  and  pin  it  to  the  arch  of  the  aorta  (see  Fig.  40).  The 
upper  part  of  the  anterior  wall  of  the  left  ventricle  and  the  commencement 
of  the  aorta  are  now  exposed,  and  the  dissector  should  note  three  bulgings 
at  the  commencement  of  the  aorta — the  three  aortic  sinuses.  One  of  the 
three  sinuses  lies  anteriorly,  and  the  right  coronary  artery  springs  from  it. 
The  other  two,  a  right  and  a  left,  lie  posteriorly,  and  the  left  coronary 
artery  springs  from  the  left  sinus. 

Make  a  transverse  incision  across  the  upper  end  of  the  left  ventricle,  a 
short  distance  below  the  base  of  the  anterior  aortic  sinus.  On  the  right 
side  extend  the  incision  into  the  upper  part  of  the  inter-ventricular  septum 
and  carry  it  downwards  and  anteriorly  in  the  septum  to  the  apex  of  the 
heart.  From  the  left  extremity  of  the  upper  transverse  incision  carry  an 
incision  downwards  and  anteriorly  through  the  left  lateral  border  of  the 
anterior  surface  of  the  left  ventricle,  parallel  with  the  incision  already  made 
in  the  septum,  towards  the  apex.     As  this  incision  is  made  pull  the  anterior 


THORACIC  CAVITY  79 

wall  of  the  left  ventricle  forwards  till  the  base  of  a  large  papillary  muscle 
which  springs  from  its  internal  surface  is  exposed  ;  carry  the  incision 
anterior  to  this  and  then  onwards  to  the  apex,  and  remove  the  anterior 
wall  of  the  left  ventricle  and  the  anterior  part  of  the  inter-ventricular 
septum.  The  cavity  of  the  left  ventricle  and  the  mitral  valve,  which  guards 
the  left  atrio-ventricular  orifice,  are  now  exposed  (Fig.  40). 

Ventriculus  Sinister. — The  cavity  of  the  left  ventricle  is 
longer  and  narrower  than  that  of  the  right  ventricle.  It 
reaches  to  the  apex,  and  when  exposed  from  the  front  it 
appears  to  be  of  conical  shape.  In  cross  section  it  has  a 
circular  or  broadly  oval  outline,  and  its  walls  are  very  much 
thicker  than  those  of  the  right  ventricle  (Fig.  37).  When 
the  interior  has  been  cleaned  with  the  aid  of  a  sponge  and 
forceps,  the  dissector  will  note  that  its  walls  are  covered  with 
a  dense  mesh-work  of  trabeculae  carneae,  which  are  finer  but 
much  more  numerous  than  those  met  with  in  the  right 
ventricle.  The  network  is  especially  complicated  at  the 
apex  and  on  the  inferior  wall  of  the  ventricle,  whilst  the 
surface  of  the  septum  and  the  upper  part  of  the  anterior  wall 
are,  comparatively  speaking,  smooth.  But  whilst  the  trabeculae 
carneae  in  the  left  ventricle  are  slighter  and  more  numerous 
than  those  in  the  right,  the  musculi  papillares,  on  the  other 
hand,  are  less  numerous  and  much  stronger;  indeed,  as  a 
general  rule  there  are  only  two  papillary  muscles  in  the  left 
ventricle,  an  anterior  and  an  inferior,  the  former  attached  to 
the  anterior  wall  and  the  latter  to  the  inferior  wall  of  the 
cavity.  The  chordae  tendineae  from  the  papillary  muscles 
pass  to  the  margins  and  to  the  ventricular  surfaces  of  the  two 
cusps  of  the  mitral  valve,  which  guards  the  left  atrio-ventricular 
orifice,  the  chordae  tendineae  from  each  papillary  muscle 
gaining  attachment  to  the  adjacent  margins  of  both  cusps. 

Dissection. — Detach  the  anterior  papillary  muscle  from  the  anterior 
wall  of  the  ventricle  and  note  that  its  chordse  tendineae  go  to  the  anterior 
and  left  margins  of  the  cusps  of  the  mitral  valve.  Introduce  the  blade  of 
a  scalpel  between  the  anterior  margins  of  the  cusps  and  carry  it  downwards 
between  the  groups  of  chordae  going  to  the  apex  of  the  papillary  muscle  ; 
then  split  the  papillary  muscle  from  its  apex  to  its  base  leaving  each  half 
connected  with  a  corresponding  group  of  chordae  tendineae.  The  cusps  of 
the  mitral  can  now  be  separated  from  each  other,  and  the  atrio-ventricular 
orifice  and  the  cavity  of  the  ventricle  can  be  more  completely  examined. 

The  Orifices  of  the  Left  Ventricle. — There  are  two  orifices 
of  the  left  ventricle — one  of  entrance,  the  left  atrio-ventricular 
orifice,  and  one  of  exit,  the  aortic  orifice. 

The    Left    Atrio  -  ventricular    Orifice, —  The    left    atrio- 


8o  THORAX 

ventricular  orifice  lies  in  the  lower  and  posterior  part  of  the 
ventricle  posterior  to  the  left  margin  of  the  sternum  at  the 
level  of  the  fourth  left  costal  cartilage.  It  is  somewhat  smaller 
than  the  right  atrio-ventricular  orifice  and  admits  the  tips  of 
two  fingers  only,  a  fact  which  will  be  better  appreciated  when 
the  orifice  is  examined  from  the  left  atrium  at  a  later  period. 
It  is  guarded  by  a  bicuspid  valve,  called  the  mitral  valve, 
which  prevents' regurgitation  of  blood  from  the  left  ventricle 
into  the  left  atrium. 

The  Mitral  Valve. — The  mitral  or  left  atrio-ventricular 
valve  consists  of  two  cusps,  a  large  anterior  and  a  small 
posterior.  Occasionally,  however,  as  on  the  right  side,  small 
additional  cusps  are  interposed  between  the  bases  of  the 
main  cusps.  The  bases  of  the  cusps  are  attached  to  a 
fibrous  ring  which  surrounds  the  atrio-ventricular  orifice  and 
their  apices  project  into  the  cavity  of  the  ventricle.  To  their 
apices,  margins,  and  ventricular  surfaces  are  attached  the 
chordae  tendinese  from  the  papillary  muscles,  which  hold  the 
margins  of  the  cusps  together  and  prevent  the  valve  being 
driven  backwards  into  the  atrium  during  the  contraction  of 
the  ventricle.  The  dissector  should  note,  however,  that  the 
chordae  tendinese  spread  less  over  the  ventricular  surface  of  the 
anterior  than  over  that  of  the  posterior  cusp,  and  he  should 
associate  this  fact  with  the  circumstance  that  blood  flows  over 
both  surfaces  of  the  large  anterior  cusp,  which  intervenes  between 
the  atrio-ventricular  and  the  aortic  orifices.  By  means  of 
this  large  anterior  cusp  of  the  mitral  valve  the  cavity  of  the 
ventricle,  which  has,  on  the  whole,  a  somewhat  conical  form, 
is  converted  into  a  bent  U-shaped  tube,  one  limb  of  the  tube 
lying  below  and  to  the  left,  and  the  other  anteriorly  and  to  the 
right.  The  blood  enters  the  ventricle  below  and  posteriorly 
through  the  atrio-ventricular  orifice.  It  runs  anteriorly  to- 
wards the  apex  of  the  cavity  along  the  inferior  surface  of 
the  anterior  cusp  of  the  mitral  valve,  then,  as  the  ventricle 
contracts,  it  is  driven  upwards,  anteriorly,  and  to  the  right,  to 
the  aortic  orifice,  along  the  anterior  surface  of  the  large 
anterior  cusp  of  the  mitral  valve.  The  portion  of  the  cavity 
of  the  left  ventricle  which  lies  directly  below  the  aortic 
orifice  is  known  as  the  aortic  vestibule  (Fig.  40).  Its  walls  con- 
sist mainly  of  fibrous  tissue  ;  therefore  they  remain  quiescent 
during  the  contraction  of  the  ventricle  and,  as  a  result,  the 
rapid  closure  of  the  aortic  valve  is  not  interfered  with  when 


THORACIC  CAVITY 


8i 


the  ventricular  contraction  ceases  and  the  elastic  reaction  of 
the  walls  of  the  aorta  tends  to  force  blood  back  into  the 
ventricle. 

The  aortic  orifice  lies   at   the  upper,   right,   and   anterior 
part  of  the  cavity,  posterior  to  the  left  margin  of  the  sternum  at 


Trachea- 
Innominate  artery 

Right  innonriinate  vein-i 
Left  innominate  vein 


Superior  vena  cava-- 


Ascending  aorta, - 


Upper  right  pulmonary'  vein 

Ria;ht  auricle 


Anterior  aortic  sinus 
Right  coronary'  artery- 


Moderator  band 

Anterior , 
papillary  muscle 


Tricuspid  orifice - 
Moderator  band-" 


Left  subclavian  artery 
Left  common  carotid  artery 
Left  internal  jugular  vein 

Left  subclavian  vein 
Arch  of  aorta 


Pulmonary'  artery'  turned 
upwards 


Left  pulmonary  artery 
Front  of  left  atrium 
Left  auricle 
Left  coronarj'  artery 

Left  posterior  aortic  sinus 
Aortic  vestibule 


Anterior  cusp  of  mitral 
valve 

Mitral  orifice 
Anterior  papillary 
muscle 


Posterior  papillajy 
muscle 


Interventricular 

septum 


Fig.  40. — Dissection  of  the  Heart  from  the  anterior  aspect. 

the  level  of  the  third  intercostal  space.  Its  left  and  inferior 
margin  is  separated  from  the  atrio-ventricular  orifice  by  the 
anterior  cusp  of  the  mitral  valve.  It  is  guarded  by  a  valve, 
the  aortic  valve,  which  prevents  regurgitation  from  the  aorta 
into  the  ventricle.  This  valve,  like  the  pulmonary  valve, 
consists  of  three  semilunar  cusps,  but  in  contradistinction  to 
VOL.  II — 6 


82 


THORAX 


the  pulmonary  valve,  one  of  the  cusps  is  placed  anteriorly  and 
the  other  two  posteriorly.  The  cusps  of  the  aortic  valve  are 
stronger  than  the  cusps  of  the  pulmonary  valve  described  on 
p.  75,  but  correspond  with  them  in  all  details  of  structure. 

Before  terminating  his  examination  of  the  left  ventricle 
the  dissector  should  note  that  the  muscular  wall  of  the 
cavity  is  thickest  a  short  distance  from  the  atrio-ventricular 

Opening  of  coronary  sinus     Interatrial  septum 

Right  atrium         ;  !      ^  .  ,       •  r.i. 

Musculi  pectinati      ....-SSSsK^    !         /       Part  of  right  sinus  of  the  aorta 


Lower  left 
,  pulmonary  vein 


Central 
fibrous  mass   7^. 
Fibrous  ring  of  /' 
tricuspid  orifice"? 
Inferior  cusp  of  |^ 
tricuspid  valve 
Medial  cusp  of 
tricuspid  valve  j 


Trabeculacarnea  -. 

Interventricular 
septum 


Wall  of  left 
'atrium 


Central 
fibrous  mass 


_,., ,       Pars  mem- 
^  "^fi"'"  branacea  septi 


lj{t-_/  Great  cardiac  vein 
*-  jT Fibrous  ring  of 
f-  mitral  orifice 
Posterior  cusp 
of  mitral  valve 
Anterior  cusp 
of  mitral  valve 

--  Wall  of  left  ventricle 


Fig.  41. — Section  of  the  Heart  showing  the  Interventricular  and  Inter- 
auricular  Septa  and  the  Fibrous  Rings  round  the  Orifices. 

orifice  and  thinnest  at  the  apex,  and  he  should  examine  the 
inter-ventricular  septum. 

TAe  Inter-ventricular  Septum. — The  inter-ventricular  septum 
is  a  musculo-membranous  partition  which  separates  the  left 
ventricle  not  only  from  the  right  ventricle,  but  also  from  the 
lower  part  of  the  right  auricle.  In  the  greater  part  of  its 
extent  the  septum  is  thick  and  muscular,  and  is  thickest  below 
and  anteriorly,  where  it  springs  from  the  lower  border  of  the 
heart  immediately  to  the  right  of  the  apex  and  opposite  the 


THORACIC  CAVITY  83 

cardiac  notch.  The  muscular  part  becomes  gradually  thinner 
as  it  passes  upwards  and  posteriorly  and,  a  short  distance 
from  the  atrio-ventricular  orifices,  it  terminates  in  a  fibrous 
membrane,  the  pars  inembranacea  sepfi,  which  connects  the 
muscular  part  of  the  septum  with  the  fibrous  rings  which 
surround  the  atrio-ventricular  orifices  and  the  orifices  of  the 
pulmonary  artery  and  the  aorta.  The  pars  membranacea  is 
the  thinnest  part  of  the  septum.  Occasionally  it  is  deficient 
in  whole  or  in  part,  and  in  such  cases  a  communication 
exists  between  the  two  ventricles,  and,  in  some  rare  cases, 
between  the  left  ventricle  and  the  right  auricle. 

The  pars  membranacea  was  exposed  from  the  right  side 
when  the  anterior  part  of  the  medial  cusp  of  the  tricuspid 
valve  was  removed  during  the  dissection  of  the  atrio-ventri- 
cular bundle  (see  p.  74). 

Finally  the  dissector  should  note  that  the  inter-ventricular 
septum  is  placed  obliquely,  so  that  its  anterior  border  lies  to 
the  left  and  its  inferior  border  to  the  right ;  and  that  its 
right  lateral  surface,  which  looks  anteriorly  and  to  the  right, 
bulges  towards  the  cavity  of  the  right  ventricle  (Fig.  37). 

The  Aorta. — The  aorta  is  the  great  arterial  trunk  of  the 
body.  It  commences  from  the  upper,  anterior  and  right 
portion  of  the  left  ventricle,  at  the  level  of  the  third  inter- 
costal spaces  and  posterior  to  the  left  margin  of  the  sternum. 
It  terminates  at  the  level  of  the  lower  border  of  the  fourth 
lumbar  vertebra,  to  the  left  of  the  median  plane,  where  it 
divides  into  the  right  and  left  common  iliac  arteries.  It  is 
described  as  consisting  of  three  main  parts:  (i)  the  ascend- 
ing part,  (2)  the  arch,  and  (3)  the  descending  part.  The 
descending  part  is  divided  into  {a)  thoracic  and  {b)  abdominal 
portions.  The  first  two  parts  and  the  thoracic  portion  of  the 
third  part  are  met  with  in  the  dissection  of  the  thorax. 

The  Ascending  Part  of  the  Aorta. — The  ascending  aorta 
commences  at  the  aortic  orifice  of  the  left  ventricle  and  runs 
upwards  to  the  right  and  slightly  anteriorly,  posterior  to  the 
first  piece  of  the  body  of  the  sternum,  to  the  level  of  the  sternal 
end  of  the  right  second  costal  cartilage,  where  it  becomes  the 
arch  of  the  aorta.  It  lies  in  the  middle  mediastinum,  is 
enclosed  in  the  fibrous  sac  of  the  pericardium,  and  is  en- 
sheathed  by  a  covering  of  the  serous  sac  which  is  common 
to  it  and  the  stem  of  the  pulmonary  artery.  The  lumen  of 
this  portion  of  the  aorta  is  not  of  uniform  diameter ;  on  the 
II — 6  a 


84 


THORAX 


contrary  it  presents  four  dilatations,  three  at  the  commence- 
ment, the  aortic  sinuses  (Valsalva),  and  one  along  the  right 
border,  the  great  sinus  of  the  aorta.  The  latter  is  merely  an 
indefinite  bulging  along  the  right  border  of  the  vessel. 

Relatiofis. — The    lower    part   of   the  ascending  aorta  lies 
posterior  to  the  upper  part  of  the  conus  arteriosus  and  the  lower 


Internal 


Pericardium 


ii!!^-_'J' Ascending  aorta 

r^^/t'^      Right  phrenic 


Left  phrenic 
nerve 


Thoracic  duct 


Vena  hemiazygos 
accessoria 


_Right  pulmon- 
ary artery 

Bifurcation  of 
trachea 
—  ^      Right  vagus 
Xc  \     nerve 

Bronchial  artery 

Vena  azygos 

Intercostal 
artery 

Sympathetic 
trunk 


Fig.  42. 


-Transverse  section  through  the  Mediastinal  Space  at  the 
level  of  the  fifth  dorsal  vertebra. 


part  of  the  stem  of  the  pulmonary  artery ;  but  the  upper  part 
is  in  direct  relation  with  the  anterior  wall  of  the  pericardium, 
which  separates  it  from  the  anterior  part  of  the  mediastinal 
surface  of  the  right  pleura  and  lung.  Posterior  to  the  ascend- 
ing aorta,  from  below  upwards,  are  the  left  atrium,  the  right 
pulmonary  artery  and  the  right  bronchus.  To  the  right  are 
the  right  auricle  below  and  the  superior  vena  cava  above  ;  and 


THORACIC  CAVITY  85 

to  the  left  lie  the  left  auricle  below,  and  the  upper  part  of  the 
stem  of  the  pulmonary  artery  above. 

Branches.  —  Only  two  branches  are  given  off  from  the 
ascending  part  of  the  aorta ;  they  are  the  right  and  left 
coronary  arteries.  The  right  springs  from  the  anterior 
aortic  sinus  and  the  left  from  the  left  posterior  sinus.  Their 
distribution  has  been  described  already  (p.  60). 

The  Superficial  Cardiac  Plexus. — Before  the  arch  of  the 
aorta  is  studied,  the  position,  connections  and  relations  of  the 
superficial  cardiac  plexus  should  be  defined.  It  lies  below 
the  arch  of  the  aorta,  above  the  bifurcation  of  the  stem  of  the 
pulmonary  artery,  and  between  the  ascending  aorta  on  the 
right  and  anteriorly,  and  the  ligamentum  arteriosum  to  the  left 
and  posteriorly.  The  positions  of  the  superior  cervical  cardiac 
branch  of  the  left  sympathetic  trunk,  and  the  inferior  cervical 
cardiac  branch  of  the  left  vagus,  on  the  left  side  of  the 
arch  of  the  aorta,  have  been  defined  already  (p.  33). 
Trace  these  nerves  to  the  plexus,  clear  away  the  areolar 
tissue  from  around  the  plexus,  and  trace  branches  posteriorly 
and  upwards  from  it  towards  the  deep  cardiac  plexus,  which 
lies  posterior  to  the  arch  of  the  aorta.  Other  branches  which 
spring  from  the  superficial  part  of  the  cardiac  plexus  descend 
along  the  pulmonary  artery  and  form  the  right  coronary 
plexus,  which  is  distributed  with  the  right  coronary  artery. 

The  Arch  of  the  Aorta. — The  aortic  arch  commences  at  the 
termination  of  the  ascending  part  of  the  aorta,  at  the  level  of 
the  second  costal  cartilage,  and  posterior  to  the  right  margin  of 
the  sternum,  from  which  it  is  separated  by  the  anterior  part 
of  the  mediastinal  portion  of  the  right  pleura  and  lung,  or 
by  the  remains  of  the  thymus  gland  (see  Fig.  43).  It  runs 
posteriorly,  to  the  left,  and  slightly  upwards,  through  the  middle 
mediastinum  and  round  the  left  margins  of  the  trachea  and 
oesophagus  (see  P'igs.  13  and  43),  to  the  level  of  the  lower 
border  of  the  left  side  of  the  fourth  thoracic  vertebra,  where  it 
becomes  continuous  with  the  descending  part  of  the  aorta.  It 
is  curved  in  both  the  vertical  and  the  horizontal  planes,  and  as 
it  passes  posteriorly  and  to  the  left  it  forms  a  convexity 
upwards,  and  also  a  convexity  which  is  directed  anteriorly  and 
to  the  left.  Its  lower  border  is  connected  with  the  left 
pulmonary  artery  by  the  ligamentum  arteriosum,  and  from  its 
upper  border  arise  the  three  great  vessels  which  supply  the 
head,  neck,  and  upper  extremities. 


86 


THORAX 


Relations. — Above,  the  left  innominate  vein  runs  along  its 
upper  border  immediately  anterior  to  the  origins  of  the  in- 
nominate artery,  the  left  common  carotid  artery  and  the  left 
subclavian  artery,  which  spring  from  its  upper  border ;  the  first 
arises  from  the  apex  of  the  convexity,  posterior  to  the  centre 


Internal 

mammary 

vessels 


Superior  vena 


erve 


CEsophagus 

Thoracic  duct 

Sympathetic 
trunk 


Phrenic  nerve  t^^W^A:^ 
Aortic  arch  ^»r^  J 


nerve  ^^ 
Left  superior  , 
intercostal  vein  ' 


Fig,  43. — Transverse  section  through  the  Superior  Mediastinum 
at  the  level  of  the  fourth  dorsal  vertebra. 

of  the  manubrium  sterni ;  the  second  arises  close  to,  and  some- 
times in  common  with  the  first,  whilst  the  origin  of  the 
subclavian  is  a  little  more  posterior  and  to  the  left,  separated 
by  a  distinct  interval  from  the  left  common  carotid  (Figs.  20  and 
24).  Be/ow  the  arch  lie  (i)  the  bifurcation  of  the  pulmonary 
artery  and  portions  of  its  right  and  left  branches ;  (2)  the  liga- 


THORACIC  CAVITY  87 

mentum  arteriosum,  which  connects  the  left  pulmonary  artery 
with  the  arch ;  (3)  the  superficial  part  of  the  cardiac  plexus 
immediately  to  the  right  of  the  ligamentum  arteriosum  ;  (4) 
the  left  recurrent  nerve  on  the  left  side  of  the  Hgament ;  and  (5) 
still  further  to  the  left,  the  left  bronchus  passes  beneath  the 
arch  on  its  way  to  the  hilus  of  the  left  lung.  To  the  right  of  the 
arch  are  the  trachea,  the  oesophagus,  the  left  recurrent  nerve, 
and  the  thoracic  duct.  The  nerve  lies  in  the  angle  between 
the  oesophagus  and  the  trachea,  and  the  thoracic  duct  is  pos- 
terior to  and  to  the  left  of  the  oesophagus  (Fig.  43).  The  left 
side  of  the  ar^h  is  overlapped  by  the  posterior  part  of  the  media- 
stinal surface  of  the  left  pleura  and  lung,  but  intervening 
between  the  pleura  and  the  arch  are  (1)  the  left  phrenic  nerve, 
(2)  the  inferior  cervical  cardiac  branch  of  the  left  vagus,  (3) 
the  superior  cervical  cardiac  branch  of  the  left  sympathetic, 
(4)  the  left  vagus,  and  (5)  the  left  superior  intercostal  vein. 
The  vein  passes  upwards  and  anteriorly,  lying  to  the  left  of 
the  vagus  and  the  cardiac  nerves,  and  to  the  right  of  the 
phrenic  nerve  (Fig.  13). 

Dissection.— X>vj'\^&  the  right  coronary  artery  close  to  its  origin.  ^  Cut 
through  the  anterior  wall  of  the  ascending  part  of  the  aorta  on  each  side  of 
the  anterior  aortic  sinus  ;  extend  the  incisions  upwards  to  the  commencement 
of  the  aortic  arch,  and  examine  the  aortic  valve.  Note  that  it  is  formed  by 
three  semilunar  cusps  which  are  much  stronger  than  the  semilunar  cusps  of 
the  pulmonary  valve  (p.  75),  but  are  exactly  similar  in  structure  and 
attachments.  Note  further  that  one  cusp  lies  anteriorly,  and  the  other  two 
posteriorly.  Examine  the  aortic  sinuses  and  note  that  the  right  coronary 
artery  springs  from  the  anterior  sinus,  and  the  left  coronary  from  the  left 
posterior  sinus.  Note  further  that  the  orifices  of  the  coronary  arteries,  as  a 
rule,  lie  immediately  above  the  level  of  the  upper  margins  of  the  semilunar 
cusps.  Replace  the  stem  of  the  pulmonary  artery  in  position,  and  note  the 
relative  positions  of  the  pulmonary,  aortic,  and  atrio-ventricular  orifices. 

Topography  of  the  Great  Orifices  of  the  Heart. — Replace 
the  sternum  in  position  and  note  the  relations  of  the  cardiac 
orifices  to  that  bone.  The  pulmonary  orifice  is  highest.  It 
lies  to  the  left  of  the  margin  of  the  sternum  at  the  level  of  the 
third  costal  cartilage.  The  aortic  orifice  is  a  little  lower,  and 
more  to  the  right,  posterior  to  the  left  margin  of  the  sternum, 
at  the  level  of  the  third  left  intercostal  space.  Below  the  aortic 
orifice  is  the  left  atrio-ventricular  orifice,  posterior  to  the  left 
margin  of  the  sternum  at  the  level  of  the  left  fourth  costal 
cartilage.  Still  lower  and  more  to  the  right  is  the  right  atrio- 
ventricular orifice,  posterior  to  the  centre  of  the  sternum  at  the 
level  of  the  fourth  intercostal  spaces  (Fig.  44). 


88 


THORAX 


Dissection. — Divide  the  phrenic  nerves  immediately  above  the  diaphragm ; 
then,  with  the  handle  and  the  edge  of  the  scalpel,  detach  the  lower  part 
of  the  pericardium  from  the  diaphragm.  The  attachment  of  the  peri- 
cardium to  the  muscular  part  of  the  diaphragm  is  not  close,  and  can 
easily  be  broken  down.  The  attachment  to  the  central  tendon  is  much 
more  firm  and,  as  the  median  plane  is  approached,  the  aid  of  the  edge  of 
the  knife  will  probably  be  necessary  before  a  separation  can  be  effected. 


Fig.  44. — The  relations  of  the  Heart  and  of  its  Orifices  to  the  Anterior 
Thoracic  Wall.     (Young  and  Robinson. ) 


I  to  VII.  Costal  cartilages. 
A.  Aorta. 
Ao.  Aortic  orifice. 

C.  Clavicle. 
LA.  Left  atrium. 
LV.  Left  ventricle. 


M.  Mitral  orifice. 

P.  Pulmonary  orifice. 

RA.  Right  atrium. 

RV.  Right  ventricle. 

SVc.  Superior  vena  cava. 

T.  Tricuspid  orifice. 


Divide  the  right  innominate  vein  and  the  right  phrenic  nerve,  immediately 
above  the  upper  end  of  the  superior  vena  cava,  and  as  the  division  is  made 
take  care  not  to  injure  the  right  vagus  posterior  to  the  vein.  Then  divide 
the  vena  azygos  just  posterior  to  its  entrance  into  the  superior  vena  cava. 
Cut  the  inferior  thyreoid  veins,  the  innominate  artery,  and  the  left  common 
carotid  artery,  immediately  above  the  upper  border  of  the  left  innominate 
vein,  and  then  divide  the  left  innominate  vein,  in  the  interval  between  the 
left  common  carotid  and  the  left  subclavian  arteries.     Cut  the  left  phrenic 


THORACIC  CAVITY  89 

nerve,  the  superior  cardiac  branch  of  the  left  sympathetic,  and  the  inferior 
cervical  cardiac  branch  of  the  left  vagus,  immediately  above  the  upper 
border  of  the  aortic  arch.  Next  divide  the  aortic  arch.  Enter  the  knife  at 
the  upper  border  of  the  arch,  between  the  left  common  carotid  and  left 
subclavian  arteries  and  anterior  to  the  left  vagus  and  the  left  recurrent 
nerve,  and  cut  from  above  downwards,  completing  the  division  of  the 
arch  at  the  lower  border,  immediately  to  the  left  of  the  upper  end  of 
the  ligamentum  arteriosum.  The  left  superior  intercostal  vein  will  be 
divided  at  the  same  time,  but  care  must  be  taken  not  to  injure  the  left 
recurrent  nerve,  which  is  curving  round  the  arch  from  the  front  to  the 
back.  When  the  incisions  are  completed,  pull  the  anterior  part  of  the 
aortic  arch,  with  the  superior  vena  cava  and  the  lower  parts  of  the  innomi- 
nate veins,  anteriorly,  and  separate  them  from  the  lower  part  of  the 
trachea  and  from  the  bronchi.  As  the  separation  proceeds,  keep  the  edge 
of  the  knife  turned  towards  the  aortic  arch,  to  avoid  injury  to  the  deep  part 
of  the  cardiac  plexus,  which  lies  anterior  to  the  bifurcation  of  the  trachea. 
When  the  lower  border  of  the  arch  is  reached,  the  twigs  which  connect  the 
superficial  with  the  right  half  of  the  deep  part  of  the  cardiac  plexus  will 
be  exposed,  and  must  be  divided.  When  this  has  been  done  detach  the 
posterior  surface  of  the  pericardium  from  the  front  of  the  oesophagus  and 
the  descending  aorta,  taking  care  to  avoid  injury  to  the  plexus  formed  by 
the  vagi  nerves  on  the  anterior  aspect  of  the  oesophagus.  As  soon  as  the 
separation  is  completed,  the  heart,  with  the  remains  of  the  pericardium  and 
the  lower  parts  of  the  phrenic  nerves,  can  be  removed  from  the  thorax,  and 
the  investigation  of  the  left  atrium  and  the  structure  of  the  heart  can 
be  proceeded  with  ;  but,  before  this  is  done,  the  dissector  should  note  that 
the  posterior  wall  of  the  pericardium  intervenes  between  the  posterior  wall 
of  the  left  atrium  and  the  anterior  surfaces  of  the  oesophagus  and  the 
descending  part  of  the  aorta,  as  the  latter  structures  lie  anterior  to  the 
middle  four  thoracic  vertebrse  (Fig.  21). 

After  the  heart  and  the  roots  of  the  great  vessels  have  been  removed  from 
the  thorax,  fasten  the  left  vagus  and  the  recurrent  nerve  to  the  part  of  the 
arch  left  in  situ  by  one  or  two  points  of  suture  ;  then  cut  away  the  remains 
of  the  pericardium  from  the  heart,  leaving  only  those  portions  of  it  which 
mark  the  lines  of  reflection  of  the  parietal  to  the  visceral  portions  of  the 
serous  sac.  Note,  as  the  posterior  wall  of  the  pericardium  is  removed,  that 
it  forms  the  posterior  boundary  of  the  oblique  sinus  (p.  21). 

The  Left  Atrium. — The  left  atrium,  like  the  right,  is 
separable  into  two  parts — a  larger  main  portion,  the  atrium 
proper  or  body ;  and  a  long  narrow  prolongation,  the  auricle 
(O.T.  auricular  appendage),  which  runs  from  the  left  margin 
of  the  body  anteriorly  and  to  the  right.  The  four  pulmonary 
veins,  two  on  each  side,  open  into  the  left  atrium.  They  enter 
close  to  the  upper  ends  of  the  lateral  borders  of  the  posterior 
surface,  and  not  uncommonly  the  right  or  the  left  pair  may 
fuse  into  a  common  trunk  at  the  point  of  entrance. 

It  has  been  noted  previously  that  the  left  atrium  forms 
the  greater  part  of  the  base  of  the  heart,  a  small  part  of  the 
anterior  or  sterno-costal  surface,  and  a  still  smaller  part  of 
the  left  border.  The  only  part  which  can  be  seen  from  the 
front,  when  the  heart  is  in  situ,  is  the  apical  portion   of  the 


90 


THORAX 


auricle  (appendage),  for  the  portion  which  enters  into  the 
formation  of  the  sterno-costal  surface  is  hidden  by  the  roots 
of  the  aorta  and  the  pulmonary  artery  (Fig.  35). 

The  posterior  wall  of  the  left  atrium  is  of  quadrangular 
outUne.  Along  its  superior  border  lie  the  pulmonary  arteries. 
It  is  bounded  inferiorly  by  the  posterior  part  of  the  coronary 


Left  common  carotid 

Aorta 
Ligamentiim  arteriosum 

Left  pulmonary  artery- 


Reflection  of  serous 
pericardium 


Left 
pulmonary 


Left  atrium 

Oblique  vein 
Left  ventricle. 

Coronary  sulcus 

(O.T.  Auriculo 

ventricular  groove; 

Coronary  sinu; 

Inferior  surface 
ventricular 

of  heart 


-  Innominate  artery 
Right  innominate 
vein 


Vena  azygos 

Superior 
\  ena  cava 


Right  pulmonary 
irtery 

Right  pulmonary 


Sulcus 
terminalis 

Right 
pulmonary  vein 


Interatrial 
sulcus 

Right  atrium 


Inferior  vena 
cava 


Fig.  45. — Posterior  or  Basal  Aspect  of  a  Heart  hardened  in  situ  by 
formalin  injection. 

sulcus,  in  which  lies  the  coronary  sinus,  and  on  the  right  by 
an  indistinct  inter-atrial  sulcus,  which  indicates  the  position 
of  the  posterior  border  of  the  inter-atrial  septum.  Descending 
obliquely  across  the  posterior  wall  of  the  left  atrium,  from 
the  lower  border  of  the  left  inferior  pulmonary  vein,  down- 
wards and  to  the  right  to  the  coronary  sinus,  is  the  oblique 
vein  (Marshall),   which  is  the   remains   of   the    left   duct   of 


THORACIC  CAVITY 


91 


Cuvier  of  the  foetus.     Occasionally  it  becomes  the  lower  end 
of  a  left  superior  vena  cava. 

Dissection. — Open  the  left  atrium  by  three  incisions — one  horizontal  and 
two  vertical.  The  horizontal  incision  must  run  from  side  to  side  along  the 
lower  border  of  the  atrium,  immediately  above  the  coronary  sulcus  ;  and 
the  vertical  incisions  must  ascend  from  the  extremities  of  the  horizontal  to 
the  upper  border  of  the  posterior  surface,  each  passing  to  the  medial  side 
of  the  terminations  of  the  corresponding  pulmonary  veins.  When  the 
incisions  have  been  made  the  posterior  wall  of  the  atrium  must  be  turned 
upwards  whilst  the  cavity  is  being  examined. 


Aorta 


Left  pulmonary  veins 


Pulmonary  artery 


Left  auricle 
(O.T.  appendix 


Mitral  _    _  /  ' 

orifice  '^       ^ 


,'  Right  pul- 
Imonary  veins 


sition  of  fossa 
ovalis  in  right  atrium 


Coronary  sinus 

Fig.  4^. — The  Left  Atrium  opened  from  behind.     The  greater  part  of 
the  posterior  wall  has  been  thrown  upwards. 

The  inner  surface- of  the  wall  of  the  left  atrium  is  smooth 
and  generally  devoid  of  muscular  bundles,  but  the  inner 
surface  of  the  wall  of  its  auricle  (O.T.  auricular  appendage)  is 
covered  with  musculi  pectinati,  a  fact  which  can  be  demon- 
strated by  carrying  an  incision  anteriorly  into  it.  As  this 
incision  is  made,  the  dissectors  should  note  that,  in  a  formalin 
hardened  heart,  a  strong  muscular  ridge  descends  along  the 
left  border  of  the  cavity  anterior  to  the  orifices  of  the  left 
pulmonary  veins,  entirely  concealing  them  from  view  when  the 
cavity  is  examined  from  the  front. 

On  the  right  or  septal  wall  of  the  left  atrium  the  position 


92  THORAX 

of  the  valve  of  the  foramen  ovale  is  marked  by  one  or  more 
small  semilunar  depressions  situated  between  slender  muscular 
ridges.  The  portion  of  the  septal  wall  which  lies  below  and 
posterior  to  these  depressions  forms  the  floor  of  the  fossa 
ovalis,  and  is  the  remains  of  the  valve  of  the  foramen  ovale  of 
the  foetus. 

The  Orifices  of  the  Left  Atrium. — The  orifices  of  the  left 
atrium  are  the  openings  of  the  four  J)ul7?ionary  veins,  which 
convey  to  it  the  oxygenated  blood  from  the  lungs ;  a  number 
of  minute  openings  which  are  the  mouths  of  the  vencs  cordis 
minimcB ;  and  the  left  atrio-ventricular  orifice  through  which 
blood  passes  from  the  left  atrium  to  the  left  ventricle. 

The  openings  of  the  pulmonary  veins  are  situated  in  the 
posterior  wall,  nearer  the  upper  than  the  lower  part,  and  close 
to  the  lateral  borders,  two  on  each  side.  They  are  entirely 
devoid  of  valves.  The  orifices  of  the  venae  cordis  minimae, 
which  are  scattered  irregularly,  are  also  valveless ;  but  the  left 
atrio-ventricular  orifice,  which  lies  in  the  lower  part  of  the 
anterior  wall  of  the  atrium,  is  guarded  by  a  bicuspid  valve,  the 
mitral  valve,  which  has  been  described  already  (p.  79).  This 
orifice  is  smaller  than  the  corresponding  orifice  on  the  right 
side,  and  admits  the  tips  of  two  fingers  only. 

The  Structure  of  the  Walls  of  the  Heart. — The  last  step  in  the  dissection 
of  the  heart  consists  in  the  examination  of  the  structure  of  its  walls.  On 
the  outside  the  walls  are  covered  with  the  epicardium,  which  is  the  visceral 
part  of  the  serous  pericardium  ;  and  on  the  inside  they  are  lined  with  the 
smooth  and  glistening  endocardmm,  which  plays  a  large  part  in  the 
formation  of  the  flaps  of  the  valves,  and  is  continuous,  through  the 
orifices,  with  the  inner  coats  of  the  arteries  and  veins.  Between  the 
epicardium  and  the  endocardium  lies  the  muscular  tissue  of  the  heart, 
which  is  termed  the  myocardium.  The  muscular  fibres  of  the  myo- 
cardium are  disposed  in  layers,  in  each  of  which  the  fibres  take  a  special 
direction. 

The  arrangement  of  the  various  layers  of  the  myocardium  cannot  be 
displayed  in  an  ordinary  dissecting-room  heart,  in  which  the  continuity  of 
the  fibres  has  been  destroyed  by  the  incisions  made  to  display  the  cavities, 
but  the  arrangement  of  the  layers  is  practically  the  same  in  the  hearts  of 
all  mammals.  Therefore,  for  the  purpose  of  studying  the  layers,  the 
dissector  should  obtain  a  sheep's  heart.  This  should  be  filled  with  a 
paste  made  of  flour  and  water  ;  then  it  should  be  boiled  for  a  quarter  of  an 
hour.  The  boiling  expands  the  paste,  softens  the  connective  tissue,  and 
hardens  the  muscular  fibres.  After  the  boihng  is  finished  the  heart  should 
be  placed  for  a  time  in  cold  water.  After  it  has  cooled,  first  the  epicardium 
and  then  the  muscular  fibres  should  be  gradually  torn  off. 

The  atrial  fibres  are  difficult  to  dissect.  They  consist  of  three  groups  : 
(i)  A  superficial  group  running  more  or  less  transversely  and  common  to 
both  atria.  They  are  best  marked  near  the  coronary  sulcus.  (2)  A  deep 
group  special  to  each  auricle.     The  extremities  of  these  fibres  are  connected 


THORACIC  CAVITY  93 

with  the  fibrous  atrio-ventricular  rings,  and  they  pass  over  the  auricles  from 
front  to  back.  (3)  The  third  group  consists  of  sets  of  annular  fibres 
surrounding  the  orifices  of  the  veins  which  open  into  the  atria. 

The  fibres  of  the  ventricles  are  more  easily  dissected.  They  consist, 
for  the  main  part,  of  two  groups — the  superficial  and  the  deep.  The  fibres 
of  each  set  are  common  to  both  ventricles,  and  the  dissectors  should  note 
the  remarkable  spiral  or  whorled  arrangement  of  the  superficial  fibres 
which  occurs  at  the  apex,  where  they  pass  into  the  deeper  parts  of  the  wall. 

The  superficial  fibres  spring  mainly  from  the  fibrous  atrio-ventricular 
rings.  Those  which  are  attached  to  the  right  ring  turn  inwards  at  the 
apex  and  become  continuous  with  the  papillary  muscles  of  the  left  ventricle, 
whilst  the  fibres  which  spring  from  the  left  ring  pass  in  the  same  way  to 
the  papillary  muscles  of  the  right  ventricle.  The  deeper  fibres  form  an 
(y^-shaped  layer,  one  loop  of  the  CO  surrounding  the  right  and  the  other  the 
left  ventricle. 

The  fibrous  rings  of  the  atrio-ventricular  orifices  intei^vene  between  the 
atrial  and  the  ventricular  muscle  fibres,  but  the  two  groups  are  brought 
into  association  with  each  other  by  the  atrio-ventricular  bundle  described 
on  p.  74.  It  has  been  assumed  that  the  impulses  which  regulated  the 
movements  of  the  ventricles  were  conveyed  to  them  from  the  atria  by 
the  fibres  of  this  bundle,  but  it  has  been  shown  recently  that  numerous 
nerve  fibrils  are  intimately  intermingled  with  the  fibres  of  the  atrio- 
ventricular bundle.  It  is  possible,  therefore,  that  the  connection  between 
the  atria  and  the  ventricles  is  neuro-muscular. 

The  Action  of  the  Heart. — The  differences  between  the  various  parts  of 
the  heart,  i.e.  the  thinness  of  the  walls  of  the  atria  as  contrasted  with  the 
thickness  of  the  walls  of  the  ventricles,  and  the  greater  thickness  of  the 
walls  of  the  left  as  contrasted  with  those  of  the  right  ventricle,  are  associated 
with  the  functions  of  the  various  chambers,  and  with  the  action  which  the 
heart  plays  in  the  maintenance  of  the  circulation  of  the  blood.  The  heart 
is  a  muscular  pump,  provided  with  receiving  and  ejecting  chambers.  It 
has  three  phases  of  action  :  (i)  a  period  of  atrial  contraction  ;  (2)  a  period 
of  ventricular  contraction,  which  immediately  succeeds  the  atrial  con- 
traction ;  (3)  a  period  of  diastole  or  rest. 

During  the  period  of  diastole  or  rest  the  chambers,  previously  con- 
tracted, dilate,  as  the  muscular  fibres  of  the  heart  relax.  The  dilatation  is 
aided  by  the  respiratory  movements  of  the  thorax.  As  the  dilatation  pro- 
gresses blood  flows  into  the  right  atrium  from  the  superior  vena  cava,  the 
inferior  vena  cava,  and  the  coronary  sinus  ;  and  into  the  left  atrium  through 
the  four  pulmonary  veins.  The  atrial  contraction  commences  with  the 
contraction  of  the  circular  fibres  which  surround  the  mouths  of  the  veins 
entering  the  atria,  and  thus  the  blood  is  prevented  from  passing  back 
into  the  veins.  As  the  contraction  extends  to  the  general  fibres  of  the  atria 
the  blood  is  forced  onwards  into  the  ventricles,  which  become  distended. 
Then  the  ventricular  contraction  commences,  the  atrio-ventricular  valves 
close,  and,  as  the  contraction  proceeds,  the  blood  is  driven  out  of  the 
ventricles  through  the  arterial  orifices,  that  in  the  right  ventricle  being 
ejected  into  the  pulmonary  artery,  and  that  in  the  left  ventricle  into  the  aorta. 

^Yhen  the  ventricular  contraction  is  completed  the  period  of  diastole 
commences  ;  and,  as  long  as  the  heart  remains  alive,  the  cycle  is  repeated. 

The  work  of  the  atria  is  merely  to  force  the  blood  through  the  widely 
open  atrio-ventricular  orifices  into  the  ventricles  and  to  expand  the  dilating 
walls  of  the  ventricles.  For  this  purpose  no  great  force  is  required,  there- 
fore the  walls  of  the  atria  are  thin.  The  work  of  the  ventricles  is  much 
more  severe,  therefore  their  walls  are  thicker,  but  the  right  ventricle  has 
only  to  exert  sufficient  force  to  drive  the  blood  through  the  lungs  to  the  left 


94 


THORAX 


auricle,  that  is,  through  a  comparatively  short  distance  and  against  a  com- 
paratively small  resistance  ;  therefore  its  walls  are  thin  as  compared  with 
the  walls  of  the  left  ventricle,  which  has  to  be  sufficiently  strong  to  force 
the  blood  through  the  whole  of  the  trunk,  the  head  and  neck,  and  the  upper 
and  lower  limbs. 

The  Topography  of  the  Heart. — Before  proceeding  to  the 
study, of  the  trachea,  the  dissectors  should  replace  the  heart 
in  position  and  revise  their  knowledge  of  its  relations  to  the 
surface.  Its  position  can  be  indicated  on  the  anterior  wall 
of  the  thorax  by  the  following  four  lines: — (i)  A  line  com- 
mencing at  the  lower  border  of  the  second  left  costal 
cartilage,  half  an  inch  from  the  left  border  of  the  sternum, 
and  ending  at  the  upper  border  of  the  third  right  costal 
cartilage,  half  an  inch  from  the  right  border  of  the  sternum. 
This  line  indicates  the  position  of  the  upper  border  of  the 
heart,  which  is  formed  by  the  atria.  (2)  A  line  from 
the  upper  border  of  the  third  right  costal  cartilage  to  the 
sixth  right  costal  cartilage.  This  line  should  commence 
and  end  half  an  inch  from  the  border  of  the  sternum,  and 
should  be  slightly  convex  to  the  right.  It  indicates  the 
right  border  of  the  heart,  which  is  formed  by  the  right  atrium 
alone.  (3)  A  line  from  the  sixth  right  costal  cartilage  to  the 
apex,  which  lies  behind  the  fifth  left  intercostal  space  three 
and  a  half  inches  from  the  median  plane.  This  line  marks 
the  position  of  the  lower  border  of  the  sterno-costal  surface, 
which  is  formed,  in  the  greater  part  of  its  extent,  by  the 
right  ventricle,  the  left  ventricle  entering  into  its  constitu- 
tion only  in  the  region  of  the  apex.  (4)  A  line  from  the 
apex  to  the  lower  border  of  the  second  left  costal  cartilage. 
This  line  should  be  convex  upwards  and  to  the  left ;  the 
point  of  greatest  convexity  should  coincide  with  the  lower 
border  of  the  fourth  left  costal  arch,  and  the  upper  extremity 
should  be  situated  half  an  inch  from  the  left  margin  of  the 
sternum.  It  marks  the  position  of  the  left  border  of  the 
heart,  which  is  formed  in  four-fifths  of  its  length  by  the  left 
ventricle  and  in  the  remaining  fifth  by  the  left  atrium. 

A  line  from  the  upper  border  of  the  sternal  end  of  the 
third  left  costal  cartilage  to  the  lower  border  of  the  sternal 
end  of  the  sixth  right  cartilage  indicates  the  anterior  part 
of  the  coronary  sulcus.  The  points  indicating  the  positions 
of  the  arterial  and  atrio-ventricular  orifices  must  be  placed 
below  and  to  the  left  of  the  line  of  the  coronary  sulcus  in 
the  following  order  from  above  downwards ;  pulmonary  orifice^ 


THORACIC  CAVITY 


95 


aortic  orifice^  mitral  orifice^  tricuspid  orifice.  The  centre  of  the 
pulmonary  orifice  is  posterior  to  the  third  left  costal  cartilage 
at  the  margin  of  the  sternum.  The  aortic  orifice  lies 
posterior  to  the  left  half  of  the  sternum  opposite  the  third  inter- 


Right  common  carotid  artery 
Orifice  of  right  internal  jugular  vein     \ 
Right  subclavian  artery 
Right  subclavian  vein 


Innominate  artery 


Left  common  carotid  artery 
I  End  of  left  internal  jugular  \'ein 
Left  subclavian  artery 

Left  subclavian  vein 


Right  superior  inter- 
costal vein 

Vena  azygos 


Eparterial  branch  of 
right  bronchus 

Stem  of  right  bronchus 

Right  vagus  nerve 

Right  intercostal  vein 

Right  aortic  intercostal 

artery 

Right  great  splanchnic 
nerve 

Right  sympathetic 
trunk 

Inferior  vena  cava 


Trachea 
Termination  of 
aortic  arch 


Left  bronchus 
Left  vagus  nerve 


Descending  thoracic  aorta 
(Esophageal  plexus 


Fig.  47. — Dissection  of  tlie  Posterior  Mediastinum  and  the  posterior  part 
of  the  Superior  Mediastinum  from  the  anterior  aspect. 

costal  spaces.  The  mitral  orifice  is  posterior  to  the  left  border 
of  the  sternum  at  the  level  of  the  fourth  left  costal  cartilage ; 
and  the  centre  of  the  tricuspid  orifice  is  posterior  to  the  middle 
of  the  sternum  at  the  level  of  the  fourth  intercostal  spaces. 

The    Thoracic    Portion    of  the    Trachea. — The    thoracic 
portion   of  the  trachea,  like   the  cervical  portion,  is  a  wide 


96 


THORAX 


tube  kept  constantly  patent  by  a  series  of  cartilaginous  rings 
embedded  in  its  walls.  Posteriorly  the  rings  are  deficient 
and  in  consequence  the  tube  is  flattened  behind  (Fig.  43). 
It  enters  the  thorax  at  the  upper  aperture,  posterior  to  the 
upper  border  of  the  manubrium,  and  it  terminates,  at  the  level 
of  the  lower  border  of  the  manubrium  and  the  upper  border 
of  the  fifth  thoracic  vertebra,  by  dividing  into  a  right  and  a 
left  bronchus.     It  lies,  therefore,  in  the  superior  mediastinum. 


Trachea 


Right 

bronchus 

Eparterial 

branch 


First  ventral 

branch 

First  dorsal 

branch 

First  ventral 
branch 

Stem  of 
bronchus 


Left  bronchus 

First  ventral 
branch 

First  dorsal 
branch 


Stem  of 
bronchus 


Fig.  48. — Drawing  of  a  Stereoscopic  Skiagraph  of  the  Trachea  and  Bronchi 
injected  with  starch  and  red  lead. 

and  its  median  axis  is  in  the  median  plane,  except  at  the 
lower  end  where  it  deviates  slightly  to  the  right. 

Relations. — Posteriorly^  it  is  in  contact  with  the  oesophagus, 
which  separates  it  from  the  vertebral  column ;  and  in  the 
angle  between  its  left  border  and  the  anterior  surface  of 
the  oesophagus  is  the  left  recurrent  nerve  (Fig.  43). 

Anteriorly^  it  is  in  relation  below  with  the  arch  of  the 
aorta,  the  deep  part  of  the  cardiac  plexus  intervening;  and 
at  a  higher  level  with  the  innominate  and  left  common 
carotid  arteries,  the  left  innominate  vein  and  the  inferior 
thyreoid   veins.      More    superficially  lie   the  remains  of  the 


THORACIC  CAVITY 


97 


Thyreoid  cartilage 


Crico-thyreoid 
ligament 

Cricoid  cartilage 

Part  of  trachea 
covered  by  isthmus 
of  thyreoid  gland 


Common  carotid 
artery 

Left  subclavian 
artery 


thymus,   and  still    more    superficially   the    manubrium  sterni 
with  the  origins  of  the  attached  muscles. 

On  the  rights  it  is  in  relation  with  the  upper  part  of  the 
mediastinal  surface  of  the  right  pleura  and  lung  (Fig.  43), 
the  right  vagus  nerve,  and 
the  arch  of  the  azygos 
vein  (Fig.  12).  It  is  also 
in  relation,  on  its  right 
side,  near  its  lower  end 
and  more  anteriorly,  with 
the  superior  vena  cava, 
and  at  a  higher  level  with 
the  innominate  artery. 

Its  left  lateral  relations 
are  the  arch  of  the  aorta 
below  and  the  left  sub- 
clavian and  left  common 
carotid  arteries  above. 

The    Bronchi.  —  Each 
bronchus    passes     down- 
wards  and   laterally  first 
to  the  hilus  of  the  corre- 
sponding lung  and  thence 
downwards    in    the   sub- 
stance of  the  lung  to  its 
lower  end.     It  can, 
therefore,  be  divided 
into     an     extra-pul- 
monary and  an  intra- 
pulmonary    portion. 
The  extra-pulmonary 
part,  like  the  trachea, 
is  kept  permanently 
open  bythe  presence 
of  cartilaginous  rings 
in  its  walls ;  and  as 
the    rings    are   defi 


-Aortic  arch 


Left  bronchus 
Left  pulmonary 
artery 

First  ventral 
branch  of 
left  bronchus 


Eparterial  bianch  of 

right  bronchus 
Hyparterial  branch  of 
I      right  bronchus 
Right  pulmonary  artery 

Fig.  49. — The  Trachea  and  Bronchi.      The  dotted 
Hne  gives  the  outline  of  the  thyreoid  gland. 


cient  posteriorly,  the  extra-pulmonary  part  of  each  bronchus 
presents  a  flattened  posterior  surface  similar  to  that  of  the 
trachea.  The  lumina  of  the  intra-pulmonary  parts  of  the 
bronchi  are  kept  patent  by  cartilaginous  plates  which  are 
irregularly  distributed  in  the  substance  of  the  walls. 

VOL.  II — 7 


98  THORAX 

Relations  of  the  Extra-puhjionary  Part  of  the  Right 
Bronchus. — The  right  bronchus  is  much  more  vertical  than 
the  left  (Fig.  48),  and,  as  the  ridge  which  separates  the  orifices 
of  the  two  bronchi  at  their  origins,  lies  to  the  left  of  the 
median  line  of  the  trachea,  the  right  bronchus  is  the 
direct  continuation  of  the  trachea,  and  foreign  bodies,  which 
have  entered  the  windpipe,  pass  more  frequently  into  it  than 
into  the  left  bronchus.  It  passes  downwards  and  laterally 
from  the  upper  border  of  the  fifth  thoracic  vertebra  to  the 
level  of  the  upper  part  of  the  sixth  thoracic  vertebra,  where 
it  enters  the  hilus.  Anterior  to  the  extra-pulmonary  part  of 
the  right  bronchus  are  the  ascending  part  of  the  aorta,  the 
lower  part  of  the  superior  vena  cava,  and  the  right  pulmonary 
artery.  Above  it  is  the  arch  of  the  azygos  vein  ;  d^wd, posterior  to 
it  are  the  azygos  vein,  the  posterior  pulmonary  plexus,  and  the 
right  bronchial  artery.  This  part  of  the  right  bronchus  gives 
off  one  branch,  which  arises  close  to  the  hilus  and  is  called 
the  eparterial  bronchus,  because  it  originates  immediately 
above  the  point  where  the  right  pulmonary  artery  crosses 
anterior  to  the  stem  bronchus. 

Relations  of  the  Extra-pulmonary  Part  of  the  Left  Bronchus. 
— The  extra-pulmonary  part  of  the  left  bronchus  commences 
and  ends  at  the  same  level  as  the  corresponding  part  of  the 
right  bronchus,  but  it  has  further  to  go,  because  the  hilus  of 
the  left  lung  is  further  from  the  median  plane  than  the 
hilus  of  the  right  lung ;  therefore  it  is  longer  and  less  vertical 
than  the  right  bronchus.      It  gives  off  no  branches. 

Anterior  to  it  are  the  left  pulmonary  artery,  and  the  upper 
and  left  part  of  the  pericardial  sac  which  separates  the 
bronchus  from  the  left  auricle.  Above  it  is  the  arch  of  the 
aorta,  and  posterior  to  it  are  the  descending  aorta,  the  posterior 
pulmonary  plexus,  the  left  bronchial  arteries,  and  the  oeso- 
phagus. 

Dissection. — The  intra- pulmonary  parts  of  the  bronchi  and  the  intra- 
pulmonary  parts  of  the  pulmonary  arteries  and  veins  should  now.  be 
dissected.  The  dissectors  must  commence  at  the  hilus  of  the  lung  and 
follow  the  bronchus  and  the  vessels  into  the  interior  of  the  lung,  cutting 
away  the  lung  substance,  but  avoiding  injury  to  the  main  branches  of  the 
bronchus  and  of  the  artery,  and  the  main  tributaries  of  the  veins. 

Relations  of  the  Intra-pulmonary  Parts  of  the  Bronchi,  the  Pul- 
monary Arteries  and  the  Pulmonary  Veins.  —After  passing  through  the 
hilus  each  bronchus  descends,  in  the  substance  of  the  lung,  to  the  lower  end 
of  the  lung,  lying  nearer  the  medial  than  the  lateral  surface,  and  nearer  the 
posterior  than  the  anterior  border.     As  it  descends  it  gives  off  two  sets  of 


THORACIC  CAVITY  99 

branches  :  (i)  ventral,  which  run  towards  the  anterior  border  of  the  lung, 
and  (2)  dorsal,  which  pass  posteriorly  to  the  thick  posterior  border.  As 
these  branches  are  given  off  below  the  point  where  the  pulmonary  artery 
crosses  anterior  to  the  bronchus  they  are  called  Jiyparterial  branches.  The 
hyparterial  branches  arise  alternately,  first  a  ventral  and  then  a  dorsal 
branch,  and,  in  addition,  a  number  of  small  accessor}'  branches  are  given 
off  from  the  stem  bronchus  in  some  of  the  intervals  between  the  dorsal  and 
ventral  branches.  On  the  right  side,  the  eparterial  bronchus,  which  is  given 
off  from  the  extra-pulmonary  part  of  the  right  stem  bronchus,  supplies  the 
upper  lobe  of  the  right  lung.  The  first  ventral  hyparterial  branch  supplies 
the  middle  lobe,  and  all  the  remaining  branches  are  distributed  to  the  lower 
lobe.  On  the  left  side,  the  first  ventral  branch  goes  to  the  upper  lobe  of  the 
left  lung,  and  all  the  other  branches  go  to  the  lower  lobe. 

The  intra-pidmo7iary  part  of  each  pzdvionary  a7ieiy  descends  along  the 
postero-lateral  aspect  of  the  intra-pulmonary  part  of  the  stem  bronchus, 
between  the  ventral  branches  anteriorly  and  the  dorsal  branches  posteriorly, 
and  it  gives  off  branches  which  correspond  with  the  branches  of  the  main 
bronchus. 

The  vein  from  the  upper  lobe,  on  the  right  side,  runs  along  the  antero- 
medial  aspect  of  the  eparterial  bronchus  to  the  hilus,  where  it  joins  the 
vein  of  the  middle  lobe,  which  lies  along  the  antero-medial  border  of  the 
first  ventral  hyparterial  bronchus,  to  form  the  upper  right  pulmonary  vein. 
The  vein  from  the  lower  lobe  ascends  along  the  antero-medial  border  of 
the  intra-pulmonary  part  of  the  stem  bronchus.  On  the  left  side,  the  upper 
left  pulmonary  vein  accompanies  the  first  ventral  bronchus,  and  the  lower 
accompanies  the  intra-pulmonary  part  of  the  stem  bronchus  ;  each  vein 
lies  along  the  ventro-medial  aspect  of  the  bronchus  which  it  accompanies. 

The  Thoracic  Portions  of  the  Vagi  Nerves. — The  thoracic 
parts  of  the  vagi  nerves,  which  are  still  in  position,  should 
now  be  examined.  Both  vagi  enter  the  thorax  at  the  upper 
aperture.  The  right  vagus  descends,  through  the  superior 
mediastinum,  posterior  to  the  right  innominate  vein  and  the 
superior  vena  cava,  passing  obliquely  downwards  and  pos- 
teriorly (Fig.  12)  along  the  side  of  the  trachea,  and  between 
the  trachea  medially,  and  the  right  pleura  laterally,  to  the 
arch  of  the  azygos  vein.  Next  it  passes  between  the  trachea 
medially,  and  the  arch  of  the  azygos  vein  laterally,  and  reaches 
the  posterior  aspect  of  the  root  of  the  right  lung,  where  it  breaks 
up  into  a  number  of  branches  which  unite  with  branches  of 
the  sympathetic  trunk  to  form  the  posterior  pulmonary  plexus. 
It  emerges  from  the  plexus  as  a  single  trunk  which  runs 
downwards  and  medially,  in  the  posterior  mediastinum,  to  the 
front  of  the  oesophagus.  On  the  oesophagus  it  breaks  up  into 
branches  which  unite  with  branches  of  the  left  vagus  to  form 
the  oesophageal  plexus  (Fig.  47).  At  the  lower  end  of  the 
thorax  the  right  vagus  again  becomes  distinct ;  it  passes  to  the 
posterior  aspect  of  the  oesophagus  and  enters  the  abdomen 
through  the  oesophageal  orifice  of  the  diaphragm. 
II — la 


loo  THORAX 

Thoracic  Branches  of  the  Right  Vagtis. — Whilst  the  right 
vagus  is  in  the  superior  mediastinum  it  gives  off  a  thoracic 
cardiac  branch,  which  goes  to  the  right  half  of  the  deep 
cardiac  plexus,  and  some  anterior  pulmonary  branches  to 
the  front  of  the  root  of  the  right  lung,  where  they  join 
with  branches  of  the  cardiac  plexus  to  form  the  anterior  pul- 
monary plexus.  As  it  passes  posterior  to  the  root  of  the  lung 
it  gives  branches  to  the  bronchi  and  the  lung ;  and  in  the 
posterior  mediastinum  it  gives  branches  to  the  oesophagus, 
and  to  the  posterior  part  of  the  pericardium  and  pleura. 

The  Left  Vagus. — As  the  left  vagus  descends  through  the 
superior  m.ediastinum  it  lies  at  first  between  the  left  common 
carotid  artery  and  the  left  phrenic  nerve  anteriorly,  and  the 
left  subclavian  artery  posteriorly,  and  then  on  the  left  side 
of  the  arch  of  the  aorta.  In  the  latter  situation  it  is  crossed 
laterally  by  the  left  superior  intercostal  vein.  Below  the 
lower  border  of  the  aortic  arch  it  passes  posterior  to  the  root 
of  the  left  lung,  where  it  breaks  up  into  branches  which  enter 
into  the  formation  of  the  posterior  pulmonary  plexus.  At 
the  lower  border  of  the  root  of  the  left  lung  it  emerges  from 
the  plexus  as  two  trunks,  which  descend,  into  the  posterior 
mediastinum,  to  the  oesophagus,  where  they  unite  with 
branches  of  the  right  vagus  to  form  the  oesophageal  plexus. 
At  the  lower  end  of  the  thorax  the  left  vagus  again  becomes 
a  single  trunk  which  passes  through  the  oesophageal  orifice 
of  the  diaphragm  on  the  anterior  aspect  of  the  oesophagus. 

Thoracic  Branches  of  the  Left  Vagus. — In  the  superior 
mediastinum,  whilst  it  lies  against  the  left  side  of  the  aortic 
arch,  it  gives  off  the  left  recurrent  branch,  branches  to 
the  upper  and  anterior  part  of  the  pericardium,  and  branches 
to  the  left  anterior  pulmonary  plexus.  Posterior  to  the  root  of 
the  left  lung,  it  supplies  branches  to  the  left  bronchus  and 
the  left  lung ;  and  during  its  course  through  the  posterior 
mediastinum,  as  it  takes  part  in  the  oesophageal  plexus,  it 
gives  branches  to  the  oesophagus,  to  the  posterior  part  of  the 
pericardium,  and  to  the  left  pleura. 

The  Thoracic  Part  of  the  Left  Recurrent  Nerve. — 
The  left  recurrent  nerve  springs  from  the  trunk  of  the 
left  vagus  near  the  lower  border  of  the  left  side  of  the 
aortic  arch.  It  curves  round  the  lower  border  of  the  arch, 
posterior  and  to  the  left  of  the  ligamentum  arteriosum,  and 
passes    upwards,    posterior    and    to    the    right    of  the   arch. 


THORACIC  CAVITY  loi 

through  the  superior  mediastinum,  in  the  angle  between  the 
left  border  of  the  trachea  and  the  oesophagus,  and  posterior  to 
the  left  common  carotid  artery.  As  it  turns  round  the  arch 
it  gives  branches  to  the  deep  cardiac  plexus,  and,  as  it  ascends 
along  the  left  border  of  the  trachea,  it  gives  offsets  to  the 
trachea  and  to  the  oesophagus. 

The  Deep  Cardiac  Plexus. — The  deep  cardiac  plexus  lies 
between  the  arch  of  the  aorta  and  the  bifurcation  of  the 
trachea.  It  is  more  or  less  distinctly  separable  into  right  and 
left  parts,  and  the  right  part  is  connected  with  the  superficial 
cardiac  plexus.  The  right  part  of  the  plexus  receives  (i) 
three  cardiac  branches  from  the  cervical  part  of  the  right 
sympathetic  trunk;  (2)  the  two  cervical  cardiac  branches  of 
the  right  vagus  ;  (3)  the  cardiac  branch  of  the  right  recurrent 
nerve ;  (4)  the  thoracic  cardiac  branch  of  the  right  vagus. 
It  is  connected  \vith  the  superficial  cardiac  plexus  and  gives 
branches  to  (i)  the  right  anterior  pulmonary  plexus;  (2) 
the  right  atrium;  (3)  the  right  coronary  plexus.  The  left 
part  of  the  deep  cardiac  plexus  receives  (i)  the  middle  and 
low^er  cervical  cardiac  branches  of  the  left  sympathetic  trunk ; 
(2)  the  upper  cervical  cardiac  branch  of  the  left  vagus ;  (3) 
the  cardiac  branches  of  the  left  recurrent  nerve.  It  gives 
branches  to  (i)  the  left  anterior  pulmonary  plexus;  (2)  the 
left  atrium  ;  (3)  the  left  coronary  plexus. 

Dissection. — Cut  through  the  right  and  left  bronchi,  close  to  their  origins 
from  the  trachea  ;  then  divide  the  trachea  at  the  upper  aperture  of  the 
thorax  and  remove  its  thoracic  portion,  but  avoid  injury  to  the  vagi  and 
the  left  recurrent  nerves.  The  extra-pulmonary  parts  of  the  bronchi 
will  be  retained  in  position  by  the  bronchial  arteries  and  the  branches 
of  the  pulmonary  plexuses  ;  and  the  thoracic  part  of  the  oesophagus  will  be 
fully  exposed. 

The  Thoracic  Part  of  the  CEsophagus. — The  thoracic  part 
of  the  oesophagus  enters  the  thorax  at  the  upper  aperture, 
passes  downwards,  through  the  superior  and  posterior 
mediastina,  and  leaves,  at  the  level  of  the  tenth  thoracic 
vertebra,  by  passing  through  the  oesophageal  orifice  of  the 
diaphragm  into  the  epigastric  region  of  the  abdomen.  As  it 
enters  the  superior  mediastinum  it  lies  somewhat  to  the  left 
of  the  median  plane,  but  as  it  descends  it  passes  medially, 
gains  the  median  plane  at  the  level  of  the  fifth  thoracic 
vertebra,  and  continues  downwards  in  that  plane  to  the  level 
of  the  seventh  thoracic  vertebra.     There  it  passes  forwards 

II— 7  & 


I02 


THORAX 


and  to  the  left,  across  the  anterior  aspect  of  the  descending 
aorta  and  posterior  to  the  pericardium  (Figs.  12  and  21). 

Posterior  Relations. — In  the  superior  mediastinum  it  is  an- 
terior to  the  left  longus  colli  muscle  and  the  vertebral  column. 
In  the  upper  part  of  the  posterior  mediastinum  it  is  separated 
from  the  vertebral  column  by  (i)  the  posterior  part  of  the  oeso- 
phageal plexus,  (2)  the  upper  six  right  aortic  intercostal  arteries, 
(3)  the  thoracic  duct,  (4)  the  vena  azygos,  (5)  the  vena  hemi- 
azygos and  the  accessory  hemiazygos  vein;  and  in  the  lower  part 
by  (6)  the  oesophageal  plexus  and  (7)  the  descending  aorta. 

Anterior  Relations. — Anterior  to  it,  in  the  superior  ??iedia- 
stinum,  lie  the  trachea,  the  left  recurrent  nerve,  the  upper 
part  of  the  left  common  carotid  artery,  the  left  subclavian 
artery,  the  arch  of  the  aorta,  and  the  structures  which  lie 
anterior  to  those  already  mentioned.  As  it  passes  from  the 
superior  to  the  posterior  mediastinum  its  anterior  relations  are 
first  the  commencement  of  the  left  bronchus  and  then  the 
right  pulmonary  artery.^  In  the  posterior  mediastinmn,  the 
oesophageal  plexus  is  on  its  anterior  surface,  intervening 
between  it  and  the  posterior  wall  of  the  pericardium,  which 
separates  both  the  plexus  and  the  oesophagus  from  the 
posterior  wall  of  the  left  atrium ;  and  at  a  lower  level  the 
oesophagus  lies  posterior  to  the  diaphragm  (Fig.  21). 

Right  lateral  Relations. — In  the  superior  mediastimwi,  it  is 
in  relation  with  the  right  pleura  and  lung  and  with  the  arch 
of  the  vena  azygos  (Figs.  12  and  22),  and  in  the  posterior 
mediastinum  with  the  oesophageal  plexus  and  right  pleura 
and  lung,  until  it  passes  anteriorly  and  to  the  left,  anterior  to 
the  descending  aorta. 

left  latei-al  Relations. — In  the  siperior  mediastinum,  it  is 
in  relation  on  the  left  side  with  the  thoracic  duct,  the  left 
subclavian  artery,  the  left  pleura  and  lung,  and  the  termination 
of  the  arch  of  the  aorta.  Frofn  the  fifth  to  the  seventh  thoracic 
vertebra  its  left  lateral  relations  are  the  oesophageal  plexus  and 
the  descending  aorta  ;  and  at  its  lower  end,  as  it  Hes  anterior  to 
the  descending  aorta,  it  comes  again  into  relation  with  the 
left  pleura  and  lung. 

The  dissector  should  note  (i)  that,  after  death,  the 
oesophagus  is  somewhat  compressed  antero- posteriorly  by 
the  structures  between  which  it  fies.  It  probably  has  a 
similar  form  during  Hfe  when  empty  and  flaccid,  but  becomes 

1  Verify  this  statement  by  replacing  the  heart  in  situ. 


THORACIC  CAVITY 


103 


more  circular  when  solids  or  fluids  are  passing  along  it ;  and 
(2)  that  it  is  somewhat  constricted  at  the  level  of  the  left 
bronchus. 

An  inch  or  more  of  the  upper  part  of  the  posterior 
mediastinal  portion  of  the  tube  should  be  removed  and  dis- 
sected under  water  in  a  cork-Hned  tray.  It  will  be  found  to 
possess  from  without  inwards  the  following  coats:  (i)  an 
external  fibrous  sheath;  (2)  a  muscular  coat;  (3)  a  sub- 
mucous coat ;  and  (4)  a  mucous  internal  hning.  The 
submucous  coat  forms  a  loose  connection  between  the 
muscular  and  mucous  coats  ;  consequently,  when  the  muscular 


—  Vena  cava  inferior 


Pericardium 


CEsophagus 

Thoracic  duct 
.Vena  azygos 

Pleura 


Thoracic  aorta 


Pleura 


Fig.  50.  — Tracing  of  section  through  the  Posterior  Mediastinum 
at  the  level  of  the  eighth  thoracic  vertebra, 

coat  is  contracted  the  mucous  Hning  is  thrown  into  longi- 
tudinal folds.  The  muscular  coat  consists  of  an  external  layer 
of  longitudinal  fibres  and  an  internal  layer  of  circular  fibres. 

Aorta  Descendens. — The  descending  aorta  commences 
at  the  termination  of  the  aortic  arch,  at  the  lower  border  of 
the  left  side  of  the  fourth  thoracic  vertebra.  It  passes  down- 
wards, through  the  posterior  mediastinum,  and  it  leaves  the 
thorax  by  passing  through  the  aortic  aperture  of  the  diaphragm, 
opposite  the  lower  border  of  the  twelfth  thoracic  vertebra. 
Its  length  is  about  seven  inches.  In  the  upper  part  of  its 
extent  it  lies  to  the  left  of  the  vertebral  column ;  but  in  the 
lower  part  it  lies  anterior  to  the  column,  in  the  median  plane. 

Branches. — Branches  spring  from  both  the  anterior  and  the 
posterior  aspects  of  the  descending  aorta.  Those  from  the 
anterior    aspect    are    the    two    left    bronchial    arteries,    four 

II— 7  c 


I04 


THORAX 


oesophageal  branches,  and  some  small  and  irregular  media- 
stinal and  pericardial  branches.  The  posterior  branches  are 
nine  pairs  of  aortic  intercostal  arteries  and  one  pair  of  sub- 
costal arteries. 

Relations. — Anterior  to  the  thoracic  part  of  the  descending 
aorta,  from  above  downwards,  are  the  root  of  the  left  lung; 
the  upper  part  of  the  posterior  wall  of  the  pericardium, 
separating  the  aorta  from  the  left  atrium  ;  the  oesophagus, 
separating  the  aorta  from  the  lower  part  of  the  posterior  wall 
of  the  pericardium ;  and  the  crura  of  the  diaphragm,  which 
separate   the  lower  portion  of  the  thoracic  aorta  from  the 


Pericardium 


Diaph 


-Diaphragm 
CEsophagus 


Thoracic  aorta 
Left  pleura 


,.-  Thoracic  duct 

Right  pleura 
Vena  azygos 


Fig,  51. — Tracing  of  a  section  through  the  lower  part  of  the  Posterior 
Mediastinum,  where  its  anterior  wall  is  formed  by  the  diaphragm. 


omental  bursa  of  the  peritoneum  and  from  the  posterior 
surface  of  the  caudate  lobe  (O.T.  Spigelian)  of  the  liver. 
Posteriorly  are  the  vertebral  column,  its  own  intercostal  and 
subcostal  branches,  the  hemiazygos  and  accessory  hemiazygos 
veins ;  and  it  is  overlapped  posteriorly  in  the  upper  part  of  its 
extent  by  the  left  pleura  and  lung.  Along  its  right  side,  in  its 
whole  length,  are  the  thoracic  duct  and  the  vena  azygos,  and 
anterior  to  them,  from  the  fifth  to  the  lower  part  of  the 
seventh  thoracic  vertebra,  lies  the  oesophagus.  At  a  lower 
level  a  mass  of  areolar  tissue  separates  the  aorta  from  the 
right  pleura  and  lung.  On  its  left  side  it  is  in  relation  with 
the  left  pleura  and  lung. 

Dissection. — Turn  the  remains  of  the  lower  part  of  the  oesophagus  down- 
wards towards  the  diaphragm.  Clean  the  thoracic  duct,  the  right  aortic 
intercostal  arteries,  and  the  hemiazygos  and  accessory  hemiazygos  veins, 
which  lie  posterior  to  the  oesophagus.     Then  trace  the  thoracic  duct  in  the 


THORACIC  CAVITY 


105 


Thoracic  Duct  and  its  Tributaries, 


Lumbar  veins. 
Left  renal  vein. 
Right  renal  artery. 
Inferior  vena  cava. 
Suprarenal  gland. 
Cisterna  chyli. 
Thoracic  duct. 
Descending  thoracic 

lymph  trunk. 
Vena  azj'gos. 
^Mediastinal  lymph 

vessel. 
Superior  intercostal  vein. 
Subclavian  vein. 
Subclavian  artery. 
Clavicle. 
Scalenus  anterior 

muscle. 
Phrenic  nerve. 
Thyreo-cervlcal  trunk. 
Internal  jugular  vein. 
Vertebral  artery. 
Common  carotid  artery 
Trachea. 
Thyreoid  gland. 
Qilsophagus. 
Common  carotid  artery. 

25.  Internal  jugular  vein. 

26.  Vertebral  artery. 

27.  Thyreo-cervical  trunk. 
Common  lymph 

trunk  from  head  and 

upper  limb. 
Scalenus  anterior 

muscle. 
Subclavian  arte^>^ 
Superior  intercostal  vein 
Bronchial  lymph 

vessel. 
Vena  hemiazygos 

accessoria. 
Aorta. 
Vena  hemiazj'gos. 

36.  CEsophagus. 

37.  Descending  thoracic 
Ij-mph  trunk. 

Inferior  phrenic  artery. 
Suprarenal  gland. 
Ccfiliac  artery. 
Superior  mesenteric 

artery. 
Common  intestinal 

lymph  trunk. 
Renal  arterj-. 
Renal  vein. 
Common  lumbar 

lymph  trunk. 


To6  THORAX 

whole  of  the  thoracic  portion  of  its  course,  and  arrange  with  the  dissector 
of  the  head  and  neck  to  display  the  cervical  portion  of  its  course. 

The  Thoracic  Duct. — The  thoracic  duct  is  a  vessel  of 
small  calibre  but  of  great  importance,  for  it  conveys,  to  the 
left  innominate  vein,  the  whole  of  the  lymph  from  the  lower 
extremities,  the  abdomen  (except  that  from  part  of  the  upper 
surface  of  the  liver),  the  left  side  of  the  thorax,  including  the 
left  lung  and  pleura  and  the  left  side  of  the  heart,  the  left 
upper  extremity,  and  the  left  side  of  the  head  and  neck.  It 
is  the  upward  prolongation  of  a  dilated  sac,  the  cisterna 
chyli,  which  lies  between  the  right  crus  of  the  diaphragm  and 
the  bodies  of  the  first  and  second  lumbar  vertebrae.  It 
enters  the  thorax  through  the  aortic  orifice  of  the  diaphragm, 
lying  between  the  aorta  on  the  left  and  the  vena  azygos  on 
the  right.  It  continues  upwards  through  the  posterior 
mediastinum,  lying  between  the  descending  aorta  and  the 
vena  azygos,  anterior  to  the  right  aortic  intercostal  arteries 
and  the  hemiazygos  and  accessory  hemiazygos  veins,  and 
posterior  to  the  right  pleura  below  and  the  oesophagus  above. 
At  the  level  of  the  fifth  thoracic  vertebra  it  crosses  to  the  left 
of  the  vertebral  column,  and  then  ascends,  through  the  superior 
mediastinum,  along  the  left  border  of  the  oesophagus,  in 
contact,  on  the  left,  with  the  left  pleural  sac,  and  separated 
posteriorly  from  the  left  longus  colli  muscle  by  the  mass  of 
areolar  tissue.  Anterior  to  the  thoracic  duct,  in  the  superior 
mediastinum,  are  the  termination  of  the  aortic  arch,  the  left 
subclavian,  and  the  left  common  carotid  arteries,  in  that  order 
from  below  upwards.  At  the  upper  end  of  the  thorax  the 
thoracic  duct  enters  the  root  of  the  neck,  and,  at  the  level  of 
the  seventh  cervical  vertebra,  it  turns  laterally,  posterior  to 
the  left  common  carotid  artery,  the  left  vagus  nerve,  and  the 
left  internal  jugular  vein,  and  anterior  to  the  vertebral  artery 
and  veins,  the  thyreo-cervical  trunk  or  inferior  thyreoid  artery, 
and  the  phrenic  nerve.  Then,  turning  downwards,  anteriorly 
and  medially,  on  the  anterior  aspect  of  the  scalenus  anterior, 
it  crosses  anterior  to  the  transversa  colli  and  transversa  scapulae 
arteries,  and  terminates  in  the  upper  end  of  the  innominate 
vein,  in  the  angle  of  junction  of  its  internal  jugular  and  sub- 
clavian tributaries.  Immediately  before  its  termination  it 
receives  the  left  common  jugular  and  subclavian  lymphatic 
trunks,  unless  they  end  separately  in  one  or  other  of  the 
three  large  veins.     When  the  thoracic  duct  is  distended  it 


THORACIC  CAVITY 


107 


has  a  beaded  or  nodulated  appearance  on  account  of  the 
numerous  valves  which  lie  in  its  interior.  The  terminal 
valve  is  usually  situated  a  short  distance  from  the  point  of 
entrance  of  the  duct  into  the  left  innominate  vein. 


Clavicular  head  of  -. 
sterno-mastoid  "* 


Stemo-thj'reold  — 


Th>Teoid  gland  - — _, 

.  Phrenic  nerve '- 

Vagus"" '' 

Sternal  head  of_ 
sterno-mastoid 


Stemo-hyoid 


.  External  jugular  vein 
/     .  Platysma  reflected  with  skin 


/--»       Nervus  cutaneus  colli 


Internal  jugular  vein 


Supra-clavicular 
nerves 


Omo-hyoid 

Transverse  cervical 
vein 

Brachial  plexus 

Scalenus  anterior 
Trans.  cer%'ical  artery 
Trans,  scapular  artery 
External  jugular  vein 
Subclavius 
Cephalic  vein 
Axillarj^  vein 


Anterior  jugular  vein 
Cla^icular  facet  on  sternum 

Left  common  carotid 


Left  innominate  vein        ! 


\         First  rib 
\  \    Dome  of  left  pleura 

\         Thoracic  duct 
Internal  mammary  artery 
Phrenic  nerve 


Fig. 


53- 


-Dissection  of  the  Root  of  the  Neck  showing  the  termination 
of  the  Thoracic  Duct. 


The  Right  Lymphatic  Duct. — From  the  point  where  the 
thoracic  duct  turns  from  the  front  to  the  left  of  the 
vertebral  column  a  small  lymphatic  vessel,  which  frequently 
communicates  with  the  thoracic  duct,  may  be  traced  upwards 
along   the  front   of  the   column    to  the    root    of   the   neck. 


io8  THORAX 

where  it  ends  in  the  commencement  of  the  right  innominate 
vein.  This  is  the  right  lymphatic  duct.  Immediately  before 
its  termination  it  may  be  joined  by  the  right  common 
jugular  and  right  subclavian  lymphatic  trunks,  but,  as  a 
rule,  the  two  latter  vessels  open  separately  into  the  sub- 
clavian, the  internal  jugular,  or  the  innominate  veins  (Parsons). 
The  right  lymphatic  duct  conveys  lymph  from  the  upper  part 
of  the  right  lobe  of  the  liver,  the  right  side  of  the  thorax, 
including  the  right  pleura  and  lung  and  the  right  half  of  the 
heart,  and,  if  it  is  joined  by  the  jugular  and  subclavian  trunks, 
the  lymph  from  the  right  upper  extremity  and  the  right  side 
of  the  head  and  neck  also. 

Lymphoglandulse  Thoracales. — During  the  dissection  of  the  thorax 
the  dissector  will  have  noted  certain  groups  of  lymph  glands.  These 
are  of  considerable  importance,  for  their  enlargement  in  disease  is  not 
infrequently  the  cause  of  serious  thoracic  trouble  ;  but  whilst  some,  such 
as  the  bronchial  glands,  are  quite  obvious,  others  are  frequently  so 
small  that  they  escape  notice.  The  following  are  the  chief  groups: — (i) 
Two  chains  of  minute  glands  which  are  placed  in  relation  to  the  anterior 
thoracic  wall  and  follow  the  course  of  the  internal  mammary  vessels.  They 
are  termed  sternal  lymph  glands,  and  are  joined  by  lymphatic  vessels  from 
the  anterior  thoracic  wall,  the  mammary  glands,  the  anterior  part  of  the 
diaphragm,  and  the  upper  part  of  the  anterior  wall  of  the  abdomen.  (2)  Two 
chains  of  glands  on  the  posterior  thoracic  wall — one  on  either  side  of  the 
vertebral  column  in  relation  to  the  vertebral  extremities  of  the  ribs.  These  are 
very  minute ;  afferents  to  them  accompany  the  intercostal  vessels ;  therefore 
they  are  called  the  intercostal  lymph  glands,  and  they  receive  the  lymphatics 
of  the  posterior  thoracic  wall.  (3)  Anterior  mediastinal  lymph  glands, 
two  or  three  in  number,  which  receive  lymphatics  from  the  diaphragm 
and  upper  surface  of  the  liver.  They  occupy  the  lower  open  part  of 
the  anterior  mediastinum.  (4)  Posterior  mediastinal  lymph  glands,  which 
follow  the  course  of  the  thoracic  aorta,  and  are  joined  by  lymphatics 
from  the  diaphragm,  pericardium,  and  oesophagus.  (5)  Superior  inedia- 
stinal  lymph  glands,  an  important  group,  eight  to  ten  in  ntimber,  and 
placed  in  relation  to  the  aortic  arch  and  the  bifurcation  of  the  trachea. 
The  lymphatics  of  the  heart,  pericardium,  and  thymus  enter  these.  (6) 
Bronchial  lymph  glands,  continuous  above  with  the  preceding,  and 
massed  chiefly  in  the  interval  between  the  two  bronchi.  They  are  also 
prolonged  into  the  roots  of  the  lungs.  The  lymphatic  vessels  of  the  lungs 
pour  their  contents  into  them.  In  the  adult,  they  are  generally  dark  in 
colour,  and  sometimes  quite  black. 

Dissection. — Cut  through  the  descending  aorta  immediately  above  the 
diaphragm.  Detach  its  upper  end  from  the  left  vagus  and  the  left  recurrent 
nerve  which  were  previously  fastened  to  it,  then  draw  it  forwards  and 
divide  the  intercostal  and  subcostal  arteries,  which  arise  from  its  posterior 
surface,  close  to  their  origins  and  remove  it. 

Arterise  Intercostales. — There  are  eleven  pairs  of  inter- 
costal arteries.     The  upper  two  pairs  are  derived  indirectly 


THORACIC  CAVITY  109 

from  the  subclavian  arteries ;  the  remaining  nine  pairs  are 
branches  of  the  thoracic  part  of  the  descending  aorta. 

The  Aortic  Intercostal  Arteries. — The  nine  pairs  of  aortic 
intercostal  arteries  spring  from  the  posterior  surface  of  the 
descending  aorta,  either  separately  or  by  a  series  of  common 
trunks,  one  for  each  pair.  The  right  arteries  are  longer  than 
the  left  because  the  aorta  lies  to  the  left  of  the  median  plane  ; 
and,  since  the  descending  aorta  commences  only  at  the  level 
of  the  lower  border  of  the  fourth  thoracic  vertebra,  the  four 
or  five  highest  pairs  have  to  ascend  to  gain  the  level  of 
the  spaces  to  which  they  are  distributed. 

The  right  aortic  intercostal  arteries  run  across  the  anterior 
aspects  of  the  bodies  of  the  vertebrae,  lying  posterior  to  the 
thoracic  duct  and  the  vena  azygos;  then  they  turn  posteriorly, 
between  the  sides  of  the  bodies  of  the  vertebrcC  and  the  parietal 
pleujra ;  and,  finally,  immediately  before  they  enter  the  inter- 
costal spaces,  they  pass  between  the  sides  of  the  bodies  of  the 
vertebrae  medially  and  the  sympathetic  trunk  laterally.  The 
shorter  left  aortic  intercostal  arteries  run  posteriorly,  first 
between  the  left  pleura  and  the  bodies  of  the  vertebrae,  and 
then  between  the  sympathetic  trunk  and  the  vertebral  bodies. 
As  each  artery  enters  the  space  to  which  it  belongs  it  gives  off 
a  dorsal  branchy  which  passes  posteriorly,  between  the  vertebral 
column  medially  and  the  anterior  costo-transverse  ligament 
laterally  \  it  gives  off  a  spinal  twig,  which  enters  the  verte- 
bral canal  through  the  corresponding  intervertebral  foramen  ; 
then  it  divides  into  a  medial  and  a  lateral  branch  which 
accompany  the  medial  and  lateral  divisions  of  the  posterior 
branch  of  the  corresponding  thoracic  nerve.  After  giving  off 
the  dorsal  branch,  the  trunk  of  the  artery  runs  laterally,  along 
the  upper  border  of  the  space  to  which  it  belongs,  at  first 
anterior  to  the  posterior  intercostal  membrane,  and  then 
between  the  internal  and  external  intercostal  muscles.  Its 
further  course  has  been  described  already  (p.  6).  As  it  passes 
along  the  upper  border  of  the  intercostal  space,  in  the  shelter 
of  the  subcostal  groove  of  the  rib,  it  is  situated  between 
the  intercostal  vein  above  and  the  anterior  branch  of  the 
thoracic  nerve  below. 

The  Subcostal  Arteries. — The  subcostal  arteries  are  the 
last  pair  of  branches  which  spring  from  the  posterior  aspect 
of  the  thoracic  part  of  the  descending  aorta.  They  enter 
the   abdomen,   by  passing  beneath   the    lateral  lumbo-costal 


no  THORAX 

arches,   and   they   run,    in    company   with    the   last   thoracic 
nerves,  along  the  lower  borders  of  the  last  pair  of  ribs. 

Arteriae  Intercostales  Supremae. — The  superior  intercostal 
arteries,  which  supply  the  upper  two  intercostal  spaces  on 
each  side,  are  derived  from  the  costo-cervical  branches  of 
the  subclavian  arteries  (Fig.  5).  Each  superior  intercostal 
artery  commences  at  the  level  of  the  upper  border  of  the 
neck  of  the  first  rib.  It  descends  anterior  to  the  neck  of 
the  rib,  posterior  to  the  parietal  pleura  and  between  the  first 
thoracic  ganglion  of  the  sympathetic  trunk  medially  and 
the  first  thoracic  nerve ;  which  is  passing  upwards  to  the 
brachial  plexus,  laterally  (Fig.  5).  At  the  lower  border  of 
the  neck  of  the  first  rib  it  gives  off  the  posterior  inter- 
costal artery  to  the  first  intercostal  space ;  then  it  crosses 
anterior  to  the  neck  of  the  second  rib,  and,  turning  later- 
ally, it  becomes  the  posterior  intercostal  artery  of  the  second 
space. 

Nervi  Intercostales. — The  intercostal  nerves  are  the 
anterior  branches  of  the  thoracic  nerves.  They  pass  laterally 
in  company  with  the  arteries.  The  twigs  which  connect 
them  with  the  sympathetic  ganglia  have  been  noted  already 
(p.  26).  Each  nerve  lies  at  a  lower  level  than  the  corre- 
sponding artery,  and  is  at  first  placed  between  the  posterior 
intercostal  membrane  and  the  pleura,  and  then  between 
the  two  muscular  strata.  The  further  course  of  the  nerves 
is  described  on  p.  5. 

The  first  thoracic  nerve  runs  upwards,  anterior  to  the  neck 
of  the  first  rib,  to  join  the  brachial  plexus.  It  gives  a  small 
branch  to  the  first  intercostal  space,  but  this  nerve,  although 
it  is  disposed  after  the  manner  of  an  intercostal  nerve,  does 
not  furnish,  as  a  rule,  a  lateral  cutaneous  or  an  anterior 
branch.  The  second  intercostal  nerve,  as  a  rule,  sends  a  branch 
upwards,  anterior  to  the  neck  of  the  second  rib,  to  join  that 
portion  of  the  first  thoracic  nerve  which  enters  the  brachial 
plexus.  This  communicating  twig  is  usually  minute  and  in- 
significant, but  sometimes  it  is  a  large  nerve ;  when  this  is 
the  case,  the  intercosto -brachial  nerve  (O.T.  intercosto- 
humeral),  or  lateral  cutaneous  branch  of  the  second  intercostal 
nerve,  is  very  small  or  altogether  absent. 

Venae  Intercostales. — The  intercostal  veins  differ  in  their 
arrangement  upon  the  two  sides  of  the  body.  On  the  right 
side  they  terminate  in  three  different  ways  : — 


THORACIC  CAVITY  m 

1.  The  intercostal   vein   of  the  first   or  highest  space  joins  the   right 

innominate  vein  (sometimes  the  vertebral  vein). 

2.  The  intercostal  veins  of  the  second  and  third  spaces  (and  sometmies 

that  of  the  fourth  space)  unite  into  a  common  trunk,  termed  the 
Hght  superior  intercostal  vein,  which  joins  the  upper  part  of  the 
vena  azygos. 

3.  The  intercostal  veins  of  the  lower  eight  spaces  join  the  vena  azygos. 

On  the  left  side  of  the  body  four  modes  of  termination  may 
be  recognised :  — 

1.  The  intercostal  vein  of  the  first  space  joins  the /^//  innominate  vein 

(sometimes  the  vejiebral  vein). 

2.  The  intercostal  veins  of  the  second  and  third  spaces  (and  sometimes 

that  of  the  fourth  space)  converge  and  by  their  union  form  a  single 
trunk,  termed  the  left  stipeHor  intercostal  vein,  which  crosses  the 
arch  of  the  aorta  and  joins  the  left  innominate  vein  independently 
of  the  first  intercostal  vein.  The  union  with  the  left  innominate 
vein  may  be  absent,  and  then  the  trunk  formed  by  the  veins  of 
the  second  and  third  spaces  joins  the  accessory  hemiazygos  vein. 

3.  The  intercostal  veins  of  the  fourth,  fifth,  sixth,  seventh,  and  eighth 

spaces  terminate  in  the  accessory  hemiazygos  vein  (O.T.  vena  azygos 
minor  superior),  which  crosses  posterior  to  the  aorta  and  joins  the 
hemiazygos  vein,  or  it  ends  directly  in  the  vena  azygos. 

4.  The  intercostal  veins  of  the  ninth,  tenth,  and  eleventh  spaces  join  the 

hemiazygos  vein  (O.T.  vena  azygos  minor  infeHor). 

Vena  Azygos  (O.T.  Vena  Azygos  Major).  — This  has 
already  been  studied,  but  'should  now  be  revised  (p.  29), 
and  then  the  dissector  should  examine  the  hemiazygos  and 
accessory  hemiazygos  veins. 

Vena  Hemiazygos  Accessoria. — The  accessory  hemiazygos 
vein  is  formed,  on  the  left  side  of  the  body,  by  the  union  of  the 
intercostal  veins  of  the  fourth,  fifth,  sixth,  seventh,  and  eighth 
spaces.  It  communicates  above  with  the  left  superior  inter- 
costal vein,  which  carries  the  blood  from  the  second  and  third 
intercostal  spaces  to  the  left  innominate  vein ;  and  it  receives 
the  left  bronchial  veins.  At  the  level  of  the  seventh  thoracic 
vertebra  it  crosses  to  the  right,  posterior  to  the  aorta  and 
thoracic  duct,  and  ends  by  joining  either  the  hemiazygos  vein 
or  the  vena  azygos.  In  addition  to  the  intercostal  veins  it 
receives  the  left  bronchial  veins. 

Vena  Hemiazygos  (O.T.  Vena  Azygos  Minor  Inferior). — 
This  vein  takes  origin  within  the  abdomen  as  the  left 
ascendi?ig  lumbar  vein.  It  enters  the  thorax  by  piercing 
the  left  crus  of  the  diaphragm,  and  is  continued  upwards, 
upon  the  vertebral  column,  as  far  as  the  eighth  or  seventh 
thoracic  vertebra.      At  this  point  it  turns  to  the  right,  and. 


112  THORAX 

crossing  posterior  to  the  aorta  and  the  thoracic  duct,  it  joins 
the  vena  azygos.  Before  it  terminates  it  may  receive  the 
accessory  hemiazygos  vein. 

The  thoracic  tributaries  of  this  vein  are  the  intercostal 
veins  of  the  lower  three  spaces  of  the  left  side  and  the  left 
subcostal  vein.  In  the  abdomen  it  receives  the  upper  two 
left  lumbar  veins. 

The  Anterior  Intercostal  Veins. — The  blood  is  drained 
from  the  anterior  part  of  the  thoracic  .wall  by  veins  which 
accompany  the  intercostal  branches  of  the  internal  mammary 
arteries.     They  terminate  in  the  internal  mammary  veins. 

The  veins  of  the  thoracic  parietes  are  extremely  variable,  and  the 
description  given  above  must  be  looked  upon  as  representing  merely  their 
more  usual  arrangement. 


THORACIC  JOINTS. 

The  dissector  should  now  complete  the  dissection  of  the 
thorax  by  an  examination  of  the  various  thoracic  joints. 

Dissection.  — When  the  portion  of  the  sternum  with  the  cartilages  of  the 
ribs,  which  was  laid  aside,  is  studied,  the  following  joints  will  be  noted  : 
inter-sternal,  costo-sternal,  and  inter-chondral.  Very  little  dissection  is 
necessary.  After  the  ligaments  have  been  defined,  the  dissector  should 
remove  a  thin  slice  from  the  anterior  aspect  of  each  articulation,  in  order 
that  the  interior  of  the  joint  may  be  displayed. 

Synchondrosis  Sternalis. — The  joint  between  the  manu- 
brium and  the  body  of  the  sternum  is  a  synchondrosis.  The 
opposing  surfaces  of  bone  are  covered  with  a  layer  of  hyaline 
cartilage,  and  are  united  by  intermediate  fibro-cartilage.  The 
joint  is  supported  by  some  anterior  and  posterior  longitudinal 
fibres  which  are  developed  in  connection  with  the  strong  and 
thick  periosteum.  The  posterior  ligament  is  the  stronger  of 
the  two.  The  joint  between  the  body  of  the  sternum  and  the 
xiphoid  process  is  also  a  synchondrosis  till  middle  life,  at 
which  period  the  two  parts  become  ossified  together. 

Sterno-chondral  Articulations. — Seven  ribs  articulate  with 
each  side  of  the  sternum  by  means  of  their  cartilages. 

The  articulations  of  the  first  and  the  sixth  are  peculiar,  inasmuch  as 
they  articulate  with  single  pieces  of  the  sternum,  viz.  with  the  manubrium 
and  the  lowest  piece  of  the  body,  respectively  ;  whereas  each  of  the  cartilages 
of  the  other  true  ribs  articulates  with  two  segments  of  the  sternum.  The 
cartilage  of  the  first  rib  is  implanted  upon  the  side  of  the  manubrium 


THORACIC  JOINTS  113 

without  any  synovial  membrane,  or  other  material,  intervening.  The 
second  costal  cartilage  is  usually  separated  from  the  sternum  by  two 
synovial  cavities,  between  which  an  interarticular  ligament  is  developed. 
In  the  case  of  the  other  joints  it  is  more  common  to  find  a  single  synovial 
cavity  and  no  interarticular  ligament.  There  is,  however,  considerable 
variety  in  these  articulations,  and  a  synovial  membrane  is  very  frequently 
wanting  altogether  in  the  sterno-chondral  joint  of  the  seventh  costal 
cartilage. 

With  the  exception  of  the  first,  which  is  a  synchondrosis, 
the  sterno-chondral  joints  belong  to  the  diarthrodial  variety. 
They  are  provided  with  anterior  and  posterior  ligaments,  and 
also,  in  those  cases  where  the  joint  presents  a  double  synovial 
cavity,  with  an  interarticular  ligament. 

A?itenor  and  posterior  ster?io-costal  radiate  ligaments.  These 
are  strong,  flattened  bands  of  fibres  which  radiate  from  the 
extremities  of  the  rib-cartilages  and  blend  with  the  periosteum 
on  the  anterior  and  posterior  surfaces  of  the  sternum.  The 
intera7iicular  liga?nejits  are  feeble  bands  which  pass  from  the 
tips  of'the  rib-cartilages  to  the  sternum,  and  divide  the  articu- 
lations in  which  they  exist  into  an  upper  and  a  lower  com- 
partment, each  of  which  is  lined  with  a  synovial  stratum. 

Inter-cliondral  Articulations.  —  Interchondral  joints  are 
formed  between  the  adjacent  margins  of  the  ribs  from  the 
sixth  to  the  tenth.  The  joint  cavities  are  surrounded  by 
ordinary  capsular  ligaments,  each  of  which  is  lined  internally 
with  a  synovial  stratum ;  they  are,  therefore,  diarthrodial 
joints. 

Costo-vertebral  Articulations. — The  costo-vertebral  joints 
are  separable  into  two  groups,  capitular  and  costo-transverse. 

The  capitular  articulations  are  the  joints  between  the  heads 
of  the  ribs  and  the  bodies  of  the  vertebras  and  the  interverte- 
bral fibro-cartilages ;  they  are  diarthrodial  joints.  With  the 
exceptions  of  the  first  and  the  last  three  ribs,  the  head  of 
every  rib  articulates  with  the  bodies  of  two  adjacent  vertebrae 
and  the  intervening  intervertebral .  fibro-cartilage,  and  it  is 
connected  with  them  by  an  articular  capsule  and  an  inter- 
articular ligament.  The  interarticular  ligament  connects  the 
intervertebral  fibro-cartilage  with  the  ridge  which  separates 
the  two  facets  on  the  head  of  the  rib.  It  is  united,  anteriorly 
and  posteriorly,  with  the  capsule,  and  separates  the  joint  cavity 
into  an  upper  and  a  lower  compartment.  The  anterior  part 
of  the  capsule  is  specialised  into  three  radiating  bands  which 
form   the  7-adiate  ligament.     The  upper  and  lower  bands  go 

VOL.   II S 


114 


THORAX 


to  the  corresponding  vertebrae,  whilst  the  intermediate  band 
is  attached  to  the  intervertebral  fibro-cartilage.  The  capitular 
joints  of  the  first,  and  the  tenth,  eleventh,  and  twelfth  ribs  are 
each  formed  between  the  head  of  the  rib  and  the  correspond- 
ing vertebra.  The  interarticular  ligament  is  absent;  therefore 
each  joint  possesses  only  one  cavity.  The  anterior  parts  of 
the  capsules  of  these  joints  are  not,  as  a  rule,  specialised  into 
radiate  bands. 

The  Costo-transverse  Articulations  are  the  joints  formed 

Anterior  longitudinal  ligament 
Rib 


Three  slips  I 
of  radiate-!  ^ 
ligament  I  ^ 


Anterior 

costo-transverse 

ligament 


Fig.  54. — Anterior  aspect  of  the  Costo-vertebral  Joints  ;  also  Anterior 
Longitudinal  Ligament  of  Vertebral  Column. 

between  the  necks  and  the  tubercles  of  the  ribs  and  the  trans- 
verse processes  of  the  vertebrae. 

The  tubercle  of  each  rib,  with  the  exception  of  the 
eleventh  and  twelfth,  articulates  with  the  tip  of  the  transverse 
process  of  the  vertebra  of  the  same  number,  by  a  circular 
articular  facet  which  is  surrounded  by  an  articular  capsule 
lined  with  a  stratum  synoviale.  The  joint  is,  therefore,  a  diar- 
throdial  joint  and  the  upper  and  posterior  part  of  the  capsule 
is  greatly  thickened,  and  is  called  the  ligament  of  the  tubercle 
(O.T.  posterior  costo-transverse  Ugameni).  In  addition  to  the 
capsule  and  its  posterior  thickening  there  are  three  accessory 


THORACIC  JOINTS  115 

costo-transverse  bands,  the  anterior  and  posterior  costo-trans- 
verse  ligaments  and  the  Ugament  of  the  neck  of  the  rib. 
The  anterior  costo  -  transverse  ligament  ascends  from  the 
anterior  margin  of  the  upper  border  of  the  neck  of  the  rib 
to  the  lower  border  of  the  transverse  process  above.  The 
posterior  costo-transverse  ligament  passes  upwards  from  the 
posterior  part  of  the  upper  border  of  the  neck  of  the  rib  to 
the  junction  of  the  lamina  and  the  transverse  process  of 
the  vertebra  above ;  and  the  ligament  of  the  neck  of  the  rib 
(O.T.  middle  costo-transverse  ligament^  connects  the  posterior 
aspect  of  the  neck  of  the  rib  with  the  anterior  aspect  of  the 
transverse  process  of  the  vertebra  of  the  same  number. 

In  the  case  of  the  eleventh  rib  the  costo-transverse  hga- 
ments  are  rudimentary  or  absent,  and  in  the  case  of  the 
twelfth  rib  they  are  usually  entirely  absent. 

Intervertebral  Articulations. — The  bodies  of  the  vertebrae 
are  held  together  by  a  series  of  synchondrodial  joints,  sup- 
ported anteriorly  by  an  anterior  longitudinal  ligament,  and 
posteriorly  by  a  posterior  longitudinal  ligament.  The  vertebral 
arches^  by  means  of  the  articular  processes,  form  a  series  of 
diarthrodial  joints  surrounded  by  capsular  ligaments,  each 
capsule  being  lined  with  a  synovial  stratum.  Certain  ligaments 
pass  between  different  portions  of  the  vertebral  arches  and  their 
processes,  viz.,  the  ligamenta  flava  between  adjacent  laminae, 
the  inter-transverse,  the  inter-spinous,  and  the  supra-spinous 
ligaments. 

The  laminae  and  the  spinous  processes  of  the  vertebrae  have  been 
removed  by  the  dissector  of  the  head  and  neck  in  opening  up  the  vertebral 
canal  to  display  the  spinal  medulla.  Consequently,  the  ligamenta  flava, 
the  inter-spinous  and  supra-spinous  ligaments,  cannot  be  seen  at  present. 

The  anterior  longitudinal  liga?}ie?it  (O.T.  a?iterior  common 
Ugament)  is  situated  anterior  to  the  bodies  of  the  vertebrae, 
and  extends  from  the  atlas  vertebra  above  to  the  first  piece 
of  the  sacrum  below.  It  consists  of  stout  glistening  fibrous 
bands,  which  are  firmly  attached  to  the  margins  of  the  verte- 
bral bodies  and  to  the  intervertebral  fibro-cartilages.  The 
most  superficial  fibres  are  the  longest,  and  extend  from  a 
given  vertebra  to  the  fourth  or  fifth  below  it.  The  deeper 
fibres  have  a  shorter  course,  and  pass  between  the  borders 
of  two,  three,  or  four  adjacent  vertebrae.  The  dissector 
cannot  fail  to  notice  that  the  origin  of  the  longus  colli  muscle 
is  inseparably  connected  w^ith  this  ligament. 
II — 8  a 


ii6 


THORAX 


Root  of 
arch  (cut) 
(O.T.  pedicle) 


Posterior 

longitudinal 

ligament 


The  posterior  longitudinal  ligament  (O.T.  posterior  co7nmon 
ligament)  is  placed  on  the  posterior  aspects  of  the  vertebral 
bodies,  and  therefore  within  the  vertebral  canal.  It  is  firmly 
connected  to  the  margins  of  the  vertebral  bodies  and  to  the 
intervertebral  fibro-cartilages,  but  is  separated  from  the  central 
parts  of  the  bodies  by  some  loose  connective  tissue  and  by  a 
plexus  of  veins.  It  is  constricted  where  it  covers  this  venous 
plexus,  but  widens  out  opposite  the  fibro-cartilages.  It  there- 
fore presents  a  scalloped  or 
denticulated  appearance. 

The  intervertebral  fibro- 
cartilages  are  a  series  of 
discs  of  white  fibro-car- 
tilage,  thicker  anteriorly 
than  posteriorly,  which  are 
interposed  between  the 
bodies  of  adjacent  vertebrae. 
The  peripheral  part  of  each 
disc,  annulus  fibrosus,  is 
tough  and  fibrous ;  the 
central  portion,  nucleus 
pulposus,  is  soft  and  pulpy. 
The  discs  increase  the 
elasticity  of  the  spine, 
and  tend  to  restore  it  to 
its  natural  curvature  after 
it  has  been  deflected  by 
muscular  action. 

The     intervertebral 
fibro  -  cartilages    constitute 
the   main   bond    of  union 
between  the  bodies  of  the  vertebrae,  but,  except  in  old  people, 
they  are  not  directly  attached  to  the  bone.     A  thin  layer  of  en- 
crusting hyaline  cartilage  coats  the  opposing  vertebral  surfaces. 

Vertical  and  horizontal  sections  must  be  made  through  two  or  more  of 
the  fibro-cartilages,  in  order  that  their  structure  may  be  displayed. 

The  intertransverse  ligaments  are  feeble  bands  which  pass 
between  the  tips  of  the  transverse  processes.  In  the  lower 
part  of  the  thoracic  region  they  are  intimately  blended  with 
the  intertransverse  muscles :  in  the  middle  and  upper  parts 
of  the  thoracic  region  they  entirely  replace  the  muscles. 


Inter- 
vertebral 
fibro- 
cartilage 


Fig.  55. — Posterior  Longitudinal  Liga- 
ment of  the  Vertebral  Column.  The 
vertebral  arches  have  been  removed 
from  the  vertebras. 


FACE  AND  FRONTAL  REGION  OF  HEAD     117 


HEAD   AND    NECK. 

The  dissectors  of  the  Head  and  Neck  begin  work  as  soon 
as  the  subject  is  brought  into  the  room.  During  the  first 
three  days,  whilst  the  body  is  in  the  lithotomy  posture,  they 
dissect  the  face,  the  anterior  part  of  the  eyelids,  the  superficial 
part  of  the  nose,  and  the  anterior  part  of  the  scalp.  During 
the  following  five  days,  when  the  body  is  lying  on  its  back, 
they  dissect  the  posterior  triangle,  and  complete  the  dissection 
of  the  scalp. 

It  is  only  by  dissecting  the  face  at  this  period,  whilst 
the  parts  are  in  good  condition,  that  the  dissector  can 
gain  any  satisfactory  idea  of  its  component  parts ;  and  it  is 
essential  that  the  contents  of  the  posterior  triangle,  which 
is  such  an  important  surgical  region,  should  be  displayed 
before  the  dissector  of  the  arm  has  disturbed  its  posterior 
boundary. 

The  first  day  should  be  devoted  to  the  examination  of  the  anterior  part 
of  the  frontal  region  of  the  head  and  the  face,  the  study  of  the  surface 
anatomy  of  the  ocular  appendages,  the  reflection  of  the  skin,  and  the  clean- 
ing of  the  superficial  muscles  of  the  face  and  anterior  part  of  the  scalp. 
On  the  second  day  the  dissectors  should  display  the  superficial  surface  of 
the  parotid  gland  ;  they  should  also  find  and  clean  the  superficial  vessels 
and  nerves,  and  trace  them  to  their  terminations.  On  the  third  day  the 
superficial  muscles  must  be  reflected,  and  the  deeper  vessels  and  nerves 
must  be  exposed  and  cleaned,  and  the  auricle  should  be  examined  and 
dissected.  On  the  fourth  day,  when  the  body  has  been  placed  upon  its 
back,  the  dissectors  should  commence  the  dissection  of  the  posterior 
triangle  of  the  neck,  and  should  complete  that  part  of  the  dissection  in 
three  days.  On  the  seventh  day  they  should  complete  the  examination 
of  the  scalp.  The  eighth  day  should  be  devoted  to  a  final  study  of  the 
brachial  plexus  in  association  with  the  dissectors  of  the  upper  extremity. 


FACE    AND    FRONTAL    REGION    OF    HEAD. 

The  dissectors  should  commence  the  study  of  the  face  and 
frontal  region  by  an  examination  of  the  bony  prominences 
and  ridges  in  the  area  to  be  dissected. 

In  the  centre  of  the  facial  area  is  the  prominent  outer 
portion  of  the  nose,  consisting  of  a  lower  mobile  part  formed 
mainly  by  skin  and  cartilage,  and  an  upper  rigid  portion 
formed    by   the    nasal    bones   and    the    frontal   processes    of 


ii8  HEAD  AND  NECK 

the  maxillge.  On  either  side  of  the  nose  are  the  sockets 
for  the  eyeballs,  each  of  which  is  bounded  above  by  the 
supra-orbital  margin  of  the  frontal  bone  and  below  by  the 
orbital  margins  of  the  maxilla  and  the  zygomatic  bone 
(O.T.  malar).  The  supra-  and  infra-orbital  margins  meet 
laterally  in  the  region  of  the  cheek  bone  (zygomatic).  From 
the  posterior  part  of  the  zygomatic  bone,  the  zygomatic 
arch,  formed  partly  by  the  zygomatic  and  partly  by  the 
temporal  bone,  extends  posteriorly  to  the  ear.  Above  the 
zygomatic  arch  is  the  region  of  the  temporal  fossa,  which 
is  bounded  superiorly  by  the  temporal  line.  The  line 
terminates  anteriorly  in  the  lateral  part  of  the  supra-orbital 
margin.  Above  the  medial  part  of  the  supra-orbital  margin 
the  superciliary  arch  can  be  felt,  and  at  a  higher  level, 
above  the  lateral  part  of  the  supra-orbital  margin,  lies  the 
frontal  tuber.  The  region  above  the  nose  and  between 
the  medial  ends  of  the  superciliary  arches  is  the  glabella. 

Below  the  zygomatic  arch  lies  the  ramus  of  the  mandible 
covered  by  the  masseter  muscle ;  and  extending  anteriorly 
from  the  lower  end  of  the  ramus  is  the  body  of  the  mandible. 
A  line  dropped  vertically  through  the  junction  of  the  medial 
third  with  the  lateral  tw^o-thirds  of  the  supra-orbital  margin, 
will  cut  through  the  supra-orbital  notch  of  the  frontal  bone, 
the  infra-orbital  foramen  of  the  maxilla,  and  the  mental  foramen 
of  the  mandible,  all  three  of  which  may  be  felt  if  firm  pressure 
is  made  in  the  proper  situations.  The  first,  which  lies  in  the 
supra-orbital  margin,  transmits  the  supra-orbital  vessels  and 
nerve.  The  second  is  placed  about  half  an  inch  below  the 
infra-orbital  margin.  It  transmits  the  infra-orbital  vessels  and 
nerve.  The  third  lies  midway  between  the  second  premolar 
tooth  of  the  mandible  and  the  lower  border  of  the  mandible ; 
it  transmits  the  mental  branches  of  the  inferior  alveolar  vessels 
and  nerve. 

After  the  bony  points  of  the  region  have  been  studied, 
the  surface  anatomy  of  the  ocular  appendages  should  be 
examined.  Under  this  head  are  included  (i)  the  eyebrows; 
(2)  the  eyelids;  (3)  the  conjunctiva. 

The  eyebrows  are  two  curved  tegumentary  projections 
placed  over  the  supra-orbital  arch  of  the  frontal  bone ;  they 
intervene  between  the  forehead  above  and  the  ocular  regions 
below.  The  short  stiff  hairs  which  spring  from  the  eyebrows 
have  a  lateral  inclination. 


FACE  AND   FRONTAL  REGION   OF   HEAD     119 

The  eyelids  (palpebrae)  are  the  semilunar  curtains  provided 
for  the  protection  of  each  eyeball.  The  upper  lid  is  the 
longer  and  much  the  more  movable  of  the  two.  When  the 
eye  is  open,  the  margins  of  the  two  lids  are  slightly  concave 
and  the  interval  between  them,  riJiia  palpebrarum^  is  elliptical 
in  outline.  When  the  eye  is  closed,  and  the  margins  of  the 
lids  are  in  apposition,  the  rima  palpebrarum  is  reduced  to  a 


^Margin  of  the  upper  eye- 
lid with  openings  of 
ducts  of  tarsal  glands 


Papilla  lacrimalis  with 
punctum  lacrimale  on 
the  summit 


Plica  semilunaris 

Caruncula  lacrimalis 
Papilla  lacrimalis 


—    Opening  of  tarsal  glands 


Tarsal  glands 
shining  through  the 
conjunctiva 


Fig.  56.— Eyelid  slightly  everted  to  show  the  Conjunctiva  (enlarged). 

nearly  horizontal  line.  Owing  to  the  greater  length  and 
mobility  of  the  upper  Hd,  the  rima,  in  this  condition,  is  placed 
below  the  level  of  the  cornea  or  clear  part  of  the  eyeball. 

At  the  extremities  of  the  rima  palpebrarum  the  eyelids 
meet  and  form  the  palpebral  co7nmissures,  and  immediately 
lateral  to  the  medial  commissure  the  rima  expands  into  a 
small  triangular  space  called  the  lams  lacrifnalis.  If  the 
dissector  now  examines  the  free  margins  of  the  Uds  he  will 
note    that    to  the  lateral  side    of   the  lacus   lacrimalis    they 


I20  HEAD  AND  NECK 

are  flat,  and  that  in  each  case  the  eyelashes  project  from 
the  anterior  border,  whilst  the  tarsal  glands  open  along  the 
posterior  border,  a  distinct  interval  intervening  between  the 
cilia  and  the  mouths  of  the  glands.  On  the  other  hand, 
the  small  portion  of  the  margin  of  each  eyelid  which  bounds 
the  lacus  lacrimalis  is  more  horizontal  in  direction,  somewhat 
rounded,  and  destitute  both  of  eyelashes  and  of  tarsal  glands. 
At  the  very  point  where  the  eyelashes  in  each  eyelid  cease, 
and  the  palpebral  margin  becomes  rounded,  a  minute  emi- 
nence with  a  central  perforation  will  be  seen.  The  eminence 
is  the  papilla  lacrimalis^  whilst  the  perforation,  called  the 
punctum  lacrimale,  is  the  mouth  of  the  lacrimal  duct,  which 
conveys  away .  the  tears.  Endeavour  to  pass  a  bristle  into 
each  of  the  orifices.  The  upper  duct  at  first  ascends,  whilst 
the  lower  one  descends,  and  then  both  run  horizontally  to  the 
lacrimal  sac. 

The  conjunctiva  is  the  membrane  which  lines  the  deep 
surfaces  of  the  lids,  and  is  reflected  from  them  on  to  the 
anterior  aspect  of  the  eyeball.  At  the  margins  of  the  lids  it 
is  continuous  with  the  skin,  whilst,  through  the  puncta  lacri- 
malia  and  the  lacrimal  ducts,  it  becomes  continuous  with 
the  lining  membrane  of  the  lacrimal  sac.  The  line  of  re- 
flection of  the  conjunctiva  from  the  lids  on  to  the  eyeball  is 
termed  the  fornix  conjunctiv(B.  Owing  to  the  greater  depth  of 
the  upper  lid,  the  conjunctival  recess  between  the  upper  lid 
and  the  eyeball  is  of  greater  extent  than  that  of  the  lower  lid. 
The  conjunctiva  is  loosely  connected  with  the  eyelids  on  the 
one  hand,  and  with  the  sclera  of  the  eyeball  on  the  other. 
Over  the  cornea  the  membrane  becomes  thinned  down  to  a 
mere  epithelial  covering,  which  is  closely  adherent. 

In  connection  with  the  conjunctiva,  the  plica  semilunaris 
and  the  caruncula  lacrimalis  must  be  examined.  The 
caruncula  is  the  reddish  fleshy -looking  elevation  which 
occupies  the  centre  of  the  lacus  lacrimalis.  From  its  surface 
a  few  minute  hairs  project.  The  plica  semilunaris  is  of  interest 
because  in  the  human  eye  it  is  the  rudimentary  representative 
of  the  membrana  nictitans,  or  third  eyelid,  found  in  many 
animals.  It  is  a  small  vertical  fold  of  conjunctiva,  which  is 
placed  immediately  to  the  lateral  side  of  the  caruncula,  and  it 
slightly  overlaps  the  eyeball  at  this  point. 

Dissection. — Distend  the  eyelids  slightly  by  placing  a  little  tow  or  cotton 
wool  steeped  in  preservative  solution  in  the  conjunctival  sac ;  then  stitch 


FACE  AND  FRONTAL  REGION  OF  HEAD     121 

the  margins  of  the  lids  together.  Distend  the  cheeks  and  lips  slightly  by 
placing  tow  or  cotton  wool  steeped  in  preservative  solution  in  the  vestibule 
of  the  mouth— that  is,  between  the  cheeks  and  lips  externally  and  the  teeth 
and  gums  internally  ;  then  stitch  the  red  margins  of  the  lips  together. 

Reflect  the  skin  by  means  of  three  incisions,  a  median  longitudinal  and 
two  transverse.  Commence  the  median  incision  midway  between  the  root 
of  the  nose  and  the  external  occipital  protuberance,  carry  it  anteriorly  to  the 
forehead  and  then  downwards  along  the  median  line  of  the  forehead,  the 
nose  and  the  lips,  to  the  tip  of  the  chin.  Commence  the  upper  horizontal 
incision  at  the  level  of  the  rima  palpebrarum  ;  carry  it  laterally  from  the 
longitudinal  incision  to  the  medial  commissure,  then  round  the  margins  of 
the  rima  to  the  lateral  commissure,  and,  finally,  posteriorly  to  the  ear.  The 
lower  horizontal  incision  should  run  from  the  angle  of  the  mouth  to  the 
posterior  border  of  the  ramus  of  the  mandible.  Reflect  the  upper  and 
middle  flaps  and  leave  them  attached  posteriorly.  Reflect  the  lower  flap 
downwards  to  the  lower  border  of  the  mandible.  Note,  whilst  reflecting 
the  skin,  that  many  of  the  superficial  fibres  of  the  facial  muscles  are 
implanted  into  its  deep  surface.  It  is  these  fibres  which  tend  to  displace 
the  margins  of  wounds  of  the  face,  and  necessitate  the  application  of 
numerous  and  firmly  tied  sutures  in  order  to  secure  quick  and  accurate 
union.  Whilst  reflecting  the  skin  the  dissector  must  be  careful  to  keep  his 
knife  playing  against  its  deep  surface  ;  otherwise  he  is  certain  to  injure  the 
sphincter  muscle  of  the  eyelids,  and  the  superficial  extrinsic  muscles  of  the 
ear  which  lie  in  the  temporal  region. 

After  the  skin  is  reflected  the  superficial  muscles  must  be 
cleaned.  That  which  will  first  attract  attention  is  the  orbicu- 
laris oculi  around  the  orbit.  Above  the  orbicularis  oculi  is  the 
frontalis  belly  of  the  epicranial  muscle.  To  the  medial  side 
of  the  orbicularis  oculi  Ue  the  muscles  of  the  nose,  and  below 
it  the  muscles  of  the  upper  lip  pass  downwards  to  the 
orbicularis  oris.  Passing  anteriorly  and  upwards,  over  the 
posterior  part  of  the  lower  border  of  the  mandible,  are  the 
upper  and  posterior  fibres  of  the  platysma,  and  more  medially 
are  the  muscles  of  the  lower  lip. 

Commence  with  the  Orbicularis  Oculi  (O.T.  Orbicularis 
Palpebrarum). — Pull  the  eyelids  laterally  and  note  a  prominent 
cord-like  band  which  extends  from  the  frontal  process  of  the 
maxilla  to  the  medial  commissure,  where  it  becomes  continuous 
with  both  eyeUds ;  this  is  the  medial  palpebral  ligament 
(O.T.  internal  tarsal  ligament).  A  somewhat  similar  band,  the 
lateral  palpebral  raphe  (O.T.  external  tarsal  ligament),  extends 
from  the  lateral  commissure  to  the  zygomatic  bone.  After 
the  medial  palpebral  ligament  has  been  recognised,  clean  first 
the  thicker  orbital  part  of  the  orbicularis  oculi,  which  covers 
the  superficial  bony  boundaries  of  the  orbit,  and  then  the 
thinner  palpebral  portion,  which  lies  in  the  eyelids.  The 
palpebral  part  is  not  only  thin  but  also  pale,  and  its  fibres,  in 


1 


122  HEAD  AND  NECK 

each  eyelid,  sweep  in  gentle  curves  from  the  medial  palpebral 
ligament  to  the  lateral  palpebral  raphe,  gaining  attachment  to 
both.  They  form  a  continuous  layer  of  uniform  thickness  in 
each  eyelid,  except  near  the  free  margins,  where,  close  to  the 
bases  of  the  eyelashes,  there  is  a  more  pronounced  fasciculus 
termed  the  ciliary  bundle. 

The  orbital  portion  of  the  muscle  passes  upwards  to  the 
forehead,  laterally  to  the  temporal  region  and  downwards  into 
the  cheek.  Its  fibres  are  relatively  dark  and  coarse.  They 
all  take  origin  medially  from  the  medial  part  of  the  palpebral 
ligament,  the  medial  angular  process  of  the  frontal  bone,  and 
the  frontal  process  of  the  maxilla,  and  they  sweep  laterally 
round  the  margin  of  the  orbit  in  the  form  of  a  series  of  con- 
centric loops.  The  pars  lacrimalis  of  the  orbicularis  oculi 
(O.T.  tensor  tarsi)  will  be  described  when  the  eyelids  are 
dissected  (p.  140). 

Musculus  Epicranius  (O.T.  Occipito  -  Frontalis).  —  The 
epicranius  is  a  quadricipital  muscle  possessing  two  occipital 
heads,  the  occipitales  muscles,  and  two  frontal  heads,  the 
frontales  muscles ;  they  are  all  inserted  into  an  intermediate 
aponeurosis,  the  galea  aponeurotica  (O.T.  epicranial  aponeur- 
osis)^ which  extends  from  the  frontal  to  the  occipital  region 
(p.  158).  The  lower  part  of  each  frontal  head  blends  with  the 
orbicularis  oculi,  and  from  its  medial  border  a  small  muscular 
bundle,  known  as  the  ?nusculus  procerus  (O.T.  pyrafnidalis 
nasi\  descends  to  the  dorsum  of  the  nose.  At  present  only 
the  frontaUs  and  the  procerus  are  to  be  displayed. 

The  Frontalis  becomes  apparent  immediately  above  the 
upper  border  of  the  orbicularis  oculi.  As  it  is  cleaned  care 
should  be  taken  to  avoid  injury  to  the  branches  of  the  supra- 
orbital nerve  which  pierce  it.  It  has  little  or  no  attachment 
to  bone.  Below,  its  fibres  either  blend  with  the  fibres  of  the 
orbicularis  oculi  or  they  are  attached  to  the  skin  of  the  eye- 
brows. Above,  they  terminate  in  the  galea  aponeurotica  in  the 
region  of  the  coronal  suture.  The  lateral  border  is  attached 
to  the  temporal  ridge  by  aponeurotic  fibres,  and  the  medial 
border  blends  with  its  fellow  of  the  opposite  side  for  a  short 
distance  above  the  root  of  the  nose.  Above  the  union  the 
medial  fibres  of  opposite  sides  diverge,  and  below  it  they  pass 
downwards  over  the  nasal  bones  as  the  proceral  muscles. 

Musculus  Procerus  (O.T.  Pyramidalis  Nasi). — The  proceral 
muscles  are  often  absent;  when  present,  each  springs  from 


FACE  x\ND  FRONTAL  REGION  OF  HEAD     123 

the  lower  and  medial  part  of  the  corresponding  frontalis. 
It  descends  over  the  nasal  bone  and  ends  on  the  dorsum 
of  the  nose,  where  some  of  its  fibres  blend  with  the  trans- 
verse part  of  the  nasalis  and  others  are  inserted  into  the  skin. 

Along  the  lower  and  medial  border  of  the  orbicularis  oculi 
will  be  found  the  muscles  of  the  nose  and  the  upper  lip. 

The  proper  muscles  of  the  nose  are  the  musculus  nasalis 
and  the  musculus  depressor  septi,  but  the  procerus  may  also 
be  looked  upon  as  partly  a  nasal  muscle,  and  the  angular 
head  of  the  quadratus  labii  superioris  has  a  nasal  attachment. 

Musculus  Nasalis. — The  musculus  nasaUs  consists  of  two 
parts,  the  pars  transversa  (O.T.  co?7ipressor  ?iaris),  and  the 
pars  alaris  (O.T.  dilator  ?taris).  The  pars  transversa  springs 
from  the  root  of  the  frontal  process  of  the  maxilla,  passes 
across  the  cartilaginous  part  of  the  nose,  above  the  ala,  and 
ends  in  an  aponeurosis  which  connects  it  with  its  fellow  of 
the  opposite  side.  The  pars  alaris  springs  from  the  maxilla, 
at  the  side  of  the  lower  part  of  the  anterior  nasal  aperture, 
and  it  terminates  in  the  posterior  part  of  the  ala  and  the 
mobile  part  of  the  septum  of  the  nose.  The  nasalis  is  partly 
concealed  by  the  medial  fibres  of  the  quadratus  labii  superioris. 

Musculus  Depressor  Septi  Nasi. — This  small  muscle  is 
frequently  difficult  to  display.  It  springs  from  the  superficial 
fibres  of  the  upper  part  of  the  orbicularis  oris,  and  is  inserted 
into  the  anterior  part  of  the  septum  of  the  nose.  It  depresses 
the  septum  and  reduces  the  anteroposterior  diameter  of  the 
anterior  nasal  aperture. 

After  the  muscles  of  the  nose  have  been  examined  clean 
the  superficial  muscles  of  the  mouth  and  cheek. 

The  Muscles  of  the  Mouth  and  Cheeks. — The  muscles  of 
this  group  form  two  layers,  a  superficial  and  a  deep.  Those 
of  the  superficial  group  are  the  orbicularis  oris,  quadratus 
labii  superioris,  zygomaticus,  triangularis,  risorius,  quadratus 
labii  inferioris ;  those  of  the  deeper  group  are  the  buccinator, 
caninus,  incisivi  and  mentalis.  x\ll,  with  the  exception  of  the 
orbicularis  oris,  are  bilateral.  The  members  of  the  superficial 
group  must  be  examined  first ;  the  deeper  muscles  will  be 
displayed  after  the  superficial  vessels  and  nerves  have  been 
dissected. 

Orbicularis  Oris. — The  orbicularis  oris  is  the  sphincter 
muscle  of  the  oral  aperture.  It  lies  in  the  substance  of  the 
lips,  and  consists  of  a  deeper  layer  of  fibres  which  are  arranged 


124 


HEAD  AND  NECK 


in  concentric  ellipsoidal  rings,  and  a  series  of  superficial  fibres 
into  which  all  the  other  muscles  of  the  lips  and  cheeks  con- 
verge. The  details  of  its  formation  cannot  be  understood 
until  the  attachments  of  the  other  muscles  have  been  studied. 


Frontalis 


Orbicularis  oculi 


Procerus 


M.  quadratus  labil  superioris 
angular  head 

M.  nasalis  pars  transversa 

M.  quadratus  labii  superioris 
infra-orbital  head 


M.  zygomaticub 


M.  caninu 


Risorius 


Orbicularis  oris 


Orbicularis  oris 


quadratus  labii  inferioris 


^         Platysma 

Fig.  57. — The  Facial  Muscles. 

Musculus  Quadratus  Labii  Superioris. — The  quadratus 
labii  superioris  possesses  three  heads — a  zygomatic,  an  infra- 
orbital, and  an  angular.  As  the  muscle  is  cleaned  the 
dissector  should  secure  the  upper  part  of  the  anterior  facial 
vein,  which  crosses  its  superficial  surface. 


FACE  AND  FRONTAL  REGION   OF  HEAD     125 

The  zygomatic  head  (O.T.  zygomaticiis  minor)  springs 
from  the  anterior  part  of  the  facial  surface  of  the  zygomatic 
bone,  under  cover  of  the  lower  lateral  part  of  the  orbicularis 
oculi.  It  runs  downwards  and  anteriorly,  and  is  inserted  into 
the  lateral  part  of  the  upper  portion  of  the  orbicularis  oris 
and  into  the  adjacent  part  of  the  skin  of  the  upper  lip. 

TJu  Infra-orbital  Head  (O.T.  Levator  Labii  Superior  is 
Proprius). — This  head  springs  from  the  whole  length  of  the 
infra-orbital  border,  under  cover  of  the  orbicularis  oculi.  It 
is  inserted  into  the  upper  lateral  part  of  the  orbicularis  oris 
and  the  skin  of  the  upper  lip. 

The  angular  head  (O.T.  levator  labii  superioris  alcEque 
nasi)  springs  from  the  frontal  process  of  the  maxilla.  It 
broadens  as  it  descends,,  and  it  is  inserted  into  the  ala  of  the 
nose  and  into  the  upper  part  of  the  orbicularis  oris. 

Musculus  Zygomaticus. — The  zygomaticus  (O.T.  zygo- 
maticus  major)  is  a  comparatively  long,  slender  muscular 
band  which  springs  from  the  facial  surface  of  the  zygomatic 
bone,  under  cover  of  the  lower  lateral  fibres  of  the  orbicularis 
oculi  and  to  the  lateral  side  of  the  zygomatic  head  of  the 
quadratus  labii  superioris.  Its  fibres  pass  downwards  and 
medially  to  the  angle  of  the  mouth,  where  some  blend  with 
the  orbicularis  oris  and  others  are  inserted  into  the  skin. 

The  Risorius. — This  muscle,  when  well  developed,  consists 
partly  of  some  of  the  uppermost  fibres  of  the  platysma  muscle 
of  the  neck,  which  bend  anteriorly  to  the  angle  of  the  mouth, 
and  partly  of  additional  fibres  which  spring  from  the  fascia 
over  the  masseter  muscle  and  the  parotid  gland.  Both 
groups  of  fibres  blend  with  the  fibres  of  the  orbicularis  oris 
at  the  angle  of  the  mouth. 

Musculus  Triangularis. — The  triangularis  (O.T.  depressor 
anguli  oris)  springs  from  the  oblique  line  on  the  lateral  surface 
of  the  body  of  the  mandible.  Its  fibres  converge  as  they 
pass  anteriorly  and  upwards,  and,  at  the  angle  of  the  mouth, 
they  blend  with  the  orbicularis  oris,  in  which  some  of  them 
curve  past  the  angle  and  terminate  in  the  substance  of  the 
upper  lip  (Figs.  57,  58). 

Musculus  Quadratus  Labii  Inferioris  (O.T.  Depressor  Labii 
Inferioris). — This  muscle  springs  from  the  lower  part  of  the 
superficial  surface  of  the  mandible,  between  the  mental 
tubercle  and  the  mental  foramen,  its  posterior  border  being 
overlapped   by   the    triangularis.      The  fibres    pass   upwards 


126 


HEAD  AND  NECK 


and  medially,  some  to  blend  with  the  orbicularis  oris  and 
others  to  gain  attachment  to  the  skin  of  the  lower  lip. 
'  Platysma. — Only  the  upper  part  of  the  broad,  flat, 
quadrangular  subcutaneous  muscle  of  the  neck  is  at  present 
visible.  The  posterior  fibres  ascend  over  the  lower  border 
of  the  ramus  and  the  posterior  part  of  the  lower  border  of 
the  body  of  the  mandible,  and  they  have  already  been  seen 
taking  part  in  the  formation  of  the  risorius.  The  anterior 
fibres  gain  direct  insertion  into  the  anterior  part  of  the  lower 

M.  quadratus  labii  superloris 
caput  angulare 


M.  quadratus  labii 
superioris  caput 
infraorbitale 


M.  caninus 


M.  triangularis 


M.  quadratus  labii  inferioris 


Fig.  58. — Diagram  of  the  Orbicularis  Oris  Muscle. 
The  fibres  which  enter  it  from  the  buccinator  are  not  represented. 

border  of  the  body  of  the  mandible.  The  latter  attach- 
ment is  the  only  bony  attachment  which  the  muscle  possesses, 
all  its  other  attachments  being  either  to  fascia  or  to  skin. 

Dissection. — Cut  through  the  posterior  half  of  the  platysma  along  the 
lower  border  of  the  mandible ;  detach  the  risorius  from  the  fascia  on 
the  masseter  ;  then  turn  the  risorius  and  the  detached  part  of  the  platysma 
towards  the  angle  of  the  mouth.  Whilst  doing  this  be  careful  to  avoid 
injuring  the  branches  of  the  vessels  and  nerves  of  the  face. 

As  soon  as  the  platysma  and  the  risorius  are  reflected  search  below  the  level 
of  the  ear  for  branches  of  the  great  auricular  nerve  which  ascend  over  the 
lower  part  of  the  parotid  gland.  Some  of  them  pierce  the  parotid  and 
terminate  in  its  substance,  others  end  in  the  skin  of  the  masseteric  region. 

Find  the  anterior  facial  vein  and  the  external  maxillary  artery  at  the 


FACE  AND   FRONTAL  REGION  OF   HEAD     127 

lower  and  anterior  angle  of  the  masseter  as  they  cross  the  lower  border  of 
the  mandible.  Clean  them  at  this  point,  but  do  not  trace  them  towards 
their  terminations  at  present. 

At  the  posterior  border  of  the  mandible  note  the  fascia  over  the  super- 
ficial surface  of  the  parotid  gland.  It  ascends  from  the  fascia  of  the  neck, 
and  is  attached  above  to  the  zygomatic  arch.  Note  also  that  at  the  anterior 
border  of  the  parotid  this  fascia  blends  with  the  fascia  on  the  superficial 
surface  of  the  masseter  muscle.  Cut  through  the  fascia  covering  the 
parotid  gland  immediately  anterior  to  the  ear,  extending  the  incision  from 
the  zygoma  above  to  the  angle  of  the  mandible  below  ;  then  raise  the 
fascia  from  the  gland,  dissecting  carefully  anteriorly,  upwards,  and  down- 
wards. As  the  extremities  and  the  anterior  border  of  the  gland  are 
approached,  look  carefully  for  nerves  and  vessels  which  emerge  from 
beneath  them,  and  also  for  the  duct  of  the  gland,  which  appears  from 
under  cover  of  the  anterior  border  about  a  finger's  breadth  below  the 
zygoma.  The  duct  has  thick  walls,  is  of  considerable  size,  and  is  easily  re- 
cognised. It  runs  anteriorly  across  the  masseter  and  turns  round  the  anterior 
border  of  the  muscle,  bending  at  right  angles  to  its  original  course.  It 
pierces,  in  turn,  the  fascia  covering  the  buccinator  muscle,  the  buccinator 
muscle  itself  and  the  mucous  membrane  of  the  mouth  ;  and  it  opens  into 
the  vestibule  of  the  mouth,  on  a  small  papilla  opposite  the  second  molar 
tooth  of  the  maxilla.  Above  the  duct  and  below  the  zygomatic  arch  find 
(i)  the  accessory  parotid,  a  small  detached  part  of  the  parotid  which 
lies  a  short  distance  anterior  to  the  anterior  border  of  the  main  mass 
of  the  gland  ;  (2)  the  transverse  facial  vessels  ;  and  (3)  the  zygomatic 
branches  of  the  facial  nerve.  Below  the  duct  find  the  buccal  and  the 
mandibular  branches  of  the  facial  nerve.  At  the  upper  end  of  the  parotid 
seek  for  the  superficial  temporal  vessels.  Posterior  to  them  lies  the  auriculo- 
temporal branch  of  the  third  division  of  the  trigeminal  nerve,  and  an- 
terior to  them,  the  temporal  branches  of  the  facial  nerve.  From,  or  from 
beneath,  the  lower  extremity  of  the  gland  emerge  (i)  the  cervical  branch  of 
the  facial  nerve,  (2)  the  posterior  facial  vein  (O.T.  anterior  division  of  the 
temporo-maxillary  vein),  and  (3)  the  external  jugular  vein. 

The  Terminal  Branches  of  the  Facial  Nerve. — The  dis- 
sector should  note  that  there  are  five  terminal  branches,  or 
groups  of  branches,  of  the  facial  nerve:  (i)  temporal;  (2) 
zygomatic;  (3)  buccal;  (4)  mandibular;  (5)  cervical.  They 
all  emerge  from  under  cover  of  the  parotid  gland,  the 
temporal  branches  at  its  upper  end,  the  cervical  at  its  lower 
end,  and  the  remaining  three  groups  of  branches  at  its 
anterior  border.  The  temporal  branches  will  be  followed 
when  the  temporal  region  and  the  scalp  are  being  dissected, 
and  the  cervical  branch  when  the  anterior  triangle  of  the  neck 
is  displayed ;  but  the  remaining  three  groups  of  branches 
should  now  be  followed  to  their  terminations. 

The  upper  filaments  of  the  zygomatic  branch  or-  bra?2ches  run 
anteriorly,  across  the  zygomatic  bone,  and  terminate,  in  both 
the  upper  and  the  lower  eyelid,  in  the  fibres  of  the  orbi- 
cularis oculi.  If  the  branches  are  carefully  traced,  one  of 
them   will  be   found    to   communicate  with    the    zygomatico- 


128 


HEAD  AND  NECK 


facial  branch  of  the  second  or  maxillary  division  of  the  fifth 
nerve.  This  small  nerve  pierces  the  zygomatic  bone  a  short 
distance  below  the  lateral  border  of  the  orbit. 

The  lower  filaments  are  larger.  They  run  anteriorly  along 
the  lower  border  of  the  zygomatic  arch,  under  cover  of  the 
musculus    zygomaticus    and    the    infra-orbital    part    of    the 

Supra-orbital 

Zygomat  ico -temporal 
Y^Supra-trochlear 
Lacrimal 


Infra-trochlear 
, — External  nasal 
Infra-orbital 


Mental 


Zygomatico- 
facial 


^uriculo-temporal 


Posterior  auricular 


Trunk  of  facial 

Branch  to  posterior 

belly  of  digastric 

and  stylo-hyoid 


Buccinator 


Fig.  59- — Nerves  of  the  Face.      The  facial  nerve  is  depicted  in  yellow, 
the  sensory  branches  of  the  trigeminal  in  black, 

I.  Temporal  branches.  4.   Buccal  branch. 

2  and  3.  Zygomatic  branches.  5.   Mandibular  branch. 

6.  Cervical  branch. 

quadratus  labii  superioris,  and  deep  to  the  latter  they  com- 
municate with  the  infra-orbital  branch  of  the  maxillary  division 
of  the  fifth  nerve,  forming  with  it  the  i7ifra-07'bital plexus. 

The  buccal  branch  or  branchts  run  towards  the  angle  of 
the  mouth.  At  the  anterior  border  of  the  masseter  they  com- 
municate, around  the  anterior  facial  vein,  with  the  buccinator 
branch  (O.T.  jlong  buccal)  of  the  third  division  of  the  fifth, 
and  they  supply  the  buccinator  and  the  orbicularis  oris. 

Dissection. — ^In  order  to  trace  the  branches  to  their  terminations  and  to 
display  fully  the  infra-orbital  plexus,  cut  through  the  musculus  zygomaticus 


FACE  AND   FRONTAL  REGION  OF   HEAD     129 

and  the  quadratus  lahii  superioris  immediately  below  their  origins,  and 
turn  them  downwards  towards  the  upper  lip.  When  this  has  been  done, 
clear  away  the  fatty  tissue  which  lies  on  the  deep  aspect  of  the  quadratus 
labii  superioris  and  secure  the  infra-orbital  vessels  and  nerve,  as  they  emerge 
from  the  infra-orbital  foramen.  The  infra-orbital  plexus  lies  deep  to  the 
quadratus  labii  superioris,  and  on  the  superficial  aspect  of  the  musculus 
caninus.  From  the  plexus  three  groups  of  branches  are  distributed  :  (i) 
palpebral,  which  pass  upwards  to  the  lower  eyelid  ;  (2)  nasal,  which  run 
medially  to  the  nose  ;  and  (3)  labial,  which  descend  to  the  upper  lip.  Either 
by  means  of  these  branches,  or. more  directly,  the  lower  zygomatic  twigs 
of  the  facial  nerve  are  distributed  to  the  musculus  zygomaticus,  the  muscles 
of  the  lower  eyelid,  muscles  of  the  nose,  and  the  muscles  of  the  upper  lip. 

The  mandibular  branch  or  branches  run  anteriorly  along  the 
mandible  to  be  distributed  to  the  muscles  of  the  lower  lip. 
As  they  pass  anteriorly  they  lie  deep  to  the  triangularis,  and 
they  communicate,  under  cover  of  it,  with  the  mental  branch 
of  the  inferior  alveolar  (O.T.  dental)  nerve.  To  display  this 
communication  the  triangularis  must  be  reflected,  and  the 
mental  vessels  and  nerves  must  be  found  as  they  emerge 
from  the  mental  foramen. 

Arteria  Maxillaris  Externa  (O.T.  Facial).  —  The  ex- 
ternal maxillary  artery  is  a  tortuous  vessel  which  enters  the 
face  at  the  lower  and  anterior  angle  of  the  masseter,  after 
turning  round  the  lower  border  of  the  mandible  and  piercing 
the  deep  fascia  of  the  neck.  From  that  point  it  runs 
anteriorly  and  upwards  to  the  angle  of  the  mouth  and  then, 
assuming  a  more  vertical  direction,  it  is  prolonged  upwards, 
as  the  angular  artery,  to  the  medial  commissure  of  the 
eyelids,  in  the  substance  of  the  angular  head  of  the  quadratus 
labii  superioris.  Immediately  after  its  entrance  into  the  face 
it  is  comparatively  superficial,  being  covered  by  skin,  super- 
ficial fascia,  and  platysma,  and  it  is  easily  compressed  against 
the  bone.  More  anteriorly  it  lies  between  the  zygomaticus 
superficially  and  the  buccinator  deeply,  then  between  the 
quadratus  labii  superioris  and  the  caninus,  and,  as  already 
stated,  its  terminal  part  is  usually  embedded  in  the  substance 
of  the  quadratus  labii  superioris. 

Branches. — The  branches  of  the  external  maxillary  artery 
form  two  groups,  a  posterior  and  an  anterior.  The  branches 
of  the  posterior  group  pass  posteriorly  and  are  of  small  size. 
They  are  distributed  to  the  masseteric,  buccal,  and  malar 
regions  where  they  anastomose  with  the  transverse  facial,  the 
buccinator,  and  the  infra-orbital  arteries. 

The  branches  of  the  anterior  group  run  anteriorly  and  re- 

VOL.    II — 9 


I30 


HEAD  AND  NECK 


ceive  special  names  :   they  are  the  inferior  labial,  the  superior 
labial,  the  lateral  nasal,  and  the  angular  continuation. 

The  ijiferior  labial  (O.T.  inferior  coronary)  arises  below  the 
level   of  the   angle   of   the  mouth    and    passes   towards   the 


Superficial  temporal 


Frontal  branch  of 
ophthalmic  artery 
Supra-orbital  branch  of 
ophthalmic  artery 


Middle  temporal 
Transverse  facial 

Angular 
Lateral  nasal 


Infra-orbital 
Superior  labial 


S®^)^  Inferior  labial 

A    -,^  ^^J  inferior 

labial.)     See  p.  131 


i'luccinator  branch  of  internal  maxillary 
External  maxillary 
Fig.  60.  — Arteries  of  the  Face. 

median  plane,  under  cover  of  the  triangularis,  the  quadratus 
labii  inferioris,  and  the  orbicularis  oris.  In  the  substance  of 
the  lip  it  lies  immediately  adjacent  to  the  mucous  membrane, 
and  it  anastomoses  in  the  median  plane  with  its  fellow  of  the 
opposite  side. 

The  superior  labial  arises   about  the   level   of   the   angle 


FACE  AND   FRONTAL  REGION  OF  HEAD     131 

of  the  mouth  and  runs  medially  in  the  upper  lip,  between 
the  orbicularis  oris  and  the  mucous  membrane.  Before  it 
anastomoses  with  its  fellow  of  the  opposite  side,  it  gives  off 
a  branch,  the  septal  artery  of  the  nose,  which  passes  upwards 
and  ramifies  on  the  lower  and  anterior  part  of  the  nasal  septum, 
where  it  anastomoses  with  the  septal  branch  of  the  spheno- 
palatine artery. 

The  Angular  Artery. — This  is  the  continuation  of  the 
external  maxillary  beyond  the  point  of  origin  of  the  lateral 
nasal  branch.  It  runs  upwards  in  the  substance  of  the 
angular  head  of  the  quadratus  labii  superioris,  and  it 
terminates  at  the  medial  commissure  of  the  eye  by  anastomos- 
ing with  the  nasal  branch  of  the  ophthalmic.  The  lateral 
?iasal  branch  springs  from  the  external  maxillary  at  the  point 
where  it  becomes  the  angular.  It  ramifies  on  the  side  of  the 
nose  and  anastomoses  in  the  median  plane  with  its  fellow  of 
the  opposite  side. 

In  addition  to  the  branches  already  noted,  a  very  definite 
branch  is  usually  given  off  from  the  anterior  aspect  of  the 
external  maxillary  artery  immediately  after  it  crosses  the 
lower  border  of  the  mandible.  This  branch  (O.T.  inferior 
labial)  runs  towards  the  median  plane  under  cover  of  the 
triangularis  and  the  depressor  labii  inferioris,  and  it  anasto- 
moses not  only  with  the  inferior  labial  (O.T.  inferior  coronary) 
above,  and  its  fellow^  of  the  opposite  side  in  the  median  plane, 
but  also  with  the  mental  branch  of  the  inferior  alveolar  artery. 

Vena  Facialis  Anterior  (O.T.  Facial). — The  anterior 
facial  vein  is  a  less  tortuous  vessel  than  the  external  maxillary 
artery  to  w4iich  it  corresponds,  and  it  lies  posterior,  and  on 
a  slightly  more  superficial  plane.  •  It  commences  as  the 
a?igular  vein,  which  is  formed  at  the  medial  commissure 
of  the  eyelids,  by  the  union  of  the  frontal  and  supra-orbital 
veins,  which  descend  from  the  forehead.  It  passes  down- 
wards and  posteriorly,  in  a  comparatively  straight  line,  to  the 
anterior  inferior  angle  of  the  masseter,  which  it  crosses 
immediately  behind  the  external  maxillary  artery;  then  it 
pierces  the  deep  fascia  of  the  neck,  and  enters  the  sub- 
maxillary triangle.  In  the  upper  part  of  the  face  it  lies  on 
the  quadratus  labii  superioris ;  then  it  is  situated  between  the 
zygomaticus  and  the  risorius  superficially  and  the  buccinator 
deeply ;  and  as  it  crosses  the  anterior  angle  of  the  masseter 
it  is  covered  with  the  skin,  superficial  fascia,  and  the  platysma, 
II — 9  a 


132  HEAD  AND  NECK 

Tributaries. — In  addition  to  the  frontal  and  supra-orbital 
veins,  it  receives  external  nasal,  palpebral,  superior  liabial, 
inferior  labial,  masseteric  and  superficial  parotid  tributaries. 
As  it  crosses  the  buccinator  muscle  it  is  joined  by  the  deep 
facial  vein,  which  connects  it  with  the  pterygoid  plexus  of 
veins  in  the  infra-temporal  region. 

Dissection. — After  the  branches  of  the  facial  nerve,  the  external  maxillary 
artery  and  the  anterior  facial  vein  have  been  studied,  the  dissection  of  the 
deeper  muscles  and  the  deeper  vessels  and  nerves  must  be  proceeded  with ; 
but  the  supra-orbital  and  supra-trochlear  nerves,  the  supra-orbital  vessels, 
and  >the  corrugator  supercilii  muscle  may  be  left  till  the  scalp  is  dissected 
(p.  156). 

Musculus    Caninus    (O.T.  Levator  Anguli   Oris). — The 

caninus  is  concealed  by  the  lower  part  of  the  orbicularis 
oculi,  the  quadratus  labii  superioris,  and  the  zygomaticus,  and 
it  is  crossed  superficially,  near  the  angle  of  the  mouth,  by 
the  external  maxillary  artery.  When  the  structures  superficial 
to  it  are  turned  aside,  the  muscle  will  be  found  springing  from 
the  canine  fossa  below  the  infra-orbital  foramen.  It  passes 
downwards  to  the  angle  of  the  mouth,  where  it  blends  with  the 
orbicularis  oris,  some  of  its  fibres  passing  into  the  lower  lip 
(Fig.  57).     It  is  an  elevator  of  the  angle  of  the  mouth. 

The  Buccinator.  —  This  muscle  occupies  the  interval 
between  the  upper  and  the  lower  jaws  and  forms  a  most 
important  part  of  the  substance  of  the  cheek.  Above,  it 
springs  from  the  alveolar  border  of  the  maxilla,  in  the 
region  of  the  molar  teeth.  Below,  it  arises  from  the 
alveolar  border  of  the  mandible,  also  in  the  region  of  the 
molar  teeth,  and,  posteriorly,  it  is  attached  to  the  pterygo- 
mandibular raphe,  which  forms  a  bond  of  union  between 
the  buccinator  and  the  superior  constrictor  of  the  pharynx. 
This  attachment  will  be  seen  to  better  advantage  when  the 
wall  of  the  pharynx  is  studied  (p.  373).  Anteriorly,  its  fibres 
converge  towards  the  angle  of  the  mouth,  where  they  blend 
with  the  orbicularis  oris,  of  which  they  form  a  large  part. 
The  manner  in  which  the  fibres  enter  the  orbicularis  must  be 
carefully  noted.  The  upper  and  lower  fibres  pass  directly 
to  the  corresponding  lips  ;  the  middle  fibres,  on  the  other 
hand,  decussate  at  the  angle  of  the  mouth,  so  that  the  lower 
fibres  of  the  series  enter  the  upper  lip,  whilst  the  higher 
fasciculi  reach  the  lower  lip  (Fig.  61). 

The  Molar  Glands. — The  buccinator  is  covered  posteriorly 


FACE  AND  FRONTAL  REGION   OF   HEAD     133 

by  a  pad  of  fat,  the  suctorial  pad,  and  by  a  strong  layer  of 
fascia  which  must  be  carefully  removed.  As  this  is  being 
done  the  dissector  will  find;  both  superficial  and  deep  to 
the  fascia,  a  number  of  small  glands,  the  molar  salivary 
glands.  The  ducts  of  these  glands  pierce  the  buccinator  and 
open  into  the  vestibule  of  the  mouth.  One  or  two  buccal 
lymph  gkmds  also  are  sometimes  found  resting  on  the  super- 
ficial surface  of  the  buccinator. 

Dissection. — After  the  dissection  of  the  buccinator  and  the  molar  glands 
is  completed,  remove  the  stitches  from  the  lips  ;  evert  the  lips  and  dissect 
the  mucous  membrane  from  the  deep  surfaces,  in  order  to  expose  the 
muscular  sHps  which  attach  the  orbicularis  oris  to  the  alveolar  margins  of  the 
upper  and  the  lower  jaws,  and  to  display  the  mentalis  muscle.  As  the  lips 
are  everted  the  dissector  should  note  that  a  fold  of  mucous  membrane,  the 
fremduni  iabii,  passes  from  each  lip  to  the  gum  of  the  corresponding  jaw  in 


Fig.  61. — Arrangement  of  the  Fibres  of  the  Buccinator  Muscle 
at  the  Angles  of  the  Mouth. 

the  median  plane  ;  and  as  the  mucous  membrane  is  removed  a  number-'of 
small  labial  salivary  glands,  which  lie  in  the  submucous  tissue,  w^ill  be 
seen.  They  are  readily  felt  in  the  living  subject  by  pressing  the  tip  of  the 
tongue  against  the  inner  surfaces  of  the  lips. 

Musculi  Incisivi  Labii  Superioris  et  Inferioris. — These 
are  four  small  muscular  bundles,  two  upper  and  two  lower, 
which  attach  the  deeper  part  of  the  orbicularis  oris  to  the 
alveolar  margins  of  the  jaws  in  the  regions  of  the  upper  and 
lower  lateral  incisor  teeth. 

Musculus  Mentalis. — When  the  incisive  muscles  of  the 
lower  jaw  are  detached  from  the  bone  and  the  lower  lip 
is  further  everted,  a  distinct  muscular  bundle  will  be  found  on 
each  side,  springing  from  the  outer  surface  of  the  socket  of  the 
canine  tooth,  under  cover  of  the  quadratus  labii  inferioris. 
The  two  bundles  converge  and  blend  together,  between  the 
medial  borders  of  the  musculi  quadrati  labii  inferioris,  to 
form  a  single  bundle  which  is  inserted  into  the  skin  of  the 
chin.  It  is  an  elevator  of  the  skin  of  the  chin. 
II— 9  & 


134 


HEAD  AND  NECK 


Nervus  Buccinatorius  (O.T.  Long  Buccal). — This  nerve  is 
a  branch  of  the  third  division  of  the  trigeminal  nerve.  It 
passes  anteriorly  into  the  cheek  from  under  cover  of  the 
ramus  of  the  mandible.  It  is  a  sensory  nerve,  and  it  supplies 
branches  to  the  skin  on  the  outer  surface  and  the  mucous 
membrane  on  the  inner  surface  of  the  buccinator  muscle. 
In  order  to  display  it  at  the  present  stage  it  may  be  necessary 
to  make  an  antero-posterior  incision  through  the  middle  of 
the  anterior  border  of  the  masseter. 

Eyelids. — The  following  strata  will  be  exposed  in  each 
eyelid  as  the  dissection  is  carried  from  the  surface  towards 
the  conjunctiva. 


Upper  Lid. 

Lower  Lid. 

I.    Integument. 

I. 

Integument. 

2.   Palpebral  part  of  the  orbicularis 

2. 

Palpebral  part  of  the  orbicularis 

oculi. 

oculi. 

3.   The      tarsus,      the      palpebral 
fascia,  and  the  expanded  ten- 

•3- 

The   tarsus    and   the   palpebral 
fascia. 

don    of  the    levator  palpebroe 

supenoris. 
4.   Conjunctiva. 

4- 

Conjunctiva. 

In  addition  to  these  structures,  two  ligamentous  bands, 
named  the  medial  palpebral  ligament  (O.T.  internal  tarsal 
ligament)  and  the  lateral  palpebral  raphe  (O.T.  external 
tarsal  ligament),  will  be  noticed.  They  attach  the  tarsi  to 
the  medial  and  lateral  margins  of  the  orbit. 

Integument  and  Orbicularis  Oculi. — These  strata  have 
been  examined  already,  and  the  skin  has  been  reflected. 

Dissedioit. — Separate  the  palpebral  part  of  the  orbicularis  oculi  from  the 
remainder  by  a  circular  incision  ;  turn  the  palpebral  part  towards  the 
rima  palpebrarum,  and  take  care,  whilst  raising  the  muscle  fibres,  to  preserve 
the  palpebral  vessels  and  nerves,  and  at  the  same  time  to  avoid  injury  to 
the  palpebral  fascia.  As  the  dissection  is  completed  the  origin  of  the 
muscle  from  the  medial  palpebral  ligament  (p.  121)  will  be  displayed. 

Tarsi. — The  removal  of  the  palpebral  part  of  the  orbicularis 
oculi  brings  into  view  the  palpebral  fascia  and  the  tarsi. 
These  lie  in  the  same  morphological  plane,  and  they  constitute 
the  ground-work  of  the  eyelids. 

The  tarsi  are  two  thin  plates  of  condensed  fibrous  tissue, 
placed  one  in  each  eyelid  so  as  to  occupy  an  area  immediately 


FACE  AND  FRONTAL  REGION  OF  HEAD     135 

adjoining  its  free  margin.  They  differ  very  materially  from 
each  other.  The  superior  tarsal  plate  is  much  the  larger  of 
the  two,  and  presents  the  figure  of  a  half  oval.  Its  deep 
surface  is  intimately  connected  with  the  subjacent  conjunctiva, 
whilst  its  superficial  surface  is  clothed  by  the  orbicularis  muscle, 
and  is  in  relation  to  the  roots  of  the  eyelashes.  Its  superior 
border  is  thin,  convex,  and  continuous  with  a  tendinous 
expansion  of  the  levator  palpebrae  superioris.  The  inferior 
border  of  the  tarsal  plate  is  thickened  and  straight,  and  the 
integument  adheres  firmly  to  it. 

The  inferior  tarsal  plate  is  a  narrow  strip  which  is  similarly 
placed  in  the  lower  lid. 

Glandulae  Tarsales  (O.T.  Meibomian  Follicles). — At  this 
stage  the  student  should  examine  the  tarsal  glands,  which  he 
will  display  by  everting  the  eyelids.  They  are  placed  on  the 
deep  surfaces  of  the  tarsi.  To  the  naked  eye  they  appear 
as  closely  placed,  parallel,  yellow  granular -looking  streaks, 
which  run  at  right  angles  to  the  free  margins  of  the  lids. 
They  are  more  numerous  and  of  greater  length  in  the 
upper  lid,  and,  being  lodged  in  furrows  on  the  deep  surface 
of  the  tarsal  plates,  they  are  distinctly  visible  upon  both 
aspects  of  these,  even  while  the  conjunctiva  is  in  position. 
Their  ducts  open  upon  the  free  margin  of  each  lid  posterior 
to  the  eyelashes. 

The  Palpebral  Fascia. — The  palpebral  fascia  is  a  sheet  of 
fibrous  membrane  which  occupies  the  interval  between  the 
tarsi  and  the  margins  of  the  orbit,  forming,  with  the  tarsi,  a 
septum  between  the  orbit  and  the  exterior.  Its  peripheral 
border  is  attached  to  the  orbital  margin,  except  at  the  medial 
angle  of  the  orbit,  where  it  occupies  a  more  posterior  plane, 
and  is  attached  to  the  crista  lacrimalis,  posterior  to  the  medial 
palpebral  ligament  and  the  lacrimal  sac.  Its  central  border 
in  the  lower  lid  is  connected  with  the  lower  border  of  the 
lower  tarsus.  In  the  upper  lid  it  blends  with  the  expanded 
tendon  of  the  levator  palpebrae  superioris,  and  is  attached 
with  it  to  the  anterior  surface  of  the  upper  tarsus.  It  is 
pierced  by  the  supra-orbital,  supra-trochlear,  and  lacrimal 
branches  of  the  first  division  of  the  trigeminal  nerve,  and 
by  the  terminal  branches  of  the  ophthalmic  artery. 

Raphe  Palpebralis  Lateralis. — The  lateral  palpebral  raphe 
(O.T.  external  tarsal  ligament)  is  merely  a  thickening  of  the 
palpebral  fascia,  between  the  lateral  commissure  and  the 
II— 9  c 


136 


HEAD  AND  NECK 


medial  border  of  the  fronto-sphenoidal  process  of  the  zygomatic 
bone  (O.T.  malar),  to  which  it  connects  both  the  tarsi. 

Ligamentum  Palpebrale  Mediale  (O.T.  Internal  Tarsal 
Ligame?if). — The  medial  palpebral  ligament  is  a  strong  fibrous 
band  which  connects  the  medial  ends  of  both  tarsi  to  the 
frontal  process  of  the  maxilla.  It  lies  between  the  skin 
anteriorly,  and  the  lacrimal  sac  posteriorly.  By  its  upper  and 
lower  borders  it  gives  attachment  to  fibres  of  the  orbicularis 


Tendon  of  levator 
palpebrae  superioris 


Palpebral  fascia 

Palpebral  branch  of \ 

lacrimal  nerve 


Superior  tarsus 

Raphe  palpebralis 
lateralis 


Palpebral  fascia 


Supra-orbital  nerve 
Supra-trochlear  nerve 
Superciliary  arch 

Infra-trochlear  nerve 

Lacrimal  sac 

!__]_  Ligamentum  palpe- 
bral mediale 

Inferior  tarsus 


Infra-orbital  nerve 


Fig.  62. — Dissection  of  the  Right  Eyehd.     The  orbicularis  palpebrarum  has 
been  completely  removed. 

oculi,  and  by  the  lateral  part  of  its  posterior  surface,  to  the 
pars  lacrimalis  of  the  orbicularis  oculi  (O.T.  tensor  tarsi). 

Levator  Palpebrae  Superioris. — Only  the  anterior  expanded 
tendon  of  this  muscle  can  be  seen  at  the  present  stage  of  the 
dissection,  and  that,  as  a  rule,  in  only  a  partially  satisfactory 
manner.  The  muscle  arises  within  the  orbital  cavity,  extends 
forwards  to  the  upper  eyelid,  and  ends  in  an  expanded  tendon 
which  splits  into  three  lamellae ;  a  superior  lamella,  which 
blends  with  the  upper  part  of  the  palpebral  fascia  and  is 
attached  with  it  to  the  anterior  surface  of  the  upper  tarsus; 
an  intermediate  lamella,  which  is  connected  with  the  upper 


FACE  AND  FRONTAL  REGION   OF  HEAD     137 


border  of  the  upper  tarsus;  and  an  inferior  lamella,  which 
gains  insertion  into  the  upper  fornix  of  the  conjunctiva.  It 
raises  the  upper  eyelid  by  pulling  on  the  upper  tarsus,  and  at 
the  same  time  elevates  the  upper  fornix  of  the  conjunctiva. 

Vessels  and  Nerves  of  the  Eyelids. — At  the  medial  com- 
missure two  arteries,  the  palpebral  branches  of  the  ophthalmic, 
pierce  the  palpebral  fascia  and  run  laterally,  one  in  the  upper 
and  one  in  the  lower  lid.  At  the  lateral  margin  of  the 
orbit,  one  or  more  branches  of  the  lacrimal  division  of  the 
ophthalmic  pierce  the  palpebral  fascia  and  anastomose  with 


Frontal  bone 

M.  orbicularis  oculi 


Palpebral  fascia 

Superior  conjunctival  fornix 
Superior  tarsus 

Conjunctival  recess  — Y^- — \ 


Inferior  conjunctival  fornix 
Palpebral  fascia^ 
Fig.  63. — Diagram  of  the  Structure  of  the  EyeHds. 

the  palpebral  arteries.  An  arterial  arch,  arms  iarseus,  is  thus 
formed  close  to  the  margin  of  each  eyelid,  between  the 
orbicularis  muscle  and  the  tarsus. 

The  veins  run  medially  towards  the  root  of  the  nose  and 
open  into  the  frontal  and  angular  veins. 

The  nerves  are  more  numerous  and  come  from  a  number 
of  different  sources.  The  motor  filaments  for  the  various 
parts  of  the  orbicularis  oculi  are  derived  from  the  temporal, 
and  zygomatic  branches  of  the  facial  nerve.  They  enter 
from  the  lateral  margins.  The  sensory  twigs  for  the  upper 
lid  come  from  the  lacrimal,  supra-orbital,  supra-trochlear,  and 
infra-trochlear  branches  of  the  first  or  ophthalmic  division  of 
the  trigeminal  nerve;  and  the  lower  Ud  is  supplied  by  the 


138  HEAD  AND  NECK 

infra-orbital  branch  of  the  second  or  maxillary  division  of  the 
fifth  nerve.  The  lacrimal  nerve  will  be  found  piercing  the 
palpebral  fascia  near  the  lateral  part  of  the  upper  border  of 
the  orbit ;  the  supra-orbital  lies  in  the  supra-orbital  notch  at 
the  junction  of  the  lateral  two-thirds  with  the  medial  third  of 
the  upper  border ;  and  the  supra-  and  infra-trochlear  pierce 
the  palpebral  fascia  at  the  medial  end  of  the  upper  border. 
The  branches  of  the  infra-orbital  nerve  pass  to  the  lower  lid 
in  the  palpebral  branches  of  the  infra-orbital  plexus  (p.  128). 

Apparatus  Lacrimalis. — The  following  structures  are  in- 
cluded under  this  head :  (i)  the  lacrimal  gland  and  its  ducts  ; 
(2)  the  conjunctival  sac ;  (3)  the  puncta  lacrimalia ;  (4)  the 
lacrimal  ducts ;  (5)  the  lacrimal  sac ;  (6)  the  naso-lacrimal 
duct;  (7)  the  lacrimal  part  of  the  orbicularis  oculi. 

Glandula  Lacrimalis. — This  lies  in  the  upper  and  lateral 
part  of  the  orbital  cavity  under  cover  of  the  zygomatic  process 
(O.T.  external  angular)  of  the  frontal  bone.  It  can  be  exposed 
by  cutting  through  the  palpebral  fascia  at  the  upper  and  lateral 
angle  of  the  orbit,  and  it  will  be  found  that  the  anterior  part 
of  the  gland  projects  slightly  beyond  the  orbital  margin  and 
rests  upon  the  conjunctiva  as  the  latter  is  reflected  from  the 
lateral  part  of  the  upper  lid  on  to  the  eyeball.  If  the  anterior 
border  of  the  gland  is  raised  and  the  point  of  the  knife 
carried  carefully  up  and  down  in  the  fascia  under  it,  several 
exceedingly  fine  ducts  will  be  found  passing  from  the  gland 
into  the  lateral  part  of  the  upper  fornix  of  the  conjunctiva. 
The  ducts  vary  in  number,  and  the  secretion  which  they 
convey,  which  constitutes  the  tears,  is  carried,  by  the  in- 
voluntary movements  of  the  upper  eyehd,  over  the  exposed 
surface  of  the  eyeball  and  is  directed  towards  the  medial 
commissure  ;  there  it  passes  through  the  puncta  lacrimalia 
into  the  lacrimal  ducts,  and  is  carried  by  them  to  the  lacrimal 
sac,  whence  it  passes  by  the  naso-lacrimal  duct  into  the 
inferior  meatus  of  the  nose.  Under  ordinary  circumstances, 
the  amount  of  lacrimal  secretion  is  merely  sufficient  for  lubrica- 
tion, and  practically  the  whole  of  it  is  evaporated  from  the 
surface  of  the  eyeball ;  consequently,  when  the  lacrimal  ducts 
and  the  lacrimal  sac  are  extirpated,  a  proceeding  which  is 
necessary  under  certain  circumstances,  the  patient  suffers 
little  or  no  inconvenience  from  the  overflow  of  tears,  so  long 
as  the  secretion  is  not  excessive.  If  the  amount  of  secretion 
is  greater  than  can  be  removed  by  evaporation,  the  excess, 


FACE  AND  FRONTAL  REGION   OF  HEAD     139 

under  ordinary  circumstances,  passes  through  the  pun  eta  into 
the  ducts  and  thence  through  the  lacrimal  sac  and  naso- 
lacrimal duct  to  the  nose ;  and  if  the  secretion  becomes  so 
abundant  that  it  cannot  be  removed  by  evaporation  and 
drainage,  part  flows  through  the  rima  as  tears. 


Lacrimal  gland 

superior  part 

Temporal  muscle 

'emporal  fascia   — 

Excretory  ducts 'V 

Lacrimal  glands', 
lower  part     V 


ifra-orbital  nerve 

Maxillary  sinus  ■^'~" 


Buccinalor 


Conjunctiv^a 
- — T'superior  fornix 

r  Puncta  lacrimalla 
'  Lacrimal  ducts 
Lacrimal  sac 
}iledial  palpebral 
ligament 

■ ^  -Naso-lacrimal  duct 

-]\Iiddle  concha 

~  — '"  INluco-periosteum 
— ^  -  Plica  lacrimalis 

Inferior  meatus 
Liferior  concha 


Fig.  64. — Dissection  of  Lacrimal  Apparatus. 

The  Conjunctival  Sac. — The  conjunctival  sac  is  the  potential 
space  between  the  eyelids  and  the  eyeball.  It  opens  externally 
through  the  rima  and  communicates  with  the  lacrimal  sac 
through  the  puncta  and  the  lacrimal  ducts. 

The  Puncta  Lacrimalla. — It  has  been  noted  already  that 
the  punctum  lacrimale  of  each  hd  lies  at  the  lateral  margin 
of  the  lacus  lacrimalis  (p.  120).      Small  probes  should  now  be 


I40  HEAD  AND  NECK 

passed  through  the  puncta  into  the  lacrimal  ducts  and  along 
the  ducts  into  the  lacrimal  sac  (Fig.  64). 

Saccus  Lacrimalis. — The  lacrimal  sac  is  the  blind  upper 
end  of  a  canal  which  extends  from  the  orbit  to  the  inferior 
meatus  of  the  nose.  It  is  lodged  in  the  fossa  lacrimalis  in 
the  anterior  part  of  the  medial  wall  of  the  orbit.  It  lies 
posterior  to  the  medial  palpebral  ligament,  from  which  it 
receives  a  fibrous  expansion,  and  it  is  covered  on  its  lateral 
aspect,  and  on  the  lateral  part  of  its  posterior  aspect,  by  the  pars 
lacrimalis  of  the  orbicularis  oculi.  The  lacrimal  ducts  open 
into  its  antero- lateral  aspect,  under  cover  of  the  medial 
palpebral  ligament ;  and  it  is  continuous  below  with  the  naso- 
lacrimal duct.  The  anterior  wall  of  the  sac  should  be  incised 
and  a  probe  passed  down  the  naso -lacrimal  duct  into  the 
nose.  Note  that  as  the  probe  passes  along  the  duct  it 
inclines  downwards,  laterally  and  slightly  posteriorly. 

Pars  Lacrimalis  Orbicularis  Oculi  (O.T.  Tensor  Tarsi). — 
This  small  special  portion  of  the  orbicularis  oculi  springs 
from  the  posterior  aspect  of  the  lateral  part  of  the  medial 
palpebral  ligament  and  passes  posteriorly  and  medially,  round 
the  lateral  part  of  the  lacrimal  sac,  to  the  crista  lacrimalis  of 
the  lacrimal  bone,  to  which  it  is  attached.  When  it  contracts 
it  compresses  the  lacrimal  sac,  and  so  tends  to  facilitate  the 
flow  of  the  lacrimal  secretion  into  the  nose. 

Ductus  Naso -Lacrimalis. — This  duct  will  be  seen  at  a 
later  period  of  the  dissection.  It  is  a  bony  canal,  lined  with 
muco-periosteum,  which  runs,  in  the  lateral  wall  of  the  nose, 
from  the  lacrimal  sac  to  the  upper  and  anterior  part  of  the 
inferior  meatus.  It  is  about  half  an  inch  long.  At  the  medial 
side  of  its  lower  end  is  a  fold  of  mucous  membrane,  the  plica 
lacrimalis^  which  serves  as  a  flap  valve  (Fig.  64). 

The  dissection  of  the  face  should  be  completed  by  an 
examination  of  the  nasal  cartilages  and  the  external  nasal 
branch  of  the  ophthalmic  division  of  the  trigeminal  nerve. 
The  nerve  will  be  found  emerging  between  the  lower  border 
of  the  nasal  bone  and  the  lateral  cartilage.  After  its 
emergence  it  descends  to  the  tip  of  the  nose  supplying 
filaments  to  the  skin. 

Dissection.— The  cartilaginous  part  of  the  nose  should  now  be  examined 
by  stripping  off  the  nasalis  muscle  and  the  remains  of  the  integument. 

Nasal    Cartilages. — In    addition    to   the   septal   cartilage, 


FACE  AND  FRONTAL  REGION   OF  HEAD     141 

which  will  be  more  appropriately  studied  in  the  dissection  of 
the  nasal  cavities,  two  cartilaginous  plates  will  be  found 
upon  each  side.     These  are  : — 

1.  The  lateral  cartilage. 

2.  The  cartilage  of  the  ala. 

The  lateral  cartilage  is  a  triangular  plate  which,  by  its 
posterior  margin,  is  attached  to  the  lower  border  of  the 
nasal  bone  and  the  upper  part  of  the  sharp  margin  of  the 
nasal  notch  of  the  maxilla.     In  the  median  plane  this  cartilage 


External  nasal  nerve 
—Lateral  cartilage 


jSIinor  alar  cartilages 
^Nlajor  alar  cartilage 


Fig.  65. — Cartilages  of  the  Nose. 


becomes  continuous  with  its  fellow  of  the  opposite  side,  and 
also  with  the  subjacent  anterior  border  of  the  septal  cartilage 
of  the  nose.  Below,  there  is  a  slight  interval  between  the 
two  lateral  cartilages,  in  which  is  seen  the  margin  of  the 
nasal  septal  cartilage.  The  inferior  border  of  the  lateral 
cartilage  is  connected  with  the  lateral  part  of  the  alar 
cartilage  by  some  dense  fibrous  tissue. 

The  alar  cartilage  is  bent  upon  itself  and  folded  round  the 
orifice  of  the  nostril  anteriorly  and  laterally.  Posteriorly  it 
is  deficient.  The  lateral  part  is  oval,  and  does  not  reach 
down  to  the  margin  of  the  nostril,  nor  posteriorly  as  far 
as  the  nasal  notch  of  the  maxilla.  The  interval  between 
it  and  the  bone  is  filled  in  by  fibrous  tissue  in  which  one  or 
two  small  islands  of  cartilage  (cartilagines  minores  vel  sesa- 
moidese)  appear.  A?iteriorly,  the  bent  part  of  cartilage  comes 
into  contact  with  its  neighbour  and  forms  the  point  of  the 


142  HEAD  AND  NECK 

nose.  Medially^  the  medial  part  of  the  cartilage  is  in  the 
form  of  a  narrow  strip  which  lies  upon  the  lower  part  of  the 
septal  cartilage,  and  projects  slightly  below  it  so  as  to  support 
the  margin  of  the  nostril  upon  this  side.  Its  extremity  is 
turned  slightly  laterally. 


SIDE    OF    THE    NECK. 

On  the  fourth  day  after  the  body  is  brought  into  the  room 
it  is  placed  upon  its  back,  and  the  dissectors  of  the  head  and 
neck  should  examine  the  side  of  the  neck  and  commence  the 
dissection  of  the  posterior  triangle. 

The  side  of  the  neck  is  bounded  below  by  the  clavicle, 
above  by  the  lower  border  of  the  mandible,  the  mastoid 
portion  of  the  temporal  bone,  and  the  superior  nuchal  line  of 
the  occipital  bone.  Anteriorly  it  extends  to  the  median  plane, 
and  posteriorly  to  the  anterior  border  of  the  trapezius  muscle. 
It  is  divided  into  anterior  and  posterior  parts,  the  anterior 
and  posterior  triangles^  by  the  sterno- mastoid  muscle.  If 
the  head  is  pulled  over  towards  the  opposite  side,  the  sterno- 
mastoid  muscle  will  be  seen  descending  from  the  mastoid 
portion  of  the  temporal  bone  and  the  superior  nuchal  line  of 
the  occipital  bone,  to  the  upper  border  of  the  sternal  third 
of  the  clavicle  and  the  anterior  surface  of  the  manubrium 
sterni. 

In  the  lower  part  of  the  posterior  region,  posterior  to  the 
sterno -mastoid  and  above  the  convex  middle  third  of  the 
clavicle,  there  is  a  depression  called  the  fossa  supraclavicularis 
major,  to  distinguish  it  from  the  fossa  supraclavicularis  minor 
which  lies  above  the  sternal  end  of  the  clavicle  between  the 
sternal  and  clavicular  heads  of  the  sterno-mastoid.  The 
brachial  plexus,  the  third  part  of  the  subclavian  artery,  and 
the  supra -clavicular  lymph  glands  lie  in  the  region  of  the 
fossa  supra-clavicularis  major,  and  the  fossa  supra-clavicularis 
minor  indicates  the  position  of  the  internal  jugular  vein  near 
its  lower  end. 

POSTERIOR    TRIANGLE. 

Dissection. — To  expose  the  boundaries  and  contents  of  the  posterior 
triangle  make  the  following  three  incisions  through  the  skin,  (i)  From 
the  back  of  the  auricle  along  the  upper  border  of  the  mastoid  part  of  the 


POSTERIOR  TRIANGLE  •     143 

temporal  bone  and  the  superior  nuchal  line  to  the  external  occipital  pro- 
tuberance. (2)  From  the  sternal  to  the  acromial  end  of  the  clavicle, 
following  the  line  of  that  bone.  (3)  Join  the  anterior  extremities  of  i  and 
2  by  a  vertical  incision  passing  along  the  back  of  the  external  acustic  meatus 
and  then  down  the  middle  of  the  sterno-mastoid  muscle.  Reflect  the  flap, 
thus  marked  out,  from  before  backwards,  and  note  that  the  skin  is  thicker 
over  the  upper  and  posterior  part  of  the  triangle  than  over  the  lower  and 
anterior  part. 

When  the  skin  is  reflected  the  superficial  fascia  and  the  lower  part  of 
the  platysma  muscle  will  be  exposed. 

The  superficial  fascia  in  the  region  of  the  posterior  triangle 
is  comparatively  thin,  and  embedded  in  its  lower  and  anterior 
part  is  the  lower  and  posterior  part  of  the  platysma. 

The  Platysma. — The  platysma  is  a  thin  sheet  of  muscle 
which  commences  in  the  superficial  fascia  of  the  infra-clavi- 
cular region,  whence  it  ascends  across  the  clavicle  and  through 
the  superficial  fascia  of  the  side  of  the  neck,  to  the  face  where 
its  upper  border  has  been  examined  already  (p.  126).  It 
covers  the  lower  and  anterior  part  of  the  posterior  triangle, 
and  the  upper  and  posterior  part  of  the  anterior  triangle  ;  and 
it  is  supplied  by  the  cervical  branch  of  the  facial  nerve, 
which  emerges  from  the  lower  end  of  the  parotid  gland. 

Dissection. — Make  an  incision  through  the  lower  part  of  the  platysma 
along  the  line  of  the  clavicle,  and  turn  the  part  above  the  incision  upwards 
and  anteriorly.  Whilst  making  the  incision  and  whilst  reflecting  the  muscle, 
be  careful  not  to  injure  the  supraclavicular  cutaneous  nerves  and  the 
external  jugular  vein,  which  lie  directly  subjacent  to  it. 

After  the  platysma  is  reflected,  clean  the  external  jugular  vein,  which 
emerges  from  the  lower  end  of  the  parotid  and  passes  downwards,  in- 
clining posteriorly,  to  the  lower  and  anterior  angle  of  the  posterior  tri- 
angle, where  it  pierces  the  deep  fascia.  Whilst  cleaning  the  vein,  avoid 
injury  to  the  nervus  cutaneus  colli,  which  sometimes  crosses  superficial 
to  the  vein  about  the  middle  of  its  length.  Secure  and  clean  the  posterior 
auricular  vein,  which  descends  behind  the  auricle  and  joins  the  external 
jugular  a  little  below  the  level  of  the  angle  of  the  mandible.  Next,  find 
and  clean  the  superficial  branches  of  the  cervical  plexus  as  they  pierce  the 
deep  fascia.  They  are  (i)  descending  branches,  the  anterior,  middle,  and 
posterior  supra-clavicular  nerves.  (2)  A  transverse  branch,  the  nervus 
cutaneus  colli  (O.T.  transverse  cervical).  (3)  Ascending  branches,  the 
great  auricular  and  the  small  occipital. 

The  anterior  and  middle  sjipra-clavicular  nerves  will  be  found  piercing 
the  deep  fascia  immediately  above  the  clavicle,  the  anterior  at  the  posterior 
border  of  the  sterno-mastoid  and  the  middle  above  the  convexity  of  the 
clavicle.  They  descend  into  the  pectoral  region  as  far  as  the  lower  border 
of  the  second  rib  and  their  lower  portions  will  be  displayed  by  the  dissector 
of  the  arm.  The  posterior  supra-clavicidar  nerves  pierce  the  deep  fascia  at 
a  somewhat  higher  level.  They  descend  across  the  lower  and  anterior  part 
of  the  trapezius  to  the  acromial  region,  and  to  the  skin  of  the  arm  over  the 
upper  part  of  the  deltoid,  where  they  will  be  exposed  by  the  dissector  of 
the  arm. 


144 


HEAD  AND  NECK 


The  Deep  Fascia. — The  deep  fascia  forms  the  superficial 
boundary  or  roof  of  the  posterior  triangle.  It  is  attached 
below  to  the  upper  border  of  the  middle  third  of  the  clavicle  ; 


Great  occipital 

nerve  ._1 
Posterior  'i^^V.. 
auricular  vein   "' 


Small  occipital  nerve 

Great  auricular  nerve   1^.- 
Splenius  capitis 
Accessory  ner\'e 

Levator  scapulae 

Middle  supra- 
clavicular nerve  . 
Posterior  supra-  f  M\ 

clavicular  nerve  " " 

Scalenus  medius 


;='         Nervus  cutan- 

eus  colli 

upper  branch 
Nervus  cutaneus 
colli 


Anterior  supra- 
--    clavicular  nerve. 


Fig.  66. — The  superficial  branches  of  the  cervical  plexus. 

above,  to  the  superior  nuchal  line  of  the  occipital  bone; 
anteriorly  it  is  continuous  with  the  fascia  of  the  stern o-mastoid 
and  posteriorly  with  the  fascia  of  the  trapezius.  It  is  pierced 
by  (i)  the  supra-clavicular  branches  of  the  cervical  plexus,  (2) 
the  external  jugular  vein,  (3)  small  cutaneous  branches  of  the 


POSTERIOR  TRIANGLE  145 

transverse  cervical,  transverse  scapular  (O.T.  suprascapular), 
and  occipital  arteries,  and,  occasionally,  by  the  occipital  artery 
itself.  It  is  not  a  very  strong  layer,  and  it  is  frequently  difficult 
to  display  it  as  a  continuous  sheet.  Over  the  upper  part  of  the 
triangle  it  forms  a  single  layer,  but  below,  it  splits  into  two 
lamellae,  a  superficial  and  a  deep.  The  superficial  layer  which 
is  already  displayed,  is  attached  to  the  upper  border  of  the 
clavicle  from  the  sterno-mastoid  anteriorly  to  the  trapezius 
posteriorly.  It  is  pierced  by  the  external  jugular  vein  and 
the  supraclavicular  nerves. 

Dissection. — Trace  the  supraclavicular  nerves  upwards  through  the  deep 
fascia  to  the  posterior  border  of  the  sterno-mastoid  ;  then,  pulHng  them  aside, 
cut  through  the  superficial  layer  of  the  deep  fascia  immediately  above  the 
clavicle  and  along  the  posterior  border  of  the  sterno-mastoid,  and  turn  it 
upwards.  Introduce  the  handle  of  the  scalpel  behind  the  clavicle  and  note 
that  it  can  be  passed  downwards  as  far  as  the  posterior  border  of  the  lower 
surface  of  the  bone.  Its  further  progress  is  barred  by  the  attachment  of 
the  second  layer  of  the  deep  fascia  to  this  border,  where  it  blends  with  the 
posterior  lamella  of  the  costo-coracoid  membrane.  Pass  the  handle  of  the 
knife  forwards  behind  the  sterno-mastoid  and  note  that,  without  using  any 
great  force,  it  can  be  pushed  medially  until  it  crosses  the  median  plane  ; 
therefore,  the  space  betw^een  the  two  layers  of  deep  fascia  in  the  lower  part 
of  the  posterior  triangle  is  continuous  anteriorly  with  the  space  which  lies 
above  and  posterior  to  the  manubrium  sterni,  between  the  first  and  the  second 
layers  of  the  deep  fascia  of  the  anterior  part  of  the  neck.  Laterally,  this 
space  extends  as  far  as  the  coracoid  process,  and  upwards  to  a  short  distance 
above  the  posterior  belly  of  the  omo-hyoid  muscle.  Clear  away  the  areolar 
tissue  which  lies  between  the  two  layers  of  the  deep  fascia,  and  expose  a 
further  part  of  the  external  jugular  vein,  and  the  terminal  parts  of  the 
transverse  cervical  and  the  transverse  scapular  (suprascapular)  veins,  as 
they  join  the  posterior  border  of  the  external  jugular.  Pull  the  lower  part 
of  the  external  jugular  vein  posteriorly  and  expose  the  termination  of  the 
anterior  jugular  vein  in  its  anterior  border.  Dissect  carefully  behind  the 
clavicle  and  find  the  transverse  scapular  (suprascapular)  artery.  Trace  the 
second  layer  of  the  deep  fascia  upwards  and  note  that  it  is  continuous  with 
the  fascia  which  surrounds  the  posterior  belly  of  the  omo-hyoid  muscle  ; 
indeed  it  is  the  tension  of  this  portion  of  the  deep  fascia  which  holds  the 
posterior  belly  of  the  muscle  down  in  its  position. 

Remove  the  remaining  parts  of  the  deep  fascia,  first  from  the  upper, 
and  then  from  the  lower  part  of  the  triangle,  and  expose  the  floor  and  the 
remaining  contents  of  the  triangle. 

Commence  above,  in  the  region  of  the  junction  of  the  upper  third  and 
the  lower  two-thirds  of  the  posterior  border  of  the  sterno-mastoid,  and 
secure  the  great  auricular,  the  small  occipital,  the  accessory  nerve,  and  the 
nervus  cutaneus  colli.  The  great  auricular  is  most  easily  found.  It  turns 
round  the  posterior  border  of  the  sterno-mastoid,  in  the  region  indicated, 
and  runs  upwards  and  anteriorly,  parallel  with  and  slightly  above  and 
posterior  to  the  external  jugular  vein.  The  small  occipital  will  be  found 
hooking  round  the  lower  border  of  the  accessory  nerve  a  little  above  the 
great  auricular  ;  and  the  nervus  cutaneus  colli  lies  a  little  below  the  great 
auricular. 

Follow    the   small   occipital   and    the   great   auricular   nerves   to   their 

VOL.   II — 10 


146  HEAD  AND  NECK 

terminations,  but  the  nervus  cutaneus  colli  must  be  traced  only  to  the 
point  where  it  crosses  either  superficial  or  deep  to  the  external  jugular  vein. 
It  eventually  divides  into  upper  and  lower  terminal  branches,  which  will  be 
seen  when  the  anterior  triangle  is  dissected. 

Nervus  Occipitalis  Minor. — The  small  occipital  is  a  sensory 
branch  of  the  second  cervical  nerve.  It  emerges  from  under 
cover  of  the  sterno-mastoid,  and  ascends  for  a  short  distance 
along  its  posterior  border,  then  it  passes  to  the  superficial 
surface  of  the  muscle,  pierces  the  deep  fascia,  and  divides 
into  occipital,  mastoid,  and  auricular  branches.  The  occi- 
pital and  mastoid  branches  supply  the  skin  in  the  regions 
indicated  by  their  names.  The  auricular  is  distributed  to  the 
skin  of  the  upper  third  of  the  cranial  surface  of  the  auricle. 

Nervus  Auricularis  Magnus. — This  consists  of  cutaneous 
filaments  derived  from  the  second  and  third  cervical  nerves. 
After  turning  round  the  posterior  border  of  the  sterno-mastoid 
it  runs  upwards  and  anteriorly,  towards  the  angle  of  the 
mandible,  in  the  deep  fascia  on  the  superficial  surface  of 
the  sterno-mastoid,  and  breaks  up  into  three  sets  of  terminal 
branches,  mastoid,  auricular,  and  facial.  The  mastoid  branches 
go  to  the  skin  of  the  mastoid  region.  The  auricular  branches 
supply  the  skin  of  the  lower  two-thirds  of  the  cranial  surface 
and  the  lower  third  of  the  lateral  surface  of  the  auricle.  The 
facial  branches^  which  have  already  been  seen,  ramify  in  the 
posterior  part  of  the  face,  in  the  parotid  and  masseteric  regions. 
Some  of  the  filaments  enter  the  substance  of  the  parotid. 

Dissection. — The  accessory  nerve,  previously  found  at  the  junction  of 
the  upper  third  with  the  lower  two-thirds  of  the  posterior  border  of  the 
sterno-mastoid,  must  now  be  traced  downwards  and  posteriorly,  through 
the  triangle,  to  the  point  where  it  disappears  under  cover  of  the  trapezius, 
at  the  junction  of  the  upper  two-thirds  with  the  lower  third  of  the  anterior 
border  of  that  muscle.  As  the  nerve  is  cleaned,  attempt  to  secure  twigs 
from  the  third  and  fourth  cervical  nerves  which  communicate  with  it  in 
the  posterior  triangle. 

Turn  next  to  the  posterior  belly  of  the  omo-hyoid  muscle,  which 
crosses  the  lower  part  of  the  triangle.  Note  that  it  divides  the  triangle 
into  a  large  upper  or  occipital  portion,  and  a  small  lower  or  subclavian 
portion.  Cut  through  the  fascia  on  the  surface  of  the  muscle,  parallel  with 
the  muscle  fibres,  and  turn  it  upwards  and  downwards  ;  then  turn  the 
upper  border  of  the  muscle  laterally  and  find  the  nerve  from  the  ansa 
hypoglossi,  which  emerges  from  under  cover  of  the  sterno-mastoid  and 
enters  the  deep  surface  of  the  omo-hyoid  to  supply  it. 

Take  away  the  remains  of  the  superficial  layer  of  deep  fascia,  and  the 
areolar  tissue  beneath  it  from  the  upper  part  of  the  triangle.  Whilst 
removing  the  latter  note  a  number  of  lymph  glands  which  lie  embedded 
in  it  along  the  posterior  border  of  the  sterno-mastoid,  superficial  to  the 
stems  and  branches  of  the  cervical  nerves.  At  the  apex  of  the  triangle 
look  for  the  occipital  artery,  which  either  emerges  between  the  adjacent 


POSTERIOR  TRIANGLE  147 

borders  of  the  trapezius  and  the  sterno-mastoid,  or  pierces  the  trapezius  a 
little  further  posteriorly. 

Between  the  accessory  nerve  above  and  the  posterior  belly  of  the  omo- 
hyoid below  find  (i)  the  upper -part  of  the  brachial  plexus  ;  (2)  its  branch 
to  the  subclavius  ;  (3)  its  suprascapular  branch  ;  (4)  its  dorsalis  scapulae 
branch;  (5)  its  long  thoracic  branch;  (6)  branches  from  the  third  and 
fourth  cervical  nerves  to  the  levator  scapulos  ;  (7)  branches  from  the  third 
and  fourth  cervical  nerves  to  the  trapezius,  and  others  which  communicate 
with  the  accessoiy  nerve  in  the  posterior  triangle  ;  and  (8)  the  upper  and 
posterior  part  of  the  transverse  cervical  artery.  Find  the  transverse  cervical 
artery  as  it  appears  from  under  cover  of  the  upper  border  of  the  omo-hyoid. 
It  runs  upwards  and  posteriorly.  Next  secure  the  nerve  to  the  subclavius, 
which  lies  under  cover  of  the  deep  fascia  above  the  omo-hyoid  and  a  short 
distance  behind  the  sterno-mastoid.  Trace  it  upwards  to  its  origin  from 
the  trunk  formed  by  the  union  of  the  fifth  and  sixth  cervical  nerves.  Clean 
the  latter  nerves  and  the  upper  part  of  the  seventh  cervical  nerve,  which 
lies  immediately  below  them.  Then  find  the  suprascapular  nerve,  which 
springs  from  the  lateral  border  of  the  trunk  formed  by  the  fifth  and  sixth 
nerves.  It  lies  immediately  above  the  anterior  part  of  the  posterior  belly 
of  the  omo-hyoid,  and  disappears  under  cover  of  the  posterior  part. 
Turn  the  trunk  formed  by  the  fifth  and  sixth  cervical  nerves  anteriorly  and 
find,  posterior  to  it,  the  upper  roots  of  the  long  thoracic  nerve,  which  spring 
from  the  fifth  and  sixth  nerves,  and  are  emerging  through  the  fibres  of  the 
scalenus  medius  muscle.  The  nervus  dorsalis  scapulae  (O.T.  nerve  to  the 
rhomboids)  lies  at  a  slightly  higher  level  than  the  suprascapular  nerve.  It 
springs  from  the  fifth  cervical  nerve,  runs  downwards  and  posteriorly,  and 
disappears,  through  the  floor  of  the  triangle,  between  the  adjacent  borders 
of  the  levator  scapulae  above  and  the  scalenus  medius  below.  Above  the 
dorsal  scapular  nerve  are  the  branches  from  the  third  and  fourth  cervical 
nerves  to  the  trapezius  and  the  communications  to  the  accessory  nerve. 

When  the  structures  mentioned  above  have  been  found  and  cleaned, 
proceed  to  the  dissection  of  the  subclavian  portion  of  the  triangle.  Find 
the  transverse  scapular  artery  (O.T.  suprascapular),  which  lies  behind  the 
clavicle,  and  therefore,  strictly  speaking,  outside  the  limits  of  the  triangle. 
Then  remove  the  second  layer  of  deep  cervical  fascia  which  binds  the 
posterior  belly  of  the  omo-hyoid  to  the  posterior  border  of  the  clavicle,  and 
find  behind  it  (i)  a  further  part  of  the  external  jugular  vein  ;  (2)  a  further 
part  of  the  transverse  cervical  artery  ;  (3)  the  lower  part  of  the  nerve  to  the 
subclavius  ;  (4)  the  upper  portion  of  the  third  part  of  the  subclavian  artery  ; 

(5)  the  lowest  root  and  the  lower  parts  of  the  trunks  of  the  brachial  plexus  ; 

(6)  a  part  of  the  long  thoracic  nerve  ;  (7)  supraclavicular  lymph  glands. 
First  clean  the  lower  end  of  the  external  jugular  vein  and  follow  it 

behind  the  clavicle  to  its  termination  in  the  subclavian  vein.  Note  the 
valves  near  its  lower  end.  Next  clean  the  transverse  cervical  artery  and 
the  nerve  to  the  subclavius.  Follow  the  nerve  to  the  subclavius  across 
the  front  of  the  third  part  of  the  subclavian  artery  ;  and  afterwards  clean 
the  lower  part  of  the  subclavian  artery  and  the  adjacent  part  of  the 
brachial  plexus,  which  lies  behind  and  above  the  artery.  Note  that  the 
artery  and  the  plexus  are  covered  by  a  layer  of  deep  cervical  fascia,  the 
backward  prolongation  of  the  prevertebral  layer  of  fascia,  which  passes  on 
to  them  from  the  lateral  border  of  the  scalenus  anterior,  and  is  prolonged 
along  them  to  become  continuous  with  the  sheath  of  the  axillary  artery. 

As  the  areolar  tissue   is  cleared  from  the  subclavian   portion  of  the 
triangle  a  number  of  supraclavicular  lymph  glands  may  be  noted.     They 
receive  lymph  from  the  axillary  glands,  and  they  transmit  it  to  the  large 
lymph  vessels  at  the  root  of  the  neck. 
II— 10  a 


14S 


HEAD  AND  NECK 


After  the  contents  of  the  lower  part  of  the  triangle  are  thoroughly  cleaned, 
remove  the  remains  of  the  fascia  covering  the  muscles  which  form 
the  floor  of  the  triangle.  Note  that  this  fascia  is  continuous  anteriorly, 
round  the  tips  of  the  transverse  processes  of  the  cervical  vertebrse  with  the 
prevertebral  fascia.     Posteriorly  it  blends  with  the  sheaths  of  the  deeper 


"--Digastric 
Nerve  to  thyreo-hyoid 
Thyreo-hyoid 
Superior  thyreoid  artery 
Omo-hyoid 


Transverse 
=  capular  artery 
Scalenus  anterior 
Subclavian  artery 

Subclavian  vein 


Suprascapular 

N 


Fig.  67. — The  Triangles  of  the  Neck  seen  from  the  side.  The  clavicular  head 
of  the  sterno-mastoid  muscle  was  small,  and  therefore  a  considerable  part 
of  the  scalenus  anterior  muscle  is  seen. 


muscles  at  the  back  of  the  neck  ;  above  it  is  attached  to  the  superior 
nvichal  line  ;  and  below,  as  already  stated,  it  is  prolonged  into  the  axilla 
along  the  axillary  vessel?  and  nerves. 

Boundaries  and  Contents  of  the  Posterior  Triangle. — The 

dissection  of  the  triangle  should  be  completed  in  two  days. 
On  the  third  day  the  dissector  should  revise  his  knowledge 
of  the  boundaries  and  the  relative  positions  of  the  contents. 


POSTERIOR  TRIANGLE  149 

The  triangle  is  bounded  anteriorly  by  the  posterior  border 
of  the  sterno-mastoid  ;  posteriorly  by  the  anterior  border  of  the 
trapezius ;  below  by  the  upper  border  of  the  middle  third 
of  the  clavicle ;  and  above  by  the  superior  nuchal  line  of  the 
occipital  bone,  or  by  the  meeting  of  the  upper  ends  of  the  sterno- 
mastoid  and  the  trapezius.  The  roof  is  formed  by  the  deep 
cervical  fascia,  which  is  covered  by  superficial  fascia  and  skin, 
and  in  its  lower  and  anterior  part  by  the  platysma,  which  is 
embedded  in  the  superficial  fascia.  It  is  pierced  by  (i)  the 
external  jugular  vein  at  the  lower  and  anterior  angle;  (2)  the 
supraclavicular  nerves,  a  short  distance  above  the  clavicle  ; 
(3)  small  cutaneous  branches  of  the  transverse  scapular,  trans- 
verse cervical,  and  occipital  arteries;  (4)  lymphatic  vessels 
passing  from  the  superficial  structures  to  the  glands  in  the 
triangle.  It  is  frequently  stated  that  the  small  occipital,  the 
great  auricular,  and  the  cervical  cutaneous  nerves  also 
pierce  the  roof.  As  a  general  rule  they  turn  round  the 
posterior  border  of  the  sterno-mastoid  under  cover  of  the 
fascia,  and  pierce  the  fascia  as  it  lies  on  the  muscle. 

The  floor  is  formed  by  the  splenius  capitis,  the  levator 
scapulae,  the  scalenus  medius,  and  the  scalenus  posterior 
muscles,  with  the  addition,  occasionally,  of  a  small  part  of  the 
semispinalis  capitis  (O.T.  complexus)  above,  and  the  upper 
serration  of  the  serratus  anterior  below ;  the  latter  appears 
in  the  area  of  the  triangle  only  when  the  clavicle  is  very 
fully  depressed.  The  muscles  of  the  floor  are  covered  with 
a  layer  of  fascia  which  is  the  backward  continuation  of  the 
prevertebral  fascia  of  the  anterior  cervical  region. 

The  contents  of  the  posterior  triangle  are  : — 

1.  Fatty  areolar  tissue. 

2.  The  posterior  belly  of  the  omo-hyoid  muscle. 

3.  Lymph        f  Post  sterno-mastoid. 

Glands,   ( Supraclavicular. 

'  Third  part  of  subclavian. 


{Third  part  or  subclavian. 
Transverse  cervical  and  its  terminal  branches. 
Occipital  (sometimes). 
/"External  jugular. 
I  Transverse  cervical. 
5.   Veins, '-^       "1  Transverse  scapular  (O.T.  suprascapular). 
[Termination  of  anterior  jugular. 

■••  The  transverse  scapular  artery  (O.T.  suprascapular)  lies  posterior  to 
the  clavicle  and  is  not,  strictly  speaking,  in  the  triangle. 

^  The  subclavian  vein  is  posterior  to  the  clavicle  and  therefore  is  not 
contained  within  the  triangle. 
II— 10& 


ISO 


HEAD  AND  NECK 


> Branches  of  cervical  plexus. 


6.  Nerves, 


'Accessory. 
Small  occipital. 
Great  auricular. 
Nervus  cutaneus  colli. 
To  levator  scapulae. 
,,  trapezius. 
,,  scalenus  medius. 
*    ,,         ,,       posterior. 
Supraclavicular. 

To  posterior  belly  of  omo-hyoid  from  ansa  hypoglossi. 
Trunks  of  brachial  plexus. 
The  nervus  dorsalis  scapulae.  ] 
,,    long  thoracic.  |_  Branches   of  the   brachial 

,,    suprascapular.  j 

,,    nerve  to  the  subclavius.  j 


plexus. 


Some  of  the  contents  of  the  triangle  which  are  now 
displayed  require  further  consideration. 

The  Posterior  Belly  of  the  Omo-hyoid  Muscle. — The 
posterior  belly  of  the  omo-hyoid  muscle  springs  from  the 
upper  border  of  the  scapula  and  upper  transverse  scapular 
ligament.  It  enters  the  posterior  triangle,  at  its  lower  and 
posterior  angle,  and  runs  upwards  and  anteriorly,  at  a 
variable  distance  from  the  clavicle,  to  the  posterior  border 
of  the  sterno- mastoid.  Either  immediately  behind  or 
under  cover  of  the  posterior  border  of  the  sterno-mastoid  it 
joins  the  intermediate  tendon  which  connects  it  with  the 
anterior  belly.  Its  nerve  has  already  been  seen  entering 
its  deep  surface  (p.  146)  it  divides  the  posterior  triangle 
into  a  lower  or  subclavian  portion  and  an  upper  or  occipital 
portion. 

The  Accessory  Nerve  (O.T.  Spinal  Accessory).  —  The 
portion  of  the  accessory  nerve  which  appears  in  the  posterior 
triangle  consists  of  fibres  which  arise  from  the  cervical  part 
of  the  spinal  medulla  and  with  them  are  incorporated  some 
filaments  derived  from  the  second  cervical  nerve.  Before 
appearing  in  their  present  situation  the  spinal  fibres  entered 
the  cranium  through  the  foramen  magnum  and  left  it  by  pass- 
ing through  the  jugular  foramen  ;  then  they  passed  downwards 
and  posteriorly,  through  the  deeper  fibres  of  sterno-mastoid, 
where  they  received  the  communication  from  the  second  cervical 
nerve.  As  already  pointed  out,  the  nerve  usually  enters  the 
posterior  triangle  at  the  level  of  the  union  of  the  upper  third 
with  the  lower  two-thirds  of  the  posterior  border  of  the  sterno- 
mastoid.  It  runs  downwards  and  posteriorly  through  the 
triangle,  along  the  line  of  the  levator  scapulae,  and  disappears 


POSTERIOR  TRIANGLE  151 

under  the  trapezius  at  the  junction  of  the  upper  two-thirds 
with  the  lower  third  of  its  anterior  border.  As  it  enters  the 
triangle  the  small  occipital  nerve  turns  round  its  lower  border, 
and,  as  it  crosses  the  triangle,  it  is  joined  by  twigs  from  the 
third  and  fourth  cervical  nerves. 

The  Branches  of  the  Cervical  Plexus. — The  dissector 
should  note  that  whilst  many  of  the  branches  of  the  cervical 
plexus  lie  within  the  area  of  the  posterior  triangle,  the 
plexus  itself  is  under  cover  of  the  upper  part  of  the  sterno- 
mastoid,  where  it  will  be  exposed  and  studied  when  the 
sterno  -  mastoid  is  reflected.  The  branches  which  appear 
in  the  triangle  are  the  superficial  bra?iches — the  small  occipital, 
the  great  auricular,  the  nervus  cutaneus  colli,  and  the  supra- 
clavicular nerves ;  and  the  deep  posterior  branches^  that  is, 
the  nerves  to  the  scalenus  medius  and  posterior,  the  nerve 
to  the  levator  scapulae,  the  branches  to  the  trapezius  and  the 
communication  to  the  accessory  nerve. 

The  Third  Part  of  the  Subclavian  Artery.  —  Only  a 
portion  of  this  part  of  the  subclavian  artery  is  in  the  triangle ; 
the  lower  and  lateral  part  is  behind  the  clavicle.  The  part 
in  the  triangle  is  situated  deeply  in  the  anterior  inferior 
angle  and  below  the  omo-hyoid  muscle.  It  is  covered  zvith  the 
skin,  superficial  fascia,  the  platysma,  deep  fascia,  the  external 
jugular  vein,  the  ends  of  the  transverse  scapular,  and  trans- 
verse cervical  veins,  and  the  nerve  to  the  subclavius  muscle. 
Behind  it  is  the  lowest  trunk  of  the  brachial  plexus,  which 
separates  it  from  the  insertion  of  the  scalenus  medius.  Below, 
it  rests  upon  the  first  rib,  against  which  it  can  be  compressed, 
and,  more  medially,  on  the  cervical  pleura. 

The  Brachial  Plexus  and  its  Supraclavicular  Branches. — 
Only  the  upper  portion  of  the  brachial  plexus  lies  in  the 
region  of  the  posterior  triangle,  i.e.  the  roots,  the  trunks,  and 
some  of  the  branches ;  the  remainder  lies  either  posterior  to 
the  clavicle  or  in  the  axilla.  The  cervical  portion  lies  in  the 
lower  and  anterior  part  of  the  posterior  triangle  partly  in 
the  occipital  and  partly  in  the  supraclavicular  areas.  The 
detailed  study  of  the  plexus  should  be  left  till  the  fifth  day 
after  the  body  has  been  placed  upon  its  back,  when  the 
dissector  of  the  head  and  neck  will  assist  the  dissector  of  the 
upper  extremity  to  disarticulate  the  clavicle  and  to  lay  bare 
the  whole  of  the  plexus  (p.  160). 

The  fourth  day  after  the  body  has  been  placed  upon  its 


152 


HEAD  AND  NECK 


back  should  be  devoted  to  the  study  of  the  temporal  region 
and  the  anterior  part  of  the  scalp. 


THE  SCALP  AND  THE  SUPERFICIAL  STRUCTURES 
OF  THE  TEMPORAL  REGION. 

Under  the  term  "  scalp  "  are  included  the  soft  structures 
which  cover  the  vault  of  the  cranium  above  the  temporal 
ridges  and  anterior  to  the  superior  nuchal  line.  Its  con- 
stituent parts  are  arranged  in  five  layers  :  (i)  skin;  (2)  super- 
ficial fascia  ;   (3)  the  epicranius,  consisting  of  four  muscular 


L-  Integument 


C,«JJ 


Dura  mater 


Fig.  68. — Section  through  the  Scalp  and  Cranial  Wall. 

bellies,  the  two  occipitales  and  the  two  frontales  muscles,  and 
the  aponeurosis  called  the  galea  aponeurotica,  which  connects 
them  together;  (4)  a  layer  of  loose  areolar  tissue ;  (5)  the 
periosteum,  which  is  here  called  the  pericranium.  In  the 
temporal  region  the  wall  of  the*  cranium  is  much  more  thickly 
covered  than  in  the  scalp  area,  and  it  is  possible  to  distinguish 
eight  layers  of  soft  tissues  between  the  surface  and  the  bone : 
(i)  skin;  (2)  superficial  fascia  ;  (3)  extrinsic  muscles  of  the 
ear ;  (4)  the  thin  lateral  extensions  of  the  galea  aponeurotica ; 
(5)  a  thin  layer  of  fascia  descending  from  the  temporal  ridge 
to  the  auricle  ;  (6)  the  strong  temporal  fascia  ;  (7)  the  temporal 
muscle ;  (8)  periosteum. 

TAe  Scalp. — The  scalp  and  the  superficial  temporal  region 
are  richly  supplied  with  blood  vessels  and  nerves,  which  all 


AURICLE  153 

enter  from  the  periphery,  passing  into  the  superficial  fascia 
after  piercing  the  deep  fascia  of  adjacent  regions.  As  a 
consequence  of  this  arrangement  large  flaps  of  the  scalp  may 
be  torn  from  the  centre  towards  the  margin,  but,  so  long  as 
they  remain  attached  at  the  periphery,  their  sources  of 
vitality  are  not  seriously  interfered  with,  and  if  they  are  cleaned 
and  replaced  healing  occurs  rapidly  and  satisfactorily. 

Dissection. — The  skin  has  already  been  removed  from  the  anterior 
parts  of  the  scalp  and  the  temporal  region.  A  median  longitudinal  in- 
cision must  now  be  made  through  the  skin  of  the  posterior  part  of  the 
scalp  as  far  as  the  external  occipital  protuberance,  and  the  flap  on  either 
side  of  the  incision  must  be  turned  downwards  and  posteriorly  to  the 
superior  nuchal  line.  When  this  has  been  done  the  dissector  should  ex- 
amine the  auricle  of  the  external  ear,  and  familiarise  himself  with  its  various 
parts  before  he  commences  the  dissection  of  its  extrinsic  muscles. 


Crus  antihelicis 


Fossa  triangularis 


Tragus 
Incisura 
\       intertragica 


^l 


Lobulus  -\ w 

Fig.  69.  —  The  Auricle. 

Auricle  or  Pinna. — The  auricle  consists  of  a  thin  plate  of 
yellow  fibro-cartilage,  covered  with  integument.  It  is  fixed  in 
position  by  certain  ligaments,  and  possesses  two  sets  of  feeble 
muscles — viz.,  one  group  termed  the  extrinsic  muscles.,  passing 
to  the  cartilage  from  the  aponeurosis  of  the  epicranius  and 
the  mastoid  process,  and  a  second  group  in  connection  with 
the  cartilage  alone,  and  therefore  called  the  iiitrinsic  muscles. 

The  concha  is  the  wide  and  deep  fossa  which  leads  into 
the  external  meatus ;  the  antiJielix  is  the  curved  prominence 
w^hich  bounds  this  posteriorly ;  the  helix  is  the  folded  or  in- 
curved margin  of  the  auricle ;  and  the  lobule  is  its  soft 
dependent  part.  The  concha  is  partially  subdivided  into  an 
upper  and  a  lower  part  by  the  commencement  of  the  helix, 
which  curves  upwards  and  forwards  on  its  floor  to  become 
continuous  with  the  anterior  border  of  the  auricle.  This 
portion  of  the  helix  is  called  the  crus  helicis.     A  small  pro- 


Intrinsic  muscles,  - 


154  HEAD  AND  NECK 

minence  anterior  to  the  meatus,  and  projecting  posteriorly  so 
as  to  overshadow  it,  is  termed  the  tragus^  whilst  a  similar 
eminence  posterior  to  and  below  the  meatus  receives  the  name 
of  the  antitragus.  The  notch  between  these  two  prominences 
is  termed  the  incisura  intertragica.  But  it  will  be  noted  that 
the  upper  end  of  the  antihelix  bifurcates,  and  in  this  way  two 
fossae  are  marked  off  from  each  other;  one — the  fossa  of  the 
helix,  or  scaphoid  fossa — is  placed  between  the  helix  and  the 
antihelix,  and  the  other — the  fossa  of  the  antihelix,  or  triangular 
fossa  —  is  situated  between  the  two  diverging  crura  of  the 
antihelix. 

[Anterior. 
Ligaments,     .         .         .         .     \  Superior. 

(^  Posterior. 

{Auricularis  anterior. 
Auricularis  superior. 
Auricularis  posterior. 

'Musculus  helicis  major.   "^ 

Musculus  helicis  minor.    I  Upon  the  lateral  face  of  the 

Musculus  tragicus.  j      cartilage. 

Musculus  antitragicus.      J 

Musculus  transversus.       )  Upon    the    cranial   face   of 
, Musculus  obliquus.  /     the  cartilage. 

Dissection. — When  the  dissector  has  noted  the  various  parts  of  the 
auricle  he  should  endeavour  to  display  its  extrinsic  muscles  ;  they  are  the 
auriculares  anterioi'  [O.T.  attrahens),  stiperior  {O.T.  attollens),  dcnd  posterior 
(O.T.  retrahens).  The  two  former  spring  from  a  lateral  prolongation 
of  the  galea  aponeurotica  into  the  temporal  region.  The  anterior  is 
inserted  into  the  front  of  the  helix,  and  the  superior  into  the  cranial  surface 
of  the  auricle.  To  display  them  pull  the  auricle  downwards  and  posteriorly, 
and  carefully  remove  the  superficial  fascia  and,  at  the  same  time,  avoid  injury 
to  the  auriculo-temporal  nerve,  the  temporal  branches  of  the  facial  nerve, 
and  the  branches  of  the  superficial  temporal  artery  which  are  ascending 
through  the  superficial  fascia  of  the  temporal  region  to  the  scalp.  The 
auricularis  posterior  arises  from  the  outer  surface  of  the  mastoid  part  of 
the  temporal  bone  and  passes  anteriorly  to  its  insertion  into  the  cranial 
aspect  of  the  concha.  To  display  it  pull  the  auricle  anteriorly  and  remove 
the  fascia  from  the  surface  of  the  muscle,  at  the  same  time  secure  the 
posterior  auricular  artery  and  nerve  as  these  ascend  posterior  to  the  external 
meatus.  As  this  is  being  done  one  or  more  mastoid  lymph  glands  may 
be  seen,  and  care  must  be  taken  to  avoid  injuring  the  branch  of  the 
posterior  auricular  nerve  to  the  occipitalis  muscle,  which  passes  posteriorly 
along  the  lower  border  of  the  auricularis  posterior  or  on  its  deep  surface. 

The  auriculares  muscles  are  supplied  by  the  facial  nerve ;  the  anterior 
and  the  anterior  part  of  the  superior  by  its  temporal  branches,  and  the 
posterior  and  the  posterior  part  of  the  superior  by  the  posterior 
auricular  branch.  After  the  auriculares  muscles  have  been  defined  remove 
the  skin  from  the  entire  extent  of  the  auricle  to  display  the  cartilage,  the 
ligaments,  and  the  intrinsic  muscles.^  Great  care  is  required  to  make  a 
successful  dissection. 

^  In  most  cases  it  will  be  advisable  to  defer  this  part  of  the  dissection  till 
the  body  is  turned  on  its  back  for  the  second  time  (p.  200). 


AURICLE  155 

The  auricular  cartilage  extends  throughout  the  entire  auricle,  with  the 
exception  of  the  lobule  and  the  portion  between  the  tragus  and  the  helix. 
These  portions  are  composed  merely  of  integument,  fatty  tissue,  and 
condensed  connective  tissue.  The  shape  of  the  cartilage  corresponds  with 
that  of  the  auricle  itself.  It  shows  the  same  elevations  and  depressions, 
and  by  its  elasticity  it  serves  to  maintain  the  form  of  the  auricle.  But  it 
also  enters  into  the  formation  of  the  cartilaginous  or  lateral  portion  of  the 
external  acustic  meatus.  By  its  medial  margin  this  part  of  the  cartilage 
is  firmly  fixed  by  fibrous  tissue  to  the  rough  outer  edge  of  the  auditory 
process  of  the  temporal  bone,  but  it  does  not  form  a  complete  tube.  It  is 
deficient  above  and  anteriorly,  and  here  the  tube  of  the  meatus  is  completed 
by  tough  fibrous  membrane,  which  stretches  between  the  tragus  and  the 
commencement  of  the  helix. 

In  a  successful  dissection  of  the  cartilage  of  the  auricle,  two  other  points 
will  attract  the  attention  of  the  student.  The  first  is  a  deep  slit,  which 
passes  upwards  so  as  to  separate  the  lower  part  of  the  cartilage  of  the 
helix,  termed  the  p7'ocessus  helicis  caudahis,  from  the  cartilage  of  the  anti- 
tragus  ;  the  second  is  a  sharp  spur  of  cartilage  which  projects  anteriorly 
from  the  helix,  at  the  level  of  the  upper  margin  of  the  zygoma.  This  is 
termed  the  spitta  helicis. 

The  Ligaments  of  the  Auricle. —The  ligaments  are  three  bands  of 
fascia.  The  anterior  passes  from  the  spine  of  the  helix  to  the  root  of  the 
zygoma.  The  superior  and  posterior  are  both  attached  to  the  cartilage  in 
the  region  of  the  concha  ;  the  former  blends  above  with  the  temporal  fascia, 
and  the  latter  is  attached  to  the  mastoid  portion  of  the  temporal  bone. 

The  Intrinsic  Muscles  of  the  Auricle. — The  two  muscles  of  the  helix, 
the  tragicus  and  the  antitragicus,  are  placed  upon  the  lateral  face  of  the 
cartilage.  The  transversus  and  the  obliquus  lie  upon  the  cranial  surface  of 
the  auricle. 

The  musculus  antitragicus  is  the  best-marked  member  of  the  lateral 
group.  It  lies  upon  the  lateral  surface  of  the  antitragus,  and  its  fibres  pass 
obliquely  upwards  and  posteriorly.  Some  fasciculi  can  be  traced  to  the 
processus  helicis  caudatus. 

The  musculus  tragicus  is  a  minute  bundle  of  short  vertical  fibres 
situated  upon  the  lateral  surface  of  the  tragus.  When  well  developed  a 
slender  fasciculus  may  sometimes  be  observed  to  pass  upwards  from  it  to 
the  anterior  part  of  the  helix,  where  it  is  inserted  into  the  spine  of  the  helix. 

The  musculus  helicis  major  is  a  well-marked  band,  which  springs  from 
the  spina  helicis,  and  extends  upwards  upon  the  anterior  part  of  the  helix, 
to  be  inserted  into  the  skin  which  covers  it. 

The  musculus  helicis  minor  is  a  minute  bundle  of  fleshy  fibres  which  is 
placed  upon  the  crus  helicis  as  it  crosses  the  bottom  of  the  concha. 

The  musculus  transversus  auriculce  is  found  upon  the  cranial  aspect  of 
the  auricle.  It  is  generally  the  most  strongly  developed  muscle  of  the 
series,  and  its  fibres  bridge  across  the  hollow  which,  on  this  aspect  of  the 
auricle,  corresponds  to  the  antihelix. 

The  musculus  obliquus  aurictdcB  is  composed  of  some  vertical  fasciculi 
bridging  across  the  depression  which  corresponds  to  the  eminence  of  the 
lower  limb  of  the  antihelix. 

After  the  auricular  muscles  and  the  auricle  have  been  dissected,  trace 
the  temporal  branches  of  the  facial  nerve,  the  branches  of  the  super- 
ficial temporal  vessels,  and  the  auriculo-temporal  nerve  upwards,  from 
the  point  where  they  emerge  from  under  cover  of  the  upper  end  of  the 
parotid  through  the  superficial  fascia  of  the  temporal  region  to  their  termina- 
tions in  the  superficial  fascia  of  the  scalp.  About  half  an  inch  behind  the 
zygomatic  process  of  the  frontal  bone  (O.T.  external  angular  process)  find 


156  HEAD  AND  NECK 

the  zygomatico-temporal  branch  of  the  maxillary  nerve.  Next  pull  the 
auricle  anteriorly  and  trace  the  posterior  auricular  ner\^e  to  its  termination 
in  the  occipitalis  muscle,  and  in  the  intrinsic  and  extrinsic  muscles 
of  the  auricle,  and  the  posterior  auricular  artery  to  its  anastomoses  with 
the  occipital  and  superficial  temporal  arteries.  After  this  part  of  the 
dissection  is  completed,  turn  to  the  anterior  part  of  the  scalp  and  find 
the  medial  and  lateral  branches  of  the  supra-orbital  nerve.  The  medial 
branch  pierces  the  fibres  of  the  frontalis  and  the  lateral  branch  pierces 
the  galea  aponeurotica  a  little  further  posteriorly.  Trace  both  branches 
backwards  through  the  superficial  fascia  as  far  as  possible  ;  they  extend  to 
the  level  of  the  lambdoid  suture.  Then  secure  the  supra-trochlear  nerve, 
which  pierces  the  frontalis  above  the  medial  margin  of  the  orbit,  and  trace 
it  upwards  to  its  termination.  With  the  branches  of  the  supra-orbital  nerve 
are  branches  of  the  supra-orbital  arter}',  and  the  supra-trochlear  nerve  is 
accompanied  by  the  frontal  branch  of  the  ophthalmic  arter}\ 

^Yhen  the  ner\-es  and  vessels  in  the  anterior  region  have  been  cleaned, 
the  head  should  be  turned  well  over  to  the  opposite  side,  and  the  branches 
of  the  occipital  arter\'  and  the  great  occipital  nerve  should  be  sought  for  in 
the  posterior  region  ;  they  radiate  upwards  and  anteriorly  from  the  upper 
extremity-  of  the  trapezius.  After  they  have  been  secured,  the  occipitalis 
muscle  must  be  cleaned.  It  springs  from  the  lateral  part  of  the  sviperior 
nuchal  Hne,  and  after  a  short  course  upwards  and  anteriorly  it  terminates  in 
the  galea  aponeurotica.  The  remains  of  the  superficial  fascia  should  now 
be  removed  from  the  surface  of  the  galea  aponeurotica  (O.T.  epicranial 
aponeurosis),  and  then  the  dissector  should  make  a  survey  of  the  vessels 
and  nerves  which  are  met  with  in  the  scalp  and  the  superficial  fascia  of  the 
temporal  region. 

Nerves  and  Vessels  of  the  Scalp  and  the  Superficial 
Temporal  Eegion. — Branches  of  ten  nerves  are  found,  on  each 
side,  in  the  superficial  fascia  of  the  region  which  lies  above 
the  supra-orbital  margin,  the  zygomatic  arch  and  the  superior 
nuchal  line.  Of  these,  five  lie  mainly  anterior  to  the  auricle 
and  five  posterior  to  it ;  and  of  each  group  four  are  sensory 
and  one  is  motor.  The  four  sensory  nerves  anterior  to  the 
auricle  are  all  branches  of  the  trigeminal  nerve.  They  are 
the  supra-trochlear  and  supra-orbital  branches  of  the  first  or 
ophthalmic  division  :  the  zygomatico-temporal  branch  of  the 
maxillary  or  second  division;  and  the  auriculo -temporal  branch 
of  the  mandibular  or  third  division.  The  motor  nerve  is  the 
temporal  branch  of  the  facial  nen'e. 

The  four  sensory  nerves,  distributed  mainly  to  the  scalp 
area  behind  the  auricle,  are  the  great  auricular  and  the  sjnall 
occipital  branches  of  the  cervical  plexus ;  the  great  occipital^ 
which  is  the  medial  division  of  the  posterior  branch  of  the 
second  cervical  nerv^e ;  and  the  smallest  occipital^  not  yet  seen, 
but  which  will  be  displayed  when  the  body  is  turned  on  its 
face.  It  lies  medial  to  the  great  occipital,  and  is  the  medial 
division  of  the  posterior  branch  of  the  third  cervical  nerve. 


XERVE?  AND  VESSELS   OF   SCALP  157 

The  motor  nen-e  distributed  posterior  to  the  auricle  is  the 
posterior  auricular  branch  of  the  facial  nerve. 

The  arteries  distributed  to  the  scalp  are  five  in  number  on 
each  side;  they  anastomose  freely,  and  are  derived,  either 
indirectly  or  directly,  from  the  internal  and  external  carotid 
arteries.  Three  are  distributed  mainly  anterior  to,  and  two 
posterior  to  the  region  of  the  auricle.  The  three  anterior  to 
the  auricle  are  the  frontal  and  supra-orbital  branches  of  the 
ophthalmic  branch  of  the  internal  carotid,  which  accompany 
the  supra-trochlear  and  supra-orbital  nenxs,  and  the  superficial 
temporal  branch  of  the  external  carorid.  This  branch  divides 
into  two  main  branches,  an  anterior,  which  accompanies  the 
temporal  branches  of  the  facial  nerve,  and  is  usually  a  very 
tortuous  vessel,  and  a  posterior  branch,  which  accompanies  the 
auriculo-temporal  nen^e,  as  it  ascends  anterior  to  the  auricle 
towards  the  vertex  of  the  cranium.  The  two  arteries  posterior 
to  the  auricle  are  both  branches  of  the  external  carotid.  They 
are  the  posterior  auriailar^  which  accompanies  the  posterior 
auricular  branch  of  the  facial  nerve  to  the  mastoid  region 
and  the  posterior  part  of  the  parietal  region,  and  the  occipital, 
which  is  distributed  to  the  occipital  area  and  posterior  part 
of  the  parietal  area. 

The  terminations  of  the  veins  wiiich  drain  the  blood  from 
the  scalp  are  as  follows.  The  frontal  and  supra-orbital  veins 
unite,  at  the  medial  border  of  the  orbit,  to  form  the  angular 
vein,  which  is  the  commencement  of  the  anterior  facial  vein 
already  dissected  (p.  131;.  The  blood  it  conveys  passes 
eventually  to  the  internal  jugular  vein.  The  superficial 
temporal  vein  accompanies  the  corresponding  arter}-.  It  unites, 
immediately  above  the  posterior  root  of  the  zygoma,  with  the 
middle  temporal  vein,  which  pierces  the  temporal  fascia  at 
that  point  The  trunk  formed  by  the  union  of  the  superficial 
and  middle  temporal  veins  is  the  posterior  facial  vein,  which 
descends  through  the  parotid  gland,  emerges  from  under 
cover  of  its  lower  end  and  terminates  immediately  below  the 
angle  of  the  mandible  by  joining  with  the  anterior  facial  vein 
to  form  the  common  facial  vein.  \\Tiilst  in  the  gland,  it  gives 
oflf  the  commencement  of  the  external  jugular  vein.  The 
posterior  auricular  vein  descends  posterior  to  the  external 
meatus  and  terminates  in  the  external  jugular  vein.  The 
occipital  vein  accompanies  the  occipital  artery  into  the  sub- 
occipital region,  and  ends  in  the  sub-occipital  venous  plexus. 


iS8  HEAD  AND  NECK 

In  addition  to  the  arteries  and  veins  there  are  numerous 
lymph  vessels  in  the  scalp,  but  they  cannot  be  displayed  by 
ordinary  dissecting  methods.  Nevertheless,  it  is  important 
that  the  student  should  remember  their  usual  terminations. 
The  lymph  vessels  of  the  anterior  area  end  in  small  lymph 
glands  which  are  embedded  in  the  superficial  surface  of  the 
parotid  gland.  Those  of  the  posterior  area  terminate  either 
in  lymph  glands  which  lie  superficial  to  the  mastoid  part  of 
the  temporal  bone,  or  in  occipital  lymph  glands,  which  lie  in 
the  neighbourhood  of  the  superior  nuchal  line. 

Dissection, — After  the  vessels  and  nerves  of  the  scalp  have  been  traced, 
the  dissector  should  cut  through  the  fibres  of  the  orbicularis  oculi  and  the 
frontalis  over  the  medial  part  of  the  supra-orbital  eminence  and  display  the 
corrugator  supercilii  muscle.  It  springs  from  the  medial  end  of  the 
supra-orbital  ridge  of  the  frontal  bone  and  passes  anteriorly  and  laterally, 
through  the  fibres  of  the  orbicularis  oculi,  to  its  insertion  into  the  skin  of 
the  eyebrow.     It  is  supplied  by  the  temporal  branch  of  the  facial  nerve. 

Galea  Aponeurotica  (O.T.  Epicranial  Aponeurosis). — The 

galea  aponeurotica  is  fully  exposed  as  soon  as  the  superficial 
fascia  of  the  scalp  is  completely  removed.  It  is  a  strong 
layer  of  aponeurosis  connected  anteriorly  with  the  frontal 
bellies  of  the  epicranius,  posteriorly  with  the  occipital  belhes, 
and  between  the  occipital  bellies,  with  the  external  occipital 
protuberance  and  the  medial  parts  of  the  superior  nuchal  lines, 
or  with  the  supreme  nuchal  lines  when  they  are  present. 
Laterally  it  becomes  thinner,  descends  over  the  upper  part  of 
the  temporal  fascia,  and  gives  origin  to  the  anterior  and 
superior  auriculares  muscles.  It  is  so  closely  connected 
with  the  superjacent  skin,  by  the  dense  superficial  fascia, 
that  the  two  cannot  be  separated,  except  with  the  aid  of 
the  cutting  edge  of  the  scalpel ;  but  above  the  supra-orbital 
ridges,  the  temporal  ridges,  and  the  superior  nuchal  lines  it 
is  only  loosely  connected  to  the  pericranium  by  the  layer 
of  loose  areolar  tissue ;  therefore  the  three  closely  connected 
superficial  layers,  the  skin,  superficial  fascia,  and  the  galea 
aponeurotica,  can  easily  be  torn  from  the  pericranium,  a 
circumstance  taken  advantage  of  by  the  Indians  who  scalped 
their  defeated  foes.  The  looseness  of  the  areolar  tissue 
beneath  the  galea  aponeurotica  permits  the  latter  to  be 
drawn  forwards  and  backwards  by  the  alternate  contractions 
of  the  occipitalis  and  frontalis  muscles,  and,  as  it  moves,  it 
carries  with  it  the  skin  and  superficial  fascia  with  which 
it  is  so  closely  blended. 


SCALP  159 

Dissection. — The  dissector,  after  studying  the  attachments  of  the  galea 
aponeurotica,  and  after  he  has  made  himself  thoroughly  conversant  with 
the  nerve  and  vascular  supply  of  the  scalp,  and  has  appreciated  the  fact 
that  every  part  of  its  area  is  supplied  by  more  than  one  nerve  and  that  the 
blood  vessels  anastomose  very  freely  together,  should  next  convince  himself 
of  the  greater  looseness  of  the  areolar  layer  beneath  the  galea  in  the  medial 
area  and  its  greater  denseness  and  closer  attachment  to  the  various  parts 
of  the  superjacent  epicranius,  and  the  subjacent  pericranium  at  the  margins 
of  the  scalp  area.  He  may  do  this  by  introducing  the  handle  of  a  scalpel 
through  a  median  incision  in  the  galea,  and  passing  it  anteriorly  and 
posteriorly  and  from  side  to  side. 

The  Layer  of  Loose  Areolar  Tissue. — This  is  the  fourth 
layer  of  the  scalp.  It  is  but  shghtly  vascular  and  is  of  loose 
texture,  but  is  not  equally  loose  over  the  whole  area  of  the 
scalp  ;  on  the  contrary  in  the  regions  of  the  temporal  and 
supra-orbital  ridges  it  becomes  much  denser,  and,  at  the  same 
time,  much  more  closely  connected  with  the  galea  aponeurotica 
and  the  frontalis  muscles,  whilst  posteriorly  it  disappears 
where  the  occipitalis  muscles  and  the  galea  become  attached 
to  the  superior  nuchal  lines.  It  is  on  account  of  these 
peculiarities  that  effusions  of  blood  or  inflammatory  exudations 
in  the  areolar  layer  easily  raise  the  greater  part  of  the  scalp 
from  the  bone,  but  such  effusions  do  not  readily  pass  from 
beneath  the  scalp  into  either  the  facial,  temporal,  or  occipital 
regions. 

On  the  fifth  day  after  the  body  has  been  placed  upon  its 
back,  the  eighth  after  it  was  brought  into  the  room,  the 
dissector  of  the  head  and  neck  must  assist  the  dissector  of 
the  upper  extremity  to  display  the  whole  extent  of  the  brachial 
plexus  and  the  origins  of  the  branches  which  spring  from  it ; 
and  he  should  take  the  opportunity  to  revise  his  own  know- 
ledge of  the  plexus.  Detach  the  clavicular  head  of  the 
sterno-mastoid  from  the  clavicle,  and  displace  the  sternal 
head  towards  the  median  plane.  When  this  has  been  done 
the  anterior  and  upper  parts  of  the  sterno-clavicular  joint 
capsule  will  be  fully  exposed,  for  the  pectoraHs  major,  which 
covered  the  lower  part  of  the  anterior  surface,  has  already 
been  reflected  by  the  dissector  of  the  upper  extremity. 

Dissection. — The  sterno-clavicular  joint  is  described  on  p.  28  of  Vol.  I. 
After  the  dissectors  have  noted  that  the  fibres  of  the  capsule  run  medially 
and  downwards  from  the  clavicle  to  the  sternum,  the  anterior,  superior, 
and  posterior  portions  must  be  divided  close  to  the  sternum,  care  being 
taken  to  avoid  injury  to  the  anterior  jugular  vein,  which  passes  laterally 
close  to  the  upper  and  back  part  of  the  joint.  When  the  division  is 
completed,   elevate    the   sternal    end    of  the   clavicle   by    depressing    the 


i6o  HEAD  AND  NECK 

acromial  end,  introduce  the  knife  into  the  cavity  of  the  joint,  close 
to  the  sternum,  and  carry  it  laterally  below  the  clavicle,  to  detach 
the  lower  part  of  the  interarticular  cartilage  from  the  sternum  and 
the  cartilage  of  the  first  rib,  and  to  divide  the  lower  part  of  the  capsule 
and  the  costo-clavicular  ligament,  which  lies  immediately  lateral  to  it.  If 
the  subclavius  muscle  has  not  already  been  detached,  it  also  must  be  divided, 
and  then  the  clavicle  can  be  displaced  laterally,  and  the  whole  extent  of 
the  plexus  will  be  exposed. 

The  Brachial  Plexus. — The  brachial  plexus  is  fully  described  on  p.  28, 
Vol.  I.,  and  only  a  brief  resume  of  the  main  facts  regarding  it  is  given  here. 
The  plexus  is  formed  by  the  last  four  cervical  nerves  and  the  larger  part 
of  the  first  thoracic  nerve ;  it  also  receives  a  communication  from  the  fourth 
cervical  nerve  and  not  uncommonly  a  small  twig  from  the  second  thoracic 
nerve.  These  various  nerves  constitute  the  7'oots  of  the  plexus.  The  roots 
of  the  plexus  emerge  from  between  the  scalenus  medius  and  the  scalenus 
anterior,  and  unite  to  form  three  trunks,  upper,  middle,  and  lower,  which 
lie  superficial  to  the  scalenus  medius,  the  lowest  of  the  three  being  wedged  in 
between  that  muscle  posteriorly  and  the  third  part  of  the  subclavian  artery 
anteriorly.  The  tipper  trunk  is  formed  by  the  fifth  and  sixth  nerves  and  the 
communication  from  the  fourth.  The  seventh  nerve  alone  forms  the  middle 
trunk  ;  and  the  lowest  trunk  is  formed  by  the  eighth  cervical  and  first 
thoracic  nerves  and  the  communication  from  the  second  thoracic.  Almost 
immediately  after  their  formation  the  trunks  divide  into  anterior  and 
posterior  divisions,  and  the  divisions  reunite  to  form  three  cords,  lateral, 
medial,  and  posterior.  The  lateral  cord  is  formed  by  the  anterior  divisions 
of  the  upper  and  middle  trunks,  the  medial  cord  by  the  anterior  division  of 
the  lowest  trunk,  and  all  three  posterior  divisions  unite  to  form  Xhe  posterior 
cord.  The  cords  descend  behind  the  clavicle  and  subclavius  muscle, 
through  the  cervico-axillary  canal,  to  the  level  of  the  coracoid  process  of 
the  scapula  where  the  plexus  terminates  and  each  cord  divides  into  two 
terminal  branches.  The  terminal  branches  of  the  lateral  cord  are  the 
lateral  head  of  the  median  nerve  and  the  musculo-cutaneous  nerve.  Those 
of  the  medial  cord  are  the  medial  head  of  the  median  and  the  ulnar  nerve, 
and  the  posterior  cord  divides  into  the  axillary  (O.T.  circumflex)  nerve 
and  the  radial  (O.T.  musculo-spiral).  In  addition  to  the  terminal  branches, 
collateral  branches  are  given  off  from  the  roots,  the  trunks  and  the  cords  ; 
and  the  roots  are  connected  with  the  middle  and  lower  ganglia  of  the 
cervical  part  of  the  sympathetic  trunk  by  grey  rami  communicantes.  The 
branches  given  oft'  from  the  roots  are  twigs  of  supply  to  the  longus  colli, 
the  scalenus  anterior,  the  scalenus  medius,  and  the  scalenus  posterior,  the 
roots  of  origin  of  the  long  thoracic  nerve,  which  supplies  the  serratus  anterior 
(O.T.  magnus)  and  the  dorsal  scapular  nerve  (O.T.  nerve  to  the  rhomboids). 
The  roots  of  the  long  thoracic  nerve  spring  from  the  fifth,  sixth,  and  seventh 
nerves  ;  the  upper  two  pierce  the  scalenus  medius  and  the  lowest  passes 
anterior  to  that  muscle.  The  three  unite,  behind  the  trunks  of  the  plexus, 
to  form  the  stem  of  the  nerve,  which  descends  behind  the  cords  of  the 
plexus  into  the  axilla.  The  dorsalis  scapulae  nerve  arises  from  the  lateral 
border  of  the  fifth  nerve  ;  it  disappears  under  cover  of  the  levator  scapulae 
and  supplies  the  two  rhomboid  muscles,  and,  sometimes,  the  levator  scapulae. 

The  branches  from  the  trunks  of  the  plexus  are  the  suprascapular  nerve 
and  the  nerve  to  the  subclavius.  They  both  spring  from  the  upper  trunk. 
The  collateral  branches  of  the  three  cords  of  the  plexus,  are  ( i )  from  the 
outer  cord  :  the  lateral  anterior  thoracic  nerve  ;  (2)  from  the  posterior  cord  : 
the  upper  and  lower  subscapular  nerves  and  the  thoraco-dorsal  nerve 
(O.T.  long  subscapular) ;  and  (3)  from  the  medial  cord  :  the  medial  anterior 
thoracic,  the  medial  cutaneous  nerve    of  the    arm   (O.T.   lesser  internal 


THE  DISSECTION  OF  THE   BACK  i6i 

cutaneous)  and  the  medial  cutaneous  nerve  of  the  forearm  (O.T.  internal 
cutaneous). 

The  Position  of  the  Brachial  Plexus.  — The  plexus  lies  in  the  lower  and 
anterior  part  of  the  posterior  triangle  of  the  neck,  partly  above  and  partly 
below  the  posterior  belly  of  the  omo-hyoid  ;  posterior  to  the  clavicle  ;  and 
in  the  axilla.  Above  the  clavicle  it  is  covered  by  the  skin,  the  superficial 
fascia  and  the  platysma,  branches  of  the  supraclavicular  nerves,  the  first 
layer  of  deep  fascia,  the  external  jugTilar  vein,  and  the  terminal  parts  of  the 
transverse  cervical  and  transverse  (supra)  scapular  veins ;  the  second 
layer  of  deep  cervical  fascia,  the  transverse  cervical  artery,  the  posterior 
belly  of  the  omo-hyoid,  the  nerve  to  the  subclavius,  and  the  third  part  of 
the  subclavian  artery.  Behind  the  clavicle  it  is  crossed  superficially  by 
the  transverse  scapular  artery  (O.T.  suprascapular).  Below  the  clavicle  it 
is  covered  by  the  skin  and  superficial  fascia,  the  platysma,  the  middle 
supracla\acular  nerves,  the  deep  fascia,  the  pectoralis  major,  the  pectoralis 
minor,  the  cephalic  vein,  the  branches  of  the  thoraco-acromial  artery,  the 
costo-coracoid  membrane,  and  the  axillary  arter}^  and  vein. 

Its  posterior'  relations  in  the  neck  are  the  scalenus  medius  and  the  long 
thoracic  nerve.  In  the  axilla  the  serratus  anterior,  the  fat  in  the  interval 
between  the  serratus  anterior  and  the  subscapularis,  and  finally  the  sub- 
scapularis  itself. 

After  the  brachial  plexus  has  been  examined,  the  clavicle  must  be 
replaced  in  position  and  the  skin  flap,  reflected  from  the  posterior  triangle, 
must  be  replaced  and  fixed  in  position  by  a  few  sutures. 

On  the  ninth  day  after  the  body  is  brought  into  the  room, 
that  is,  on  the  sixth  day  after  it  has  been  placed  on  its  back, 
it  will  be  turned  upon  its  face,  with  the  thorax  and  the  pelvis 
supported  by  blocks.  The  body  will  remain  upon  its  face  for 
five  days,  and  during  that  period  the  dissectors  of  the  head 
and  neck  must  complete  the  dissection  of  the  posterior  part 
of  the  scalp ;  dissect  the  muscles,  vessels  and  nerves  of  the 
back  and  the  suboccipital  region ;  and  remove  and  examine 
the  spinal  medulla. 


THE    DISSECTION    OF    THE    BACK. 

Dissection. — Make  a  median  longitudinal  incision  from  the  external 
occipital  protuberance  to  the  seventh  cervical  spine,  and  a  second  laterally 
from  the  seventh  cervical  spine  to  the  acromion,  and  throw  the  flap  laterally. 
When  this  has  been  done  the  posterior  triangle  will  be  exposed  from  behind, 
and  the  dissector  should  take  the  opportunity  of  noting  the  positions  of  the 
contents  and  the  constituent  parts  of  the  floor  from  this  aspect.  Afterwards 
he  must  look  for  the  superficial  nerves  in  the  superficial  fascia  over  the 
upper  part  of  the  trapezius.  If  the  great  occipital  nerve  was  not  found 
during  the  dissection  of  the  scalp  secure  it  at  once,  as  it  pierces  the  deep 
fascia  covering  the  upper  end  of  the  trapezius,  about  midway  between  the 
external  occipital  protuberance  and  the  posterior  border  of  the  mastoid 
portion  of  the  temporal  bone  ;  trace  it  upwards  through  the  dense  superficial 
fascia  of  the  scalp  and  clean  the  branches  of  the  occipital  artery  which  are 
distributed  in  the  same  region.  The  smallest  occipital  nerve  will  be  found 
VOL.   II — 11 


1 62  HEAD  AND  NECK 

in  the  superficial  fascia  between  the  great  occipital  and  the  median  plane. 
It  is  the  medial  division  of  the  posterior  branch  of  the  third  cervical  nerve, 
and  it  supplies  the  skin  of  the  medial  and  lower  part  of  the  posterior  portion 
of  the  scalp<i^nd  the  adjacent  part  of  the  skin  of  the  back  of  the  neck. 
Trace  it  upwards  to  its  termination  and  downwards  to  the  point  where  it 
pierces  the  deep  fascia  covering  the  trapezius.  At  a  still  lower  level  look 
for  the  medial  divisions  of  the  posterior  branches  of  the  other  cervical 
nerves.  They  are  variable  in  number  and  position,  but  those  which  are 
present  will  be  found  piercing  the  deep  fascia  over  the  trapezius,  at  a  short 
distance  from  the  median  plane,  and  running  downwards  and  laterally 
towards  the  posterior  triangle. 

After  the  cutaneous  nerves  have  been  found  remove  the  remains  of  the 
superficial  fascia  and  the  deep  fascia  from  the  surface  of  the  trapezius. 

The  Terminal  Part  of  the  Great  Occipital  Nerve. — The 

great  occipital  nerve  is  the  large  medial  division  of  the 
posterior  branch  of  the  second  cervical  nerve.  It  enters  the 
posterior  part  of  the  scalp,  after  piercing  the  upper  part  of  the 
trapezius  and  the  deep  fascia  of  the  back  of  the  neck,  and 
ramifies  in  the  superficial  fascia  of  the  scalp  over  the  occipital 
bone  and  the  posterior  part  of  the  parietal  bone,  accompanying 
the  branches  of  the  occipital  artery,  and  communicating  with 
the  great  auricular  and  small  occipital  nerves. 

Arteria  Occipitalis. — After  emerging  from  between  the 
trapezius  and  the  sterno-mastoid,  at  the  apex  of  the  posterior 
triangle,  or  piercing  the  upper  part  of  the  trapezius,  the  terminal 
part  of  the  occipital  artery  passes  through  the  deep  fascia  of 
the  back  of  the  neck  and  enters  the  superficial  fascia  of  the 
posterior  part  of  the  scalp.  It  anastomoses  with  its  fellow  of 
the  opposite  side,  and  with  the  posterior  auricular  and  the 
superficial  temporal  arteries.  As  a  rule,  it  breaks  up  into  two 
main  branches,  a  lateral  and  a  medial.  The  medial  branch 
gives  off  cutaneous  twigs  and  a  meningeal  branch,  which  passes 
through  the  parietal  foramen  and  anastomoses  with  a  branch 
of  the  middle  meningeal  artery.  Through  the  same  foramen, 
passes  an  emissary  vein  which  connects  the  occipital  veins 
with  the  superior  sagittal  (longitudinal)  sinus. 

Musculus  Trapezius. — The  trapezius  and  latissimus  dorsi 
constitute  the  first  layer  of  the  muscles  of  the  back.  Only 
that  part  of  the  trapezius  which  lies  above  the  level  of  the 
seventh  cervical  spine  belongs  to  the  dissector  of  the  head  and 
neck ;  the  lower  part  and  the  latissimus  must  be  cleaned  by 
the  dissector  of  the  arm,  but  the  dissector  of  the  head  should 
take  the  opportunity  to  revise  his  knowledge  of  the  whole 
origin  and  insertion  of  the  muscle.  It  arises  from  the  medial 
third    of   the    superior    nuchal    line   of   the   occipital    bone, 


THE  DISSECTION  OF  THE  BACK 


163 


the  external  occipital  protuberance,  the  whole  length  of  the 
ligamentum  nuchae,  the  seventh  cervical  spine,  the  tips  of 
all  the  thoracic  spines  and  the  corresponding  supraspinous 
ligaments. 

In  the  region  of  the  seventh  cervical  spine  the  origin  is  more  aponeurotic 
than  elsewhere,  and  the  fine  tendinous  fibres  of  the  muscles  of  the  two  sides 
form  an  ovoid  aponeurotic  area  some  two  inches  in  length. 


Galea 
aponeurotica 


Great  occipital 
nerve 


Occipital  artery 


Third  occipital 


nerve     ^ 


Trapezius 


Occipital  belly  of 
epicranius 

Semispinalis  capitis 
(O.T.  complexus) 

Posterior 
auricular  muscle 

Splenius  capitis 

Posterior 
auricular  nerve 

Parotid  gland 
Small  occipital  nerve 
Sterno-mastoid 
Great  auricular  nerve 

Levator  scapulae 


Fig.  70. — Superficial  dissection  of  the  Back  of  the  Neck. 


The  upper  fibres  of  the  muscle  descend  in  oblique  curves 
and  are  inserted  into  the  lateral  third  of  the  posterior  border 
and  the  adjacent  part  of  the  superior  surface  of  the  clavicle ; 
the  intermediate  fibres  run  horizontally,  towards  the  shoulder, 
and  are  inserted  into  the  medial  border  of  the  acromion  and 
the  upper  lip  of  the  posterior  border  of  the  spine  of  the 
scapula.  The  lower  fibres  ascend,  and  terminate  in  a  small 
II — 11  a 


1 64  HEAD  AND  NECK 

triangular  tendon  which  plays  over  the  smooth  triangle  at  the 
root  of  the  scapular  spine  and  is  inserted  partly  into  the  lower 
and  partly  into  the  upper  lip  of  the  spine.  The  muscle  is 
supplied  by  the  accessory  and  the  third  and  fourth  cervical 
nerves.  It  draws  the  scapula  medially  and  braces  the  shoulder 
backwards,  raises  the  tip  of  the  shoulder,  or  depresses  the 
scapula  and  turns  the  glenoid  fossa  upwards  according  to 
whether  the  intermediate,  the  upper,  or  the  lower  fibres  are 
mainly  in  action. 

Dissection. — On  the  second  day  after  the  subject  has  been  placed  on  its 
face,  the  trapezius  may  be  reflected.  This  must  be  done  in  conjunction 
with  the  dissector  of  the  arm.  First  separate  the  muscle  from  the  occipital 
bone,  and  then  divide  it  about  half  an  inch  from  the  spines  of  the  vertebrae. 
The  muscle  can  now  be  raised  and  thrown  laterally  towards  its  insertion. 
On  its  deep  surface  the  accessory  nerve,  the  twigs  of  supply  from  the  third 
and  fourth  cervical  nerves  and  the  superficial  cervical  artery  will  be  noticed. 
It  is  the  duty  of  the  dissector  of  the  upper  limb  to  dissect  these,  but  the 
dissector  of  the  head  and  neck  should  trace  the  superficial  cervical  artery 
to  its  origin  from  the  transversa  colli. 

The  attachments  of  the  levator  scapulae  also  must  be  defined.  Two 
twigs  from  the  third  and  fourth  cervical  nerves,  which  lie  on  its  surface 
and  finally  enter  its  substance,  have  already  been  secured.  Further, 
passing  downwards  under  cover  of  this  muscle,  the  dorsal  scapular  nerve 
(O.T.  nerve  to  the  rhomboids)  and  the  descending  branch  (O.T.  posterior 
scapular)  of  the  transversa  colli  artery  will  be  found.  Almost  invariably 
the  dorsal  scapular  nerve  gives  one  or  two  twigs  to  the  levator  scapulae. 

The  levator  scapulae,  the  rhomboids,  the  posterior  serrati  and  the  splenius 
are  classed  as  muscles  of  the  second  layer.  The  rhomboids  and  the  lower 
part  of  the  levator  belong  to  the  dissector  of  the  arm  ;  the  remaining  muscles 
are  the  property  of  the  dissector  of  the  head  and  neck. 

Musculus  Levator  Scapulse. — This  muscle  arises  by  four 
slips  from  the  posterior  parts  of  the  transverse  processes  of 
the  upper  four  cervical  vertebrae.  These  unite  to  form  an 
elongated  muscle  which  extends  downwards  and  posteriorly  to 
be  inserted  into  that  portion  of  the  vertebral  border  of  the 
scapula  which  is  placed  above'  the  root  of  the  spine.  Its 
nerve-supply  comes  from  the  third  and  fourth  cervical  nerves, 
and  also  from  the  dorsal  scapular  nerve. 

The  origin  of  the  posterior  belly  of  the  omo-hyoid  muscle 
may  now  be  examined.  It  is  attached  to  the  upper  transverse 
ligament  of  the  scapula  and  the  adjacent  part  of  the  superior 
border  of  the  bone.  The  transverse  scapular  artery  (O.T. 
suprascapular)  will  be  noticed  passing  over  the  upper  trans- 
verse ligament  whilst  the  suprascapular  nerve  traverses  the 
notch  below  it. 

The  second  day's  work   is  now  completed,   and  on  the  same  day  the 


THE  DISSECTION  OF  THE  BACK 


165 


dissector  of  the  upper  limb  must  finish  his  share  of  the  dissection  of  the 
back,  so  as  to  allow  the  dissector  of  the  head  and  neck  to  begin  the 
examination  of  the  deeper  structures  on  the  dorsal  aspect  of  the  trunk. 

Three  days  are  allowed  for  this  dissection,  and  these  may  be  disposed 
of  in  the  following  manner  :— On  the  first  day,  all  the  muscles,  fasciae, 
nerves,  and  blood  vessels  of  the  back,  with  the  exception _  of  those  in 
connection  with  the  sub -occipital  triangle,  should  be  studied;  on  the 
second  day,  the  sub-occipital  triangle  must  be  examined  ;  and  on  the  third 
day  the  medulla  spinalis  (O.T.  spinal  cord)  must  be  displayed. 

Musculi  Serrati  Posteriores. — These  are  two  thin  sheets 
of  fleshy  fibres,  which  are  placed  upon  the  posterior  aspect 


Serratus 
post.  inf. 


Latissimus 
dorsi 


Transversus 

abdominis 

Internal 

oblique' 

External 

oblique 

Fascia 
transversalis' 


c Ilio-costalis 


Quadratus 
lumborum 


Psoas  major 


Fig.  71. Diagram  to  show  the  Connections  of  the  Lumbo-dorsal  Fascia. 

of  the  thoracic  wall.  The  serratus  posterior  superior  is  much 
the  smaller  of  the  two  \  it  arises  by  a  thin  aponeurotic  tendon 
from  the  lower  part  of  the  ligamentum  nuchse;  from  the  spinous 
process  of  the  seventh  cervical,  vertebra ;  and  from  the  spinous 
processes  of  the  upper  two  or  three  thoracic  vertebrae.  It 
passes  obliquely  downwards  and  laterally,  and  is  inserted  into 
the  outer  surfaces  of  the  second,  third,  fourth,  and  fifth  ribs, 
a  short  distance  anterior  to  their  angles. 

The  serratus  posterior  inferior  will  be  brought  into  view  by 
raising  and  throwing  medially  that  portion  of  the  latissimus 
dorsi  which  the  dissector  of  the  upper  limb  has  left  attached 
to  the  lumbo-dorsal  fascia.  It  takes  origin  from  the  spinous 
processes    of   the    last  two   thoracic   and   upper  two  lumbar 


1 66  HEAD  AND  NECK 

vertebrae,  and  the  supraspinous  ligaments  between  them. 
The  dissector  will  note,  however,  that  this  is  not  an  indepen- 
dent and  distinct  attachment,  but  that  it  is  effected  through 
the  medium  of  the  lumbo- dorsal  fascia,  with  which  the 
aponeurotic  tendon  of  the  muscle  blends.  The  muscle 
passes  upwards  and  laterally  and  is  inserted  into  the  outer 
surfaces  of  the  lower  four  ribs. 

Fascia  Lumbo-dorsalis. — On  the  third  day  after  the  body 
is  placed  upon  its  face  the  dissector  of  the  head  and  neck 
should  associate  himself  with  the  dissector  of  the  abdomen 
in  the  examination  of  the  lumbo-dorsal  fascia.  It  is  an 
aponeurotic  layer,  thin  in  the  thoracic  portion  of  its  extent, 
but  thick  and  strong  in  the  lumbar  and  sacral  regions ;  and 
in  all  these  regions  it  binds  down  the  muscles  of  the  back 
to  the  sides  of  the  spinous  processes  and  to  the  transverse 
processes  of  the  vertebrae. 

The  Dorsal  Part  of  the  Lumbo-dorsal  Fascia  (O.T.  Vertebrav 
Aponeurosis). — This  part  of  the  lumbo-dorsal  fascia  is  a  thin 
transparent  lamina  which  extends  from  the  tips  of  the  spines 
and  the  supraspinous  ligaments  to  the  angles  of  the  ribs. 
At  the  upper  end  of  the  thoracic  region  it  dips  beneath  the 
serratus  posterior  superior  into  the  neck,  and  at  the  lower 
end  it  blends  with  the  aponeurosis  of  origin  of  the  serratus 
posterior  inferior,  and  through  that  becomes  continuous  with 
the  posterior  layer  of  the  lumbar  portion. 

Dissection. — To  display  the  lumbar  part  of  the  lumbo-dorsal  fascia  clear 
away  the  remains  of  the  origin  of  the  latissimus  dorsi,  which  springs  from 
its  posterior  surface,  and  then  reflect  the  serratus  posterior  inferior  by 
cutting  through  it  at  right  angles  to  its  fibres  and  turning  it  medially  and 
laterally  towards  its  origin  and  insertion.  As  the  lateral  part  is  turned 
aside  secure  its  nerves  of  supply,  which  are  derived  from  the  lower  inter- 
costal nerves,  and  enter  its  deep  surface.  Next  remove  the  remains  of  the 
origin  of  the  serratus  posterior  inferior,  and  then  the  posterior  layer  of  the  ■ 
lumbar  part  of  the  lumbo-dorsal  fascia  will  be  completely  exposed. 

The  Lumbar  Part  of  the  Lumbo-dorsal  Fascia. — This  portion 
of  the  lumbo-dorsal  fascia  is  separable  into  three  lamellae,  a 
posterior,  a  middle,  and  an  anterior.  All  three  fuse  together 
laterally,  where  they  become  connected  with  the  internal 
oblique  and  the  transversus  abdominis  muscles.  ThQ  posterior 
layer,  which  is  the  strongest  of  the  three,  is  a  dense  tendinous 
aponeurosis.  It  is  continuous  above  with  the  thoracic  part. 
Below,  it  is  attached  to  the  posterior  part  of  the  lateral  lip  of 
the  iliac  crest,  and  to  the  dorsum  of  the  sacrum  and  the  coccyx. 


THE  DISSECTION  OF  THE  BACK  167 

Medially^  it  is  attached  to  the  tips  of  the  spines  of  the  lumbar 
vertebrae  and  the  sacrum  ;  and  laterally  it  blends  ^vith  the 
posterior  surface  of  the  middle  lamella  (Fig.  71).  The 
aponeurosis  of  origin  of  the  latissimus  dorsi  and  the  serratus 
posterior  inferior  arise  from  its  posterior  surface. 

Dissection. — Make  a  longitudinal  incision  through  the  posterior  layer  of 
the  lumbar  part  of  the  lumbo-dorsal  fascia,  midway  between  its  medial 
and  its  lateral  borders.  At  each  end  of  the  longitudinal  incision  make  a 
transverse  incision  extending  from  the  spine  medially  to  the  lateral  border 
of  the  rounded  mass  of  spinal  muscles  lying  under  cover  of  the  fascia. 
Turn  the  medial  part  of  the  divided  fascia  towards  the  median  plane,  and 
verify  its  attachment  to  the  vertebral  spines  and  the  supraspinous  ligaments. 
Pull  the  lateral  part  aside,  and  at  the  lateral  border  of  the  mass  of  posterior 
spinal  muscles  it  will  be  found  to  blend  with  a  deeper  layer,  the  middle 
lamella.  Push  the  mass  of  posterior  spinal  muscles  towards  the  median 
plane,  and  follow  the  middle  lamella  of  the  fascia  to  its  attachment. 

The  middle  lamella  is  attached  medially  to  the  tips  of  the 
transverse  processes  of  the  lumbar  vertebrae ;  below  to  the 
iliac  crest,  and  above  to  the  last  rib.  Laterally  it  blends 
with  the  posterior  and  anterior  lamellae,  and  immediately 
lateral  to  its  line  of  union  with  the  posterior  lamella  the 
internal  oblique  arises  from  its  posterior  surface.  To  expose 
it  thoroughly  the  mass  of  posterior  spinal  muscles  must  be 
pushed  medially. 

Dissection. — After  the  middle  lamella  has  been  examined  divide  it 
longitudinally,  close  to  its  attachment  to  the  tips  of  the  transverse  processes, 
and  transversely  along  the  line  of  the  iliac  crest,  and  turn  it  laterally.  A 
considerable  part  of  the  posterior  surface  of  the  quadratus  lumborum 
muscle  will  then  be  exposed.  Displace  the  lateral  border  of  the  quadratus 
lumborum  towards  the  median  plane,  and  the  anterior  lamella  of  the 
lumbar  part  of  the  lumbo-dorsal  fascia  will  be  brought  into  view. 

The  anterior  lamella  of  the  lumbar  part  of  the  lumbo- 
dorsal  fascia  is  attached  medially  to  the  anterior  surfaces  of 
the  roots  of  the  transverse  processes  of  the  lumbar  vertebrae  ; 
laterally  it  blends  with  the  fused  middle  and  posterior  lamellae 
to  form  the  common  aponeurosis  of  origin  of  the  transversus 
abdominis  muscle,  and  it  is  by  means  of  the  three  lamellae 
of  the  lumbar  fascia  that  the  latter  muscle  arises  from  the  tips 
of  the  spines,  and  the  tips  and  the  roots  of  the  transverse 
processes  of  the  lumbar  vertebrae.  The  upper  border  of  the 
anterior  lamella  becomes  thickened,  and  extends  anterior  to 
the  quadratus  lumborum  from  the  last  rib  to  the  trans- 
verse process  of  the  first  lumbar  vertebra  as  the  arcus 
lumbo-costalis  lateralis  (O.T.  external  arcuate  ligament) ;  the 
II— 11& 


1 68  HEAD  AND  NECK 

lower  border  blends  with  the  ilio-lumbar  ligament.  The 
dissector  should  verify  these  various  attachments  by  passing 
his  fingers  over  the  posterior  surface  of  the  lamella  from  its 
lateral  to  its  medial  border,  and  from  its  upper  to  its  lower  end. 

Dissection. — After  satisfying  himself  regarding  the  lamellae  of  the  lumbar 
part  of  the  lumbo-dorsal  fascia  and  their  relations  to  the  posterior  spinal 
muscles,  to  the  quadratus  lumborum,  and  to  the  internal  oblique  and  the 
transversus  abdominis  muscles,  the  dissector  should  make  a  longitudinal 
incision  through  the  anterior  lamella,  and  the  peri-renal  fascia  anterior  to  it ; 
and,  introducing  his  finger  through  the  opening  into  the  extra-peritoneal 
fatty  tissue,  he  should  scrape  away  the  latter  until  he  exposes  the  kidney, 
below  the  level  of  the  last  rib,  and  the  adjacent  part  of  the  colon,  which 
lies  along  the  lower  and  lateral  part  of  the  kidney.  After  this  has  been 
done  he  should  reflect  the  serratus  posterior  superior  and  secure  its  nerves 
of  supply  which  spring  from  the  upper  intercostal  nerves  and  enter  its  deep 
surface  ;  then  he  should  remove  the  thoracic  part  of  the  lumbo-dorsal  fascia 
and  commence  the  study  of  the  posterior  spinal  muscles,  beginning  with 
the  splenius. 

Musculus  Splenius. — The  splenius  has  a  continuous  origin 
from  the  lower  half  of  the  ligamentum  nuchse,  and  from  the 
spines  of  the  seventh  cervical  and  upper  six  thoracic  vertebrae. 
Its  fibres  pass  obliquely  upwards  and  laterally,  forming  a  thick 
fiat  muscle,  which  soon  divides  into  a  cervical  and  a  cranial 
portion,  termed  respectively  the  splenius  cervicis  and  the 
splenius  capitis. 

The  splenius  cervicis  turns  anteriorly  and  is  inserted  by 
tendinous  slips  into  the  tubercles  of  the  transverse  processes 
of  the  upper  two  or  three  cervical  vertebrae,  medial  to  the 
levator  scapulae. 

The  splenius  capitis  passes  under  cover  of  the  upper  part 
of  the  sterno-mastoid  muscle,  and  gains  insertion  into  the 
lower  part  of  the  mastoid  portion  of  the  temporal  bone  and 
into  the  lateral  portion  of  the  superior  nuchal  line  of  the 
occipital  bone.  To  see  this  insertion,  the  sterno-mastoid 
muscle  may  be  divided  along  the  superior  nuchal  line,  but 
it  must  not  be  detached  from  the  temporal  bone. 

Dissection. — The  deeper  spinal  muscles  must  now  be  dissected.  Begin 
by  reflecting  the  splenius  muscle.  Detach  it  from  its  origin  and  throw 
it  laterally  and  upwards  towards  its  insertion.  Whilst  doing  this,  preserve 
the  cutaneous  branches  of  the  cervical  nerves  which  pierce  it. 

When  the  splenius  capitis  is  fully  reflected,  a  small  triangular  space 
will  be  noticed  close  to  the  superior  nuchal  line  of  the  occipital  bone. 
Anteriorly,  it  is  bounded  by  the  longissimus  capitis  (O.T.  trachelo-mastoid)  ; 
posteriorly,  by  the  lateral  border  of  the  semispinalis  capitis  (O.T.  com- 
plexus) ;  and  above,  by  the  superior  nuchal  line  of  the  occipital  bone. 
The  floor  of  this  little  space  is  formed  by  the  superior  oblique  muscle  of 


THE  DISSECTION  OF  THE  BACK  169 

the  head,  and  it  is  traversed  by  the  occipital  artery,  which  in  this  part  of 
its  course  gives  off  its  descending  branch  (O.T.  arteria  princeps  cervicis), 
and  its  meningeal  branch. 

The  Third  Layer  of  Muscles. — Under  this  head  are  included  a  series 
of  muscular  strands  which  stretch  with  a  greater  or  less  degree  of  continuity 
along  the  entire  length  of  the  dorsal  aspect  of  the  vertebral  column.  In  the 
lumbar  region  they  constitute  a  bulky  fleshy  mass  which  may  be  considered 
the  main  starting-point.  This  mass  is  the  musculus  sacro-spinalis  which 
has  the  following  origins  : — (i)  from  the  spines  of  all  the  lumbar  vertebrae  ; 

(2)  from  the  supraspinous  ligaments  which  bind  the  lumbar  spines  together  ; 

(3)  from  the  dorsum  of  the  sacrum  and  from  the  posterior  sacro-iliac  liga- 
ment ;  (4)  from  the  posterior  fifth  of  the  iliac  crest ;  (5)  from  the  deep 
surface  of  the  posterior  layer  of  the  lumbo-dorsal  fascia.  In  great  part  the 
superficial  surface  of  this  muscular  mass  is  covered  by  and  is  adherent  to 
the  posterior  layer  of  the  lumbo-dorsal  fascia. 

Superiorly  the  sacro-lumbalis  divides  into  three  columns.  The  lateral 
column  first  separates  from  the  general  mass,  and  to  it  the  name  of  ilio- 
costalis  is  given  ;  the  middle  column  is  termed  the  loiigissinnis,  and  the 
medial  column,  which  becomes  quite  distinct  only  as  the  upper  part  of  the 
dorsal  region  is  approached,  is  called  the  spinalis.  The  semispinalis  muscle 
is  also  included  in  the  third  layer. 

The  Ilio-costalis  is  a  column  of  muscular  bundles  which  extends  from 
the  lumbar  to  tiie  cervical  region.  It  is  separable  into  three  segments 
known,  from  below  upwards,  as  the  ilio-costalis  lumborum,  the  ilio-costalis 
dorsi,  and  the  ilio-costalis  cervicis. 

Ilio-costalis  Lumborum. — This  muscle  and  the  longissimus  dorsi  become 
distinct  at  the  level  of  the  last  rib,  and  the  interval  between  them  is  marked 
by  the  exits  of  the  lateral  divisions  of  the  posterior  branches  of  lower 
thoracic  nerves. 

The  muscle  ends  above  in  a  series  of  six  or  sev^en  slender  tendons,  which 
are  inserted  into  the  angles  or  the  corresponding  parts  of  the  lower  six  or 
seven  ribs. 

The  Ilio-costalis  Dorsi  (O.T.  Musculus  Accessonus)  arises  by  six  or  seven 
slender  tendons  from  the  angles  of  the  lower  ribs,  on  the  medial  sides  of  the 
tendons  of  insertion  of  the  ilio-costalis  lumborum,  and  it  is  inserted  by  a 
series  of  similar  tendons  into  the  angles  of  the  upper  six  ribs  and  to  the 
transverse  process  of  the  seventh  cervical  vertebra. 

The  Ilio-costalis  Cei-vicis  (O.T.  Cervicalis  Ascendens). — This  highest 
segment  of  the  ilio-costalis  arises,  on  the  medial  side  of  the  ilio-costalis 
dorsi,  by  four  slips  which  spring  from  the  third,  fourth,  fifth,  and  sixth  ribs  ; 
it  is  inserted  into  the  transverse  processes  of  the  fourth,  fifth,  and  sixth 
cervical  vertebrae. 

To  display  the  ilio-costalis  properly,  the  dissector  should  first  evert  the 
lowest  segment,  and  then  in  turn  the  middle  and  upper  segments,  but 
whilst  doing  this  he  must  take  care  to  preserve  the  lateral  divisions  of  the 
posterior  branches  of  the  spinal  nerves. 

The  Longissimus  is  the  middle  and  largest  of  the  three  muscle  columns. 
It  extends  upwards,  through  the  thoracic  and  cervical  regions,  to  the  head, 
and  it  also  is  separable  into  three  segments  :  longissimus  dorsi,  longissimus 
cervicis,  and  longissimus  capitis.  The  interval  between  the  longissimus 
and  the  spinalis  is  frequently  difficult  to  define,  but  if  the  fascia  is  carefully 
cleaned  from  the  lateral  to  the  medial  border  of  the  longissimus  in  the 
upper  thoracic  region,  the  separation  will  become  apparent,  and  after  it 
has  been  found  the  attachments  of  the  longissimus  must  be  defined. 

Longissimiis  Dorsi. — The  dorsal  part  of  the  longissimus  possesses  two 
rows  of  slips  of  insertion  :    a  medial  row   of  tendinous  slips  which    are 


I70  HEAD  AND  NECK 

attached  to  the  tips  of  the  transverse  processes  of  the  thoracic  and  the 
accessory  processes  of  the  lumbar  vertebrae,  and  a  lateral  row  of  muscular 
slips  which  are  inserted  into  the  lower  ten  ribs,  on  the  lateral  sides  of  their 
tubercles,  and  to  the  transverse  processes  of  the  lumbar  vertebrae,  and  to 
the  posterior  surface  of  the  middle  lamella  of  the  lumbar  fascia. 

Loiigissimus  Cervicis  {O.T.  Transversalis  Cervicis). — This  portion  of  the 
longissimus  springs  from  the  transverse  processes  of  the  upper  four  thoracic 
vertebrae,  and  is  inserted  into  the  posterior  tubercles  of  the  transverse 
processes  of  the  cervical  vertebrae  from  the  second  to  the  sixth  inclusive. 

Longissimus  Capitis  (O.T.  Trachelo-niastoid). — The  longissimus  capitis 
lies  in  the  neck  under  cover  of  the  splenius.  It  arises  in  common  with  the 
longissimus  cervicis  from  the  transverse  processes  of  three  or  four  of  the  upper 
thoracic  vertebrae,  and,  in  addition,  from  the  articular  processes  of  a  like 
number  of  the  lower  cervical  vertebrae.  The  narrow  fleshy  band  which  results 
is  inserted  into  the  posterior  part  of  the  mastoid  portion  of  the  temporal 
bone,  under  cover  of  the  splenius  capitis  and  sterno-mastoid  muscles. 

The  Spinalis. — This  is  the  most  medial,  shortest,  and  weakest  of  the  three 
columns,  and  the  most  difficult  to  define.  Below,  it  is  intimately  blended 
with  the  longissimus  dorsi,  but  it  may  be  regarded  as  taking  origin  by  four 
tendons  from  the  spines  of  the  upper  two  lumbar  and  lower  two  thoracic 
vertebrae.  These  end  in  a  small  muscular  belly,  which  is  inserted  by  a 
series  of  slips  into  a  very  variable  number  of  the  upper  thoracic  spines. 
It  is  closely  connected  with  the  subjacent  semispinalis  dorsi. 

Spinalis  Cei^icis. — This  upward  prolongation  of  the  spinalis  is  not 
always  easy  to  define.  It  springs  from  the  spines  of  the  lower  four  cervical 
vertebrae  and  is  inserted  into  the  spines  of  the  second,  third,  and  fourth 
cervical  vertebrae. 

Dissection. — The  occipital  artery  has  already  been  seen  crossing 
the  apex  of  the  posterior  triangle  (p.  149),  and  its  terminal  branches  have 
been '  dissected  as  they  ramify  in  the  scalp  (p.  157).  The  second  part  of 
the  vessel,  which  extends  from  under  shelter  of  the  mastoid  process,  along 
the  superior  nuchal  line  of  the  occipital  bone,  to  the  point  where  it  pierces 
the  trapezius  to  become  superficial,  can  now  be  exposed  fully.  To  effect 
this,  the  longissimus  capitis  (O.T.  trachelo-mastoid)  must  be  divided  a 
short  distance  below  its  insertion,  and,  along  with  the  splenius  capitis, 
thrown  upwards  as  far  as  possible. 

Arteria  Occipitalis. — The  second  part  of  the  occipital 
artery  is  now  displayed.  In  the  region  of  the  mastoid  process 
it  is  very  deeply  placed ;  indeed,  no  less  than  five  structures 
lie  superficial  to  it.  These  are  (enumerating  them  in  order 
from  the  vessel  to  the  surface) — (i)  the  origin  of  the  posterior 
belly  of  the  digastric  muscle  ;  (2)  the  mastoid  process ;  (3) 
the  longissim.us  cervicis;  (4)  the  splenius  capitis;  and  (5) 
the  sterno-mastoid.^  As  the  artery  runs  posteriorly,  it  very 
soon  emerges  from  under  cover  of  the  first  three  of  these 
structures,  and  a  little  farther  on  it  leaves  the  shelter  of  the 
splenius,  and  is  then  covered  by  the  sterno-mastoid  alone. 
Issuing  from  under  cover  of  the  posterior  border  of  that  muscle, 

^  It  is  not  uncommon  to  find  the  artery  at  this  point  of  its  course  between 
the  splenius  and  the  longissimus  capitis. 


THE  DISSECTION  OF  THE  BACK  171 

the  artery  crosses  the  apex  of  the  posterior  triangle,  and 
disappears  under  the  trapezius,  which  it  finally  pierces  near 
the  external  occipital  protuberance,  to  reach  the  scalp.  Two 
muscles  constitute  its  deep  relations — viz.,  the  insertions  of 
the  superior  oblique  and  the  semispinalis  capitis  (O.T. 
complexus). 

The  following  branches  may  be  traced  from  this  portion  of 
the  occipital  artery  :  (i)  descending  (O.T.  arteria  princeps 
cervicis) ;  (2)  meningeal ;  (3)  muscular. 

The  ra7mcs  descendens  (O.T.  arferta  princeps  cervicis^  is  a 
twig  of  some  size,  which  passes  medially  to  the  lateral  border 
of  the  semispinalis  capitis  (O.T.  complexus) ;  there  it  divides 
into  a  superficial  and  a  deep  branch.  The  former  ramifies  on 
the  surface  of  the  semispinalis  capitis,  whilst  the  latter  sinks 
under  that  muscle,  where  it  will  be  followed  to  its  anastomosis 
with  the  deep  cervical  artery  at  a  later  stage  in  the  dissection. 

The  small  meningeal  branch  enters  the  posterior  cranial  fossa 
through  the  mastoid  foramen,  and  supplies  the  dura  mater 
and  cranial  wall  in  this  region. 

The  muscular  twigs  go  to  the  neighbouring  muscles. 

The  veins  corresponding  to  the  occipital  artery  are  two, 

or  perhaps  three,  in  number.     They  drain  the  blood  from  the 

occipital  portion  of  the  scalp,  and  open  into  the  sub-occipital 

plexus,  which  is  drained  by  the  vertebral  and  deep  cervical 

veins.      The  most  lateral  of  the  occipital  veins   frequently 

communicates  with  the  transverse  sinus  (O.T.  lateral)  through 

the  mastoid  foramen. 

Dissection. — The  semispinalis  capitis,  which  has  been  exposed  by  the 
reflection  of  the  splenius  and  the  turning  aside  of  the  longissimus  cervicis 
and  longissimus  capitis,  must  now  be  cleaned,  and  whilst  this  is  being  done 
and  its  attachments  are  being  defined,  care  must  be  taken  of  the  medial 
divisions  of  the  posterior  branches  of  the  second,  third,  fourth,  and  fifth 
cervical  nerves.  The  first  of  these— or,  in  other  words,  the  great  occipital 
— -from  its  great  size,  runs  little  risk  of  injury,  but  the  others  are  liable  to 
be  overlooked.  They  all  emerge  from  the  substance  of  the  muscle  close  to 
the  median  plane. 

Semispinalis  Capitis  (O.T.  Complexus). — The  semispinalis  capitis  is  the 
uppermost  part  of  a  muscular  column  consisting  of  three  segments,  which 
are  spoken  of  collectively  as  the  semispinalis,  and  individually  as  the  semi- 
spinalis dorsi,  the  semispinalis  cervicis,  and  the  semispinalis  capitis.  It 
belongs  to  the  third  layer  of  muscles,  of  which  the  greater  number  have 
been  dissected  already.  The  two  lower  segments  will  be  dissected  subse- 
quently, but  it  is  convenient  to  examine  the  semispinalis  capitis  at  once. 
It  is  a  thick  fleshy  mass  which  springs  by  tendinous  slips  from  the  transverse 
processes  of  the  upper  six  thoracic  vertebra;  and  the  articular  processes  of 
the  fourth,  fifth,  and  sixth  cervical  vertebrae.     Its  massive  upper  extremity 


172 


HEAD  AND  NECK 


is  inserted  into  a  somewhat  oval  area  on  the  occipital  bone,  between  the 
superior  and  inferior  nuchal  lines  close  to  the  external  occipital  crest.  It  is 
separated  from  its  fellow  muscle  of  the  opposite  side  by  the  ligamentum 
nuchae  ;  and  its  most  medial  part,  which  is  to  a  certain  extent  distinct  from 
the  general  mass,  is  divided  into  two  bellies  by  an  intermediate  tendon  and 
is  frequently  spoken  of  as  the  biventer  cervicis.  Occasionally  the  remainder 
of  the  muscle  is  also  intersected  by  a  tendinous  septum. 

Dissection. — The  semispinalis  capitis  must  now  be  reflected  by  detaching 
it  from  the  occiput  and  throwing  it  laterally.     This  dissection  requires 


Posterior  atlanto 

occipital  membrane' 

Posterior  branch  of 

sub-occipital  nerve 

Great  occipital  nerve 

Vertebral  artery- 
Anterior  branches   / 
of  spinal  nerves'     ' 


Posterior  arch  of  atlas 
^^Ligamentum  nuchae 


Posterior  branches  of  spinal 
nerves 


Seventh  cervical  vertebra 


Fig.  72. — Dissection  of  the  Ligamentum  Nuchas  and  of  the 
Vertebral  Artery  in  the  Neck. 


care,  not  only  on  account  of  the  nerves  which  have  been  seen  to  perforate 
the  muscle  to  reach  the  surface,  but  also  on  account  of  the  structures 
which  it  covers.  In  its  upper  part  it  lies  over  the  sub-occipital  triangle 
and  the  muscles  bounding  it,  whilst  below  it  covers  the  semispinalis 
cervicis.  A  thick  dense  fascia  is  placed  over  these  subjacent  parts,  and  in 
this  lie  certain  of  the  cervical  nerves  and  the  anastomosis  between  the 
descending  branch  of  the  occipital  artery  and  the  arteria  profunda  cervicis. 
The  dissector  must  specially  look  for  a  small  twig  from  the  posterior 
branch  of  the  sub-occipital  nerve  which  enters  the  deep  surface  of  the  upper 
part  of  the  semispinalis  capitis,  and  for  a  larger  branch  to  the  same  muscle 
from  the  great  occipital  nerve. 

Ligamentum  Nuchae  (Fig.   72). — This  is  a  strong  fibrous 
partition  placed  in  the  median  plane  between  the  muscles  on 


THE  DISSECTION  OF  THE  BACK  173 

each  side  of  the  back  of  the  neck.  It  represents  a  powerful 
elastic  structure  in  quadrupeds,  which  helps  to  sustain  the  weight 
of  the  dependent  head.  In  man,  however,  there  is  not  much 
elastic  tissue  developed  in  connection  with  it,  and  it  appears 
to  be  a  continuation  upwards  of  the  supraspinous  ligament 
from  the  spine  of  the  seventh  cervical  vertebra  to  the  external 
occipital  protuberance.  In  shape  it  is  somewhat  triangular. 
By  its  base  it  is  attached  to  the  external  occipital  crest ;  by 
its  anterior  border  it  is  fixed  by  a  series  of  slips  to  the 
posterior  tubercle  of  the  atlas,  and  to  the  bifid  spines  of  the 
cervical  vertebrae,  in  the  intervals  between  their  tubercles.  Its 
apex  is  attached  to  the  spine  of  the  seventh  cervical  vertebra, 
whilst  its  posterior  border  is,  in  a  measure,  free,  and  gives 
origin  to  the  trapezius,  rhomboid,  serratus  posterior  superior, 
and  splenius  muscles. 

Arteria  Profunda  Cervicis. — The  deep  cervical  artery  springs 
from  the  costo-cervical  branch  of  the  subclavian,  and  reaches 
the  dorsum  by  passing  posteriorly  between  the  transverse 
process  of  the  last  cervical  vertebra  and  the  neck  of  the  first 
rib.  At  the  present  stage  of  the  dissection  it  is  seen  ascend- 
ing upon  the  semispinalis  cervicis  muscle  and  anastomosing 
with  the  descending  branch  of  the  occipital.  Both  vessels 
anastomose  with  twigs  from  the  vertebral  artery. 

The  arteria  profunda  cervicis  is  accompanied  by  a  large 
vein — the  vena  profunda  cervicis.  This  vessel  begins  in  the 
sub-occipital  plexus,  and  it  ends  in  the  vertebral  vein  close  to 
its  termination.  It  reaches  this  point  by  turning  forwards 
under  the  transverse  process  of  the  last  cervical  vertebra. 

Posterior  Branches  of  the  Spinal  Nerves. — The  nerves  of 
the  back  must  now  be  examined.  They  are  the  posterior 
branches  of  the  spinal  nerves.  With  four  exceptions  (viz., 
the  first  cervical,  fourth  and  fifth  sacral,  and  the  coccygeal 
nerves),  each  posterior  division  will  be  found  to  divide  into  a 
lateral  and  a  medial  division. 

Examine  these  nerves  successively  in  the  cervical,  dorsal,  and  lumbar 
regions.  It  is  well,  however,  to  defer  the  dissection  of  the  sacral  and 
coccygeal  nerves  until  the  multifidus  muscle  has  been  studied. 

Cervical  Region. — In  this  region  the  posterior  branches 
of  the  spinal  nerves  are  eight  in  number.  The  posterior 
branch  of  the  sub-occipital  or  first  nerve  fails  to  divide  into  a 
medial  and  a  lateral  division.     It  lies   deeply  in   the  sub- 


174  HEAD  AND  NECK 

occipital  triangle,  and  will  be  examined  when  this  space  is 
dissected. 

The  posterior  branch  of  the  second  cervical  nerve  is  very 
large.  It  appears  between  the  vertebral  arches  of  the  atlas 
and  epistropheus  vertebrae.  The  posterior  branches  of  the 
succeeding  six  cervical  nerves  arise  from  the  corresponding 
spinal  nerve-trunks  in  the  intervertebral  foramina.  They  turn 
dorsally  on  the  medial  sides  of  the  posterior  intertransverse 
muscles,  and  appear  in  the  intervals  between  the  transverse 
processes. 

The  lateral  divisions  are  of  small  size,  and  are  entirely 
devoted  to  the  supply  of  adjacent  muscles. 

The  medial  divisions  are  not  all  distributed  alike,  nor 
indeed  do  they  present  the  same  relations.  Those  from  the 
second^  ihird^  fourth^  and  fifth  nerves  run  medially  towards  the 
spinous  processes,  superficial  to  the  semispinalis  cervicis 
muscle,  and  under  cover  of  the  semispinalis  capitis.  When 
close  to  the  median  plane  they  turn  posteriorly,  pierce  the 
semispinalis  capitis,  splenius,  and  trapezius  muscles,  and 
become  superficial.  In  their  course  to  the  surface  they  give 
numerous  twigs  to  the  neighbouring  muscles. 

The  medial  division  of  the  second  nerve  is  remarkable  for 
its  large  size.  It  receives  the  special  name  of  great  occipital. 
It  will  be  noticed  turning  round  the  lower  border  of  the 
inferior  oblique  muscle,  to  which  it  supplies  some  twigs.  In 
passing  to  the  surface  it  pierces  the  semispinalis  capitis  (O.T. 
complexus)  and  trapezius.  To  the  former  it  gives  several 
twigs.  The  distribution  of  this  nerve  on  the  occiput  has 
been  noticed  already  (p.  156). 

The  medial  division  of  the  third  nerve  also  sends  an  offset 
to  the  occipital  portion  of  the  scalp  (p.  156). 

The  medial  divisions  of  the  lower  three  posterior  branches 
of  the  cervical  nerves  resemble  the  preceding,  in  so  far  that 
they  take  a  course  medially  towards  the  spinous  processes. 
They  differ  from  them,  however,  in  running  deep  to  the  semi- 
spinalis cervicis,  and  in  being,  as  a  rule,  entirely  expended 
in  the  supply  of  muscles. 

Dorsal  Region. — The  posterior  branches  of  the  thoracic 
nerves  make  their  appearance  in  the  intervals  between  the 
transverse  processes.  The  lateral  divisions  proceed  laterally, 
under  cover  of  the  longissimus  muscle,  and  appear  in  the 
interval  between  the  longissimus  dorsi  on  the  one  hand  and 


THE   DISSECTION  OF  THE  BACK  175 

the  ilio-costalis  on  the  other.  The  upper  six  or  seven  of  these 
nerves  are  exhausted  in  the  supply  of  the  middle  and  lateral 
columns  of  the  sacrospinalis ;  the  lower  five  or  six,  however, 
are  considerably  larger,  and  contain  both  motor  and  sensory 
fibres.  After  giving  up  their  motor  fibres  to  the  muscles, 
they  become  superficial,  by  piercing  the  serratus  posterior  in- 
ferior and  the  latissimus  dorsi,  in  a  line  with  the  angles  of 
the  ribs.  The  cutaneous  distribution  of  these  nerves  has 
already  been  examined  by  the  dissector  of  the  upper  limb. 

The  medial  divisions  also  are  distributed  differently  in  the 
upper  and  lower  portions  of  the  dorsal  region.  The  lower 
five  or  six  are  very  small,  and  end  in  the  multifidus 
muscle.  The  upper  six  or  seven  pass  medially  between  the 
multifidus  and  semispinalis,  and  after  supplying  the  muscles 
between  which  they  are  situated,  they  become  superficial.  In 
passing  towards  the  surface  they  pierce  the  splenius,  rhom- 
boids, and  trapezius  muscles,  and  thus  gain  the  superficial 
fascia,  where  they  have  been  dissected  already. 

Lumbar  Region. — The  medial  divisions  of  the  posterior 
branches  of  the  five  lumbar  nerves  are  small,  and,  like  the 
corresponding  twigs  in  the  lower  dorsal  region,  they  have 
a  purely  muscular  distribution.     They  end  in  the  multifidus. 

The  lateral  divisions  sink  into  the  substance  of  the  sacro- 
spinalis, and  are  concerned  in  the  supply  of  that  muscle,  and 
also  of  the  lumbar  intertransverse  muscles.  The  upper  three 
of  these  nerves  are  of  large  size,  and  become  cutaneous  by 
piercing  the  superficial  lamella  of  the  lumbo-dorsal  fascia. 
They  have  already  been  traced  by  the  dissector  of  the  lower 
limb  to  the  skin  of  the  gluteal  region.  The  lowest  lateral 
division  communicates  with  the  corresponding  branch  of  the 
first  sacral  nerve. 

Blood  Vessels  of  the  Back. — In  the  cervical  region  the 
dissector  has  already  noticed  the  arteria  profunda  cervicis, 
and  the  descending  branch  of  the  second  part  of  the  occipital 
artery.  Deep  in  the  sub-occipital  region  he  will  subsequently 
meet  with  a  small  portion  of  the  vertebral  artery.  In  addition 
to  these,  however,  minute  twigs  may  be  discovered,  in  a  well- 
injected  subject,  passing  posteriorly  from  the  vertebral  artery 
in  the  intervals  between  the  transverse  processes,  and  also  in 
the  sub-occipital  space.  These  supply  the  muscles,  and 
anastomose  with  the  other  arteries  in  this  region. 

In  the  dorsal  region  the  posterior  branches  of  the  aortic  inter- 


176  HEAD  AND  NECK 

costal  arteries  make  their  appearance  between  the  transverse 
processes.  Each  of  these  vessels  reaches  this  point  by 
passing  dorsally  in  the  interval  between  the  body  of  a  vertebra 
and  the  anterior  costo-transverse  ligament.  It  is  associated 
with  the  corresponding  posterior  branch  of  a  spinal  nerve, 
and  is  distributed  with  it  to  the  muscles  and  integument  of 
the  back. 

In  the  lumbar  region  similar  branches  are  derived  from  the 
lumbar  arteries.     They  are  distributed  in  the  same  manner. 

In  both  dorsal  and  lumbar  regions  these  vessels,  before 
reaching  the  back,  furnish  small  spinal  branches  which  enter 
the  vertebral  canal  through  the  intervertebral  foramina. 
These  will  be  traced  at  a  later  period. 

The  veins  accompanying  the  dorsal  branches  of  the  lumbar 
and  intercostal  arteries  pour  their  blood  into  the  lumbar 
and  intercostal  veins.  They  are  of  large  size,  being  joined 
by  tributaries  from  the  posterior  vertebral  venous  plexus,  and 
also  by  others  from  within  the  vertebral  canal. 

Dissection. — The  remains  of  the  third  layer  of  spinal  muscles  must  now 
be  dissected.     They  are  the  semispinalis  dorsi  and  semispinalis  cervicis. 

The  semispinalis  cervicis  is  already  exposed  ;  but  to  display  the 
semispinalis  dorsi  it  is  necessary  to  remove  the  spinalis  dorsi  muscle. 

The  semispinalis  dorsi  is  composed  of  a  series  of  muscular  slips,  with 
long  tendons  at  either  end,  which  arise  from  the  transverse  processes  of  the 
sixth  to  the  tenth  thoracic  vertebrae.  It  is  inserted  into  the  spines  of  the 
upper  four  thoracic  and  lower  two  cervical  vertebrae.  The  semispinalis 
cervicis  lies  under  cover  of  the  semispinalis  capitis.  It  springs  from  the 
transverse  processes  of  the  upper  five  thoracic  vertebrae,  and  is  inserted  into 
the  spines  of  the  second  to  the  fifth  cervical  vertebrae.  The  slips  composing 
the  semispinalis  muscles  stretch  over  five  or  more  vertebrae. 

Dissection. — The  fourth  layer  of  muscles  must  now  be  examined.  It 
includes  the  multifidus,  the  rotatores,  the  interspinales,  theintertransversales, 
and  the  recti  and  oblique  muscles  of  the  sub-occipital  region.  The  latter  have 
already  been  exposed  by  the  reflection  of  the  semispinalis  capitis  (complexus). 
To  display  the  other  members  of  the  group  the  semispinalis  dorsi  and 
cervicis  must  be  detached  from  the  spines  and  drawn  aside,  and  the 
sacrospinalis  must  be  separated  from  the  lumbar  and  sacral  spines  and 
turned  laterally,  if  this  has  not  already  been  done  in  tracing  the  nerves. 

Musculus  Multifidus. — In  the  lumbar  and  sacral  regions  the  multi- 
fidus will  be  seen  to  constitute  a  thick  fleshy  mass,  which  clings  closely 
to  the  vertebral  spines.  In  this  situation  it  has  a  very  extensive  origin — 
viz.,  (i)  from  the  deep  surface  of  the  aponeurotic  origin  of  the  sacrospinalis  ; 

(2)  from  the  posterior  surface  of  the  sacrum  as  low  as  the  fourth  aperture  ; 

(3)  from  the  posterior  sacro-iliac  ligament ;  (4)  from  the  posterior  superior 
spine  of  the  ilium  ;  and  (5)  from  the  mammillary  processes  of  the  lumbar 
vertebrae.  In  the  thoracic  region  it  takes  origin  from  the  transverse  processes 
of  the  vertebrae,  and  in  the  cervical  regioit  from  the  articular  processes  of  at 
least  four  of  the  lower  cervical  vertebrae.     The  bundles  which  compose  the 


THE  DISSECTION  OF  THE  BACK  177 

multifidus  pass  over  two,  three,  or  four  vertebrae,  and  are  inserted  into  the 
whole  length  of  the  various  spinous  processes  of  the  movable  vertebrae  as 
high  up  as  the  epistropheus  (O.T.  axis). 

Musculi  Rotatores. — These  are  a  series  of  small  muscles  which  may  be 
exposed  by  raising  the  multifidus.  In  the  dorsal  region  each  muscle  springs 
from  the  root  of  a  transverse  process,  and  is  inserted  into  the  lamina  of  the 
vertebra  immediately  above,  close  to  the  root  of  the  spinous  process. 
Somewhat  similar  muscles  have  been  described  in  the  cervical  and  lumbar 
regions,  and  also  a  series  of  longer  and  more  superficial  slips  which  connect 
alternate  vertebrae  with  each  other. 

Musculi  Interspinales  and  Intertransversarii.  —  The  interspinous 
Ditisdes  can  hardly  be  said  to  exist  in  the  dorsal  region,  except  in  its  upper 
and  lower  parts,  where  they  are  present  in  a  rudimentary  condition.  In 
the  neck  they  are  arranged  in  pairs,  occupying  each  interspinous  interval, 
with  the  exception  of  that  between  the  epistropheus  and  atlas.  In  the 
lumbar  region  also  they  are  well  marked  and  in  pairs  :  here  they  are 
attached  to  the  whole  length  of  the  spinous  processes.  The  inteHransverse 
muscles  are  strongly  developed  in  the  lumbar  region,  and  occupy  the  entire 
length  of  the  intertransverse  intervals.  Additional  rounded  fasciculi  may 
be  observed  passing  between  the  accessory  processes.  These  are  termed 
the  interaccessorii.  In  the  dorsal  region  intertransverse  muscles — poorly 
developed— are  found  only  in  the  lower  three  or  four  spaces.  In  the  cervical 
regiofi  they  are  present  in  pairs  and  will  be  examined  subsequently. 

Levatores  Costamm. — These  constitute  a  series  of  twelve 
fan-shaped  muscles,  which  are  classified  as  muscles  of  the  thorax, 
but  they  are  exposed  when  the  longissimus  and  ilio-costalis 
are  removed,  and  therefore  should  be  examined  now.  They 
pass  from  the  transverse  processes  to  the  ribs.  The  first 
muscle  of  the  series  springs  from  the  tip  of  the  transverse 
process  of  the  last  cervical  vertebra,  and,  expanding  as 
it  proceeds  downwards  and  laterally,  it  is  inserted  into  the 
outer  border  of  the  first  rib,  immediately  beyond  the 
tubercle.  Each  of  the  succeeding  muscles  takes  origin  from 
the  tip  of  a  thoracic  transverse  process,  and  is  inserted  into 
the  outer  surface  of  the  rib  immediately  below,  along  a  line 
extending  from  the  tubercle  to  the  angle. 

Posterior  Branches  of  the  Sacral  Nerves. — These  are 
very  small.  The  upper  four  will  be  found  emerging  from 
the  posterior  sacral  foramina ;  the  fifth  appears  at  the  lower 
end  of  the  sacral  canal. 

To  expose  the  iipper  three  the  multifidus  covering  the 
upper  three  sacral  apertures  must  be  carefully  removed. 
Each  of  these  three  nerves  will  be  found  to  divide  in 
the  usual  manner  into  a  medial  and  lateral  division. 

The  7Jiedial  divisions  are  very  fine,  and  end  in  the 
multifidus. 

The    lateral    divisions    are    somewhat    larger,     and    join 

VOL.  II — 12 


1 78  HEAD  AND  NECK 

together  so  as  to  form  a  looped  plexus  upon  the  dorsum  of  the 
sacrum.  This  communicates  above  with  the  lateral  division 
of  the  last  lumbar  nerve  and  below  with  the  posterior  branch 
of  the  fourth  sacral  nerve.  Branches  proceed  from  the  loops 
to  the  surface  of  the  sacro-tuberous  ligament  (O.T.  great  sacro- 
sciatic).  Finally  they  become  superficial  by  piercing  the 
glutseus  maximus  muscle,  and  they  supply  a  limited  area  of 
skin  over  the  glutseal  region.  They  have  already  been 
examined  by  the  dissector  of  the  lower  limb. 

The  lowest  two  posterior  branches  of  the  sacral  nerves 
do  not  separate  into  medial  and  lateral  divisions.  They 
are  very  small,  and,  after  communicating  with  each  other, 
and  also  with  the  coccygeal  nerve^  they  distribute  filaments  to 
the  parts  on  the  posterior  aspect  of  the  lower  portion  of  the 
sacrum  and  on  the  dorsal  aspect  of  the  coccyx. 

Twigs  from  the  lateral  sacral  artery  accompany  the  sacral 
nerves  and  anastomose  with  twigs  from  the  glutaeal  arteries. 

Posterior  Branch  of  the  Coccygeal  Nerve. — This  is  a 
slender  twig  which  emerges  from  the  inferior  opening  of  the 
sacral  canal,  and,  after  being  joined  by  a  filament  from  the 
last  sacral  nerve,  is  distributed  on  the  dorsum  of  the  coccyx. 

Posterior  Vertebral  Venous  Plexus. — A  plexus  of  veins  is 
situated  upon  the  superficial  aspect  of  the  vertebral  arches 
subjacent  to  the  multifidus  muscle.  This  plexus  collects 
blood  from  the  integument  and  muscles  of  the  back,  and 
in  the  thoracic  and  lumbar  regions  pours  it  into  the  posterior 
tributaries  of  the  intercostal  and  lumbar  veins.  In  the  neck 
it  is  especially  well  marked,  and  its  blood  is  emptied  into  the 
vertebral  veins.  Not  many  of  these  venous  channels  will  be 
seen  in  an  ordinary  dissection.  They  are,  however,  a  source 
of  serious  trouble  during  operations  upon  the  vertebrae. 

Dissection. — The  fourth  day  after  the  body  is  placed  upon  its  face 
must  be  devoted  to  the  dissection  of  the  sub-occipital  triangle,  and  the 
fifth  day  to  the  display  of  the  medulla  spinalis  (O.T.  spinal  cord),  its 
membranes,  nerve-roots,  and  blood  vessels. 

If  the  dissector  is  pushed  for  time,  it  is  better  that  he  should  proceed  at 
once  to  expose  the  spinal  medulla,  and  defer  the  dissection  of  the  sub- 
occipital region  until  the  head  and  neck  have  been  removed  from  the  body. 

Sub-Occipital  Space. — The  sub-occipital  space  is  a  small 
triangular  area,  exposed  by  the  reflection  of  the  semi- 
spinalis  capitis  (O.T.  complexus)  and  the  splenius  muscle. 
It    is    bounded    by    three    muscles  —  (i)    the    rectus    capitis 


THE  DISSECTION  OF  THE  BACK 


179 


posterior  major  forms  its  upper  and  medial  boundary; 
(2)  the  obliquus  inferior  limits  it  below;  and  (3)  the  obliquus 
superior  bounds  it  above  and  to  the  lateral  side.  Its 
floor  consists  of  two  structures — viz.  the  posterior  arch  of 
the  atlas  and  the  thin  posterior  atlanto-occipital  membrane. 


Occipitalis 


Sterno-mastoid 

Meningeal  branch   __ 
of  occipital  artery 

Occipital  artery  ~[ 

\ 

Splenius  capitis  — r 

Vertebral  artery 

Digastric  post,  belly 

Sterno-mastoid 

Descending  branch  of 

occipital  artery 

Levator  scapulae  — 

Splenius  cervicis  — 
Longissimus  capitis 


"    '""  Occipital  artery 


'  Great  occipital  nerve 

Trapezius 

Semispinalis  capitis 
(O.T.  complexus) 


Superior  oblique 
Great  occipital  nerve 

Rectus  cap.  post,  minor    • 

Rectus  cap.  post,  major 
Edge  of  occ.-atlantal  membr. 
Post.  br.  of  sub-occipital  nerve 
Post,  arch  of  atlas 


Spine  of  epistropheus 

—  Inferior  oblique 

—  Semispinalis  cervicis 

Trapezius 

Semispinalis  capitis 
(O.T.  complexus) 

Splenius  capitis 


Fig.  73. Dissection  of  the  Sub-occipital  Region.     Note  that  in  this  specimen 

the  occipital  artery  is  superficial  to  the  longissimus  capitis  muscle. 

It  contaifis  a  portion  of  the  vertebral  artery  and  the  posterior 
branch  of  the  sub-occipital  or  first  cervical  nerve. 

Dissection.—^Q.iox&   cleaning   the   muscles   bounding   the  triangle,  the 

posterior  branch  of  the   sub-occipital  nerve  must  be  secured.   _  This  can 

best  be  done  by  tracing  into  the  space  the  minute  twig  which  it  has  been 

seen  to  give  to  the  deep  surface  of  the  semispinalis  capitis,  or,  if  this  has 

II— 12  a 


i8o  HEAD  AND  NECK 

not  been  retained,  by  endeavouring  to  find  the  twig  which  it  gives  to  the 
rectus  capitis  posterior  major.  The  tissue  in  which  the  nerve  lies  is  very 
dense,  and  the  dissection  is  in  consequence  somewhat  difficult. 

Rectus  Capitis  Posterior  Major. — This  muscle  springs  by  a 
pointed  origin  from  the  spine  of  the  epistropheus  (O.T.  axis), 
and,  expanding  as  it  passes  upwards  and  laterally,  it  is  inserted 
into  the  occipital  bone  along  the  lateral  portion  of  the  inferior 
nuchal  line  and  the  surface  immediately  below. 

Rectus  Capitis  Posterior  Minor. — This  is  a  small  fan- 
shaped  muscle,  placed  to  the  medial  side  of,  and  overlapped 
by,  the  preceding  muscle.  It  takes  origin  from  the  tubercle 
on  the  posterior  arch  of  the  atlas,  and  is  inserted  into  the 
medial  part  of  the  inferior  nuchal  line  of  the  occipital  bone 
and  the  surface  between  this  and  the  foramen  magnum. 

Obliquus  Capitis  Inferior. — This  muscle  extends  from  the 
extremity  of  the  spine  of  the  epistropheus  to  the  posterior 
border  of  the  transverse  process  of  the  atlas.  The  great 
occipital  nerve  will  be  seen  hooking  round  its  lower  border. 

Obliquus  Capitis  Superior. — This  muscle  springs  from 
the  transverse  process  of  the  atlas,  and  is  inserted  into 
the  occipital  bone  in  the  interval  between  the  nuchal  lines, 
below  and  to  the  lateral  side  of  the  semispinalis  capitis. 

Posterior  Branch  of  the  Sub -Occipital  Nerve.  —  The 
posterior  branch  of  the  sub-occipital  nerve  does  not  divide 
into  medial  and  lateral  divisions.  It  enters  the  sub-occipital 
triangle  by  passing  dorsally,  between  the  posterior  arch  of 
the  atlas  and  the  vertebral  artery,  and  at  once  breaks  up 
into  branches  which  go  to  supply  five  muscles — viz.  the  two 
posterior  recti,  the  two  oblique  muscles,  and  the  semispinalis 
capitis.  In  addition  to  these  muscular  twigs  it  gives  a  com- 
municating^ and  sometimes  a  cutaneous  filament. 

The  communicating  branch  generally  proceeds  from  the 
nerve  to  the  obliquus  capitis  inferior,  and  joins  the  great 
occipital  nerve.  The  cutaneous  branch.,  when  present,  accom- 
panies the  occipital  artery  to  the  integument  over  the  occiput. 

Arteria  Vertebralis. — Only  the  third  portion  of  this  vessel 
lies  in  the  sub-occipital  triangle.  Emerging  from  the  foramen 
in  the  transverse  process  of  the  atlas,  it  runs  posteriorly  and 
medially  in  the  groove  upon  the  posterior  arch  of  the  same 
bone.  In  this  course  it  lies  immediately  posterior  to  the  lateral 
mass  of  the  atlas  and  above  the  sub- occipital  nerve.  It  leaves 
the  space  by  passing  anterior  to  the  thickened    lateral   ex- 


THE  DISSECTION  OF  THE  BACK  i8i 

tension  of  the  posterior  atlanto- occipital  membrane,  which 
runs  from  the  posterior  arch  of  the  atlas  to  the  posterior  lip 
of  its  articular  process  and  is  called  the  oblique  ligament 
of  the  atlas ;  then  it  pierces  the  dura  mater  and  enters  the 
vertebral  canal. 

Small  branches  proceed  from  the  vertebral  artery  in  this 
situation  to  supply  the  parts  in  its  immediate  neighbourhood, 
and  to  anastomose  with  the  descending  branch  of  the  occipital 
artery  and  the  arteria  profunda  cervicis. 

Dissection  to  open  the  Vertebral  Canal. — The  first  step  consists  in 
thoroughly  cleaning  the  laminae  and  spinous  processes  upon  both  sides. 
The  multifidus  must  be  completely  removed  from  the  dorsum  of  the 
sacrum.  At  the  same  time  the  posterior  branches  of  the  nerves  must 
be  retained,  so  that  their  continuity  with  the  various  spinal  nerve-trunks 
may  be  afterwards  established.  The  posterior  wall  of  the  vertebral  canal 
should  now  be  removed  iii  one  piece  by  sawing  through  the  laminae  on 
either  side,  and  dividing  the  ligamenta  flava,  from  the  third  cervical 
vertebra  down  to  the  lower  opening  of  the  canal  on  the  back  of  the  sacrum. 

In  making  this  dissection  the  student  must  attend  to  the  following 
points: — (i)  the  cut  should  be  directed  through  the  laminae  close  to  the 
medial  sides  of  the  articular  processes  ;  (2)  the  saw  must  be  used  in  an  oblique 
plane,  so  that  the  cut  through  the  laminee  slants  slightly  medialwards  ; 
(3)  in  cutting  through  the  cervical  laminse  the  head  and  neck  should  hang 
over  the  end  of  the  table,  and  be  flexed  as  much  as  possible,  whilst  the 
saw  is  worked  from  below  upwards  ;  (4)  in  the  case  of  the  lumbar  region, 
where,  indeed,  most  difficulty  will  be  met,  a  high  block  must  be  placed 
under  the  abdomen  of  the  subject,  whilst  the  blocks  supporting  the  chest 
and  pelvis  are  removed.  It  will  probably  be  necessary  at  this  point  to 
have  recourse  to  the  hammer  and  chisel. 

The  laminae  and  spinous  processes  which  are  thus  removed  are  connected 
with  each  other  by  the  ligamenta  flava  and  the  supraspinous  and  inter- 
spinous  ligaments.  They  should  be  laid  aside  for  the  present.  A  de- 
scription of  these  ligaments  will  be  found  on  p.  358.  When  the  specimen 
is  fresh,  however,  the  dissector  should  test  the  high  elasticity  of  the 
ligamenta  flava  by  stretching  the  specimen. 

Between  the  dura  mater  and  the  walls  of  the  canal,  the  dissector  will 
notice  a  quantity  of  loose  areolar  tissue  and  soft  fat.  The  latter  is 
especially  plentiful  in  the  sacral  region,  where  it  somewhat  resembles  the 
marrow  in  the  medullary  cavity  of  a  long  bone.  Great  numbers  of  large 
veins  and  minute  arteries  ramify  in  this  areolo-fatty  material. 

Arterise  Spinales. — In  a  well-injected  subject  a  minute 
spinal  artery  will  be  seen  entering  the  vertebral  canal  through 
each  intervertebral  foramen.  These  arteries  are  derived  from 
different  sources  in  the  different  regions  of  the  spine.  In  the 
cervical  region  they  come  from  the  vertebral  artery,  and  in 
the  thoracic  region  from  the  posterior  branches  of  the  inter- 
costal arteries ;  in  the  lumbar  region  from  the  dorsal  branches 
of  the  lumbar  arteries.     They  supply  the  spinal  medulla  and  its 

II— 12& 


i82  HEAD  AND  NECK 

meninges,  the  bones,  the  periosteum,  and  the  ligaments ;  and 
their  arrangement  is  very  much  the  same  in  each  of  the 
three  regions. 

Each  spinal  artery  may  be  looked  upon  as  giving  off  three 
main  twigs :  of  these,  one,  termed  the  pre-laniinar  branchy 
a  very  small  twig,  ramifies  upon  the  deep  surface  of  the 
vertebral  arches  and  ligamenta  flava ;  another,  the  neural 
branchy  can  be  followed  to  the  dura  mater,  which  it  pierces 
immediately  above  the  point  of  exit  of  the  corresponding 
spinal  nerve;  whilst  the  third,  t\\e  post-central  branch,  is  carried 
medially,  anterior  to  the  dura  mater,  towards  the  posterior 
surface  of  the  vertebral  bodies,  and  divides  into  an  ascending 
and  a  descending  twig.  These  anastomosewith  the  correspond- 
ing twigs  above  and  below,  and  in  this  manner  a  continuous 
series  of  minute  arterial  arcades  is  formed,  from  which 
branches  pass  medially  to  form  a  series  of  cross  anastomoses 
with  the  corresponding  vessels  of  the  opposite  side. 

In  the  cervical  region  small  branches  from  the  ascending 
cervical  artery  also  find  their  way  into  the  vertebral  canal ; 
whilst  in  the  sacral  portion  of  the  canal  the  dissector  will  find 
branches  from  the  lateral  sacral  arteries. 

Internal  Vertebral  Venous  Plexus. — This  plexus  extends 
along  the  whole  length  of  the  vertebral  canal,  and  consists 
essentially  of  four  subsidiary  longitudinal  plexuses,  two 
anterior  and  two  posterior,  which  anastomose  freely  with 
each  other. 

The  posterior  plexuses  are  united  by  many  cross  branches, 
which  run  along  the  deep  aspect  of  the  vertebral  arches  and 
ligamenta  flava.  Above,  they  communicate  with  the  occipital 
sinus,  whilst  all  the  way  down  they  are  connected  with  the 
posterior  vertebral  venous  plexus  by  wide  channels  which  pierce 
the  ligamenta  flava.  Laterally  they  send  branches  through 
the  intervertebral  foramina  to  join  the  posterior  branches  of 
the  intercostal  and  lumbar  veins. 

The  anterior  plexuses  cannot  be  dissected  whilst  the  medulla 
spinalis  (O.T.  spinal  cord)  and  its  membranes  are  in  situ,  but 
it  is  convenient  to  describe  them  at  this  stage.  Indeed,  the 
dissection  is  one  of  considerable  difficulty,  even  under  the 
most  advantageous  circumstances.  They  form  two  main 
longitudinal  venous  channels  placed  one  upon  either  side  of 
the  posterior  longitudinal  ligament  of  the  vertebral  bodies,  and 
they  are  joined  by  transverse  branches  which  cross  the  median 


THE  DISSECTION  OF  THE   BACK  183 

plane  anterior  to  that  ligament  opposite  each  vertebral  body. 
Each  transverse  vein  receives  large  tributaries  from  the  in- 
terior of  the  vertebra.  Superiorly,  each  of  the  main  longitudinal 
channels  communicates  with  the  occipital  sinus  or  the  basilar 
plexus  within  the  cranium  ;  and  each  of  the  posterior  channels 
gives  oif  a  branch  which  emerges  above  the  posterior  arch  of 
the  atlas  to  join  the  commencement  of  the  vertebral  vein. 
Opposite  the  various  intervertebral  fibro-cartilages  the  anterior 
plexus  sends  off  branches  which  run  towards  the  inter- 
vertebral foramina,  where  they  join  with  corresponding  branches 
of  the  posterior  plexus,  to  form  the  intervertebral  veins  which 
accompany  the  corresponding  spinal  nerves. 

Meninges  of  the  Medulla  Spinalis  (Fig.  74). — The  medulla 
spinalis,  like  the  brain,  with  which  it  is  continuous,  is  enveloped 
by  three  membranes  termed  me7iinges.  The  most  external 
investment  is  a  strong  fibrous  membrane  called  the  ditra 
mater-,  the  second,  in  order  from  without  inwards,  is  a  non- 
vascular tunic  termed  the  arachnoid;  whilst  the  third  and 
most  internal  is  the  pia  mater.  These  membranes  are 
directly  continuous  with  the  corresponding  investments  of 
the  brain. 

Dissection. — The  outer  surface  of  the  dura  mater  must  now  be  cleaned. 
This  is  effected  by  removing  the  loose  areolar  tissue,  soft  fat,  and  posterior 
intraspinal  veins  from  the  vertebral  canal.  It  is  necessary,  also,  to  define 
carefully  the  numerous  lateral  prolongations  which  the  membrane  gives  to 
the  spinal  nerves. 

Dura  Mater  Spinalis  (Fig.  74). — In  the  vertebral  canal  the 
dura  mater  constitutes  an  exceedingly  dense  and  tough  fibrous 
tube,  which  extends  from  the  foramen  magnum  above,  to  the 
level  of  the  second  or  third  piece  of  the  sacrum  below.  It  is 
separated  from  the  walls  of  the  vertebral  canal  and  its  lining 
periosteum  by  an  interval,  which  is  filled  by  loose  fat  and  areolar 
tissue,  and  the  internal  vertebral  venous  plexus.  Even 
before  the  membranous  tube  is  laid  open,  the  dissector  can 
readily  satisfy  himself  that  it  forms  a  very  loose  sheath  around 
the  spinal  medulla  and  the  nerve-roots  which  form  the  cauda 
equina ;  in  other  words,  it  is  very  capacious  in  comparison 
with  the  volume  of  its  contents.  Its  calibre,  moreover,  is  by 
no  means  uniform  ;  in  the  cervical  and  lumbar  regions  it  is 
considerably  wider  than  in  the  thoracic  region,  whilst  in  the 
sacral  canal  it  rapidly  contracts  and  finally  ends  by  blending 
with  the  filutn  terminale.,  a  fibrous  thread  which  is  prolonged 
II— 12  c 


i84 


HEAD  AND  NECK 


downwards  through  the  sacral  canal  from  the  extremity  of  the 
medulla  spinalis  (O.T,  spinal  cord). 

The  cylindrical  tube  of  spinal  dura  mater  does  not  lie 
free  within  the  vertebral  canal,  although  its  attachments  are 
of  such  a  nature  that  they  do  not  in  any  way  interfere  with 
the  free  movement  of  the  vertebral  column.  Above,  the  dura 
mater  is   firmly   attached  to   the   second   and   third  cervical 

Dura  mater 
Arachnoid 
Ligamentum  denticulatum 


x^rachnoid 


Posterior  nerve-root 


Spinal  gan 

Anterior  branch 
of  nerve 

Posterior  branch 
of  nerve 


Dura  mater 


Anterior  nerve-root 
(cut) 

Posterior  nerve-root 

Anterior  nerve-root 
(cut) 


Ligamentum 
denticulatum 


Pia  mater 


Anterior  nerve-root 


Fig.  74. — Membranes  of  the  Medulla  Spinalis  (O.T.  Spinal  Cord),  and  the 
mode  of  origin  of  the  Spinal  Nerves. 

vertebrae,  and  around  the  margin  of  the  foramen  magnum  ; 
below,  the  filum  terminale,  on  which  it  terminates,  can  be 
traced  as  far  as  the  dorsal  aspect  of  the  coccyx,  where  it  is 
lost  by  blending  with  the  periosteum.  On  either  side  the 
spinal  nerve-roots,  as  they  pierce  the  dura  mater,  carry  with 
them  into  the  intervertebral  foramina  tubular  sheaths  of  the 
membrane,  which  are  attached  to  the  margins  of  the  foramina, 
whilst,  anteriorly,  loose  fibrous  prolongations — more  numerous 
above  and  below  than  in  the  dorsal  region — connect  the  tube 
of  dura  mater  to   the  posterior  longitudinal  ligament  of  the 


THE  DISSECTION  OF  THE  BACK  185 

vertebral  column.      No  connection  of  any  kind  exists  between 
the  dura  mater  and  the  vertebral  arches  or  ligamenta  flava. 

Dissection. — The  tube  of  dura  mater  may  now  be  opened  with  the 
scissors.  The  incision  should  be  carried  through  the  membrane  in  the 
median  plane.  Care,  however,  must  be  taken  not  to  injure  the  delicate 
arachnoid,  which  is  subjacent. 

Cavum  Subdurale. — The  subdural  cave  (O.T.  space)  is  the 
capillary  interval  between  the  dura  mater  and  the  arachnoid 
(Fig.  74).  The  deep  surface  of  the  dura,  which  is  turned 
towards  this  space,  is  smooth,  moist,  and  polished.  The 
dissector  will  notice,  upon  either  side,  the  series  of  apertures 
of  exit  for  the  roots  of  the  spinal  nerves.  These  are  ranged 
in  pairs  opposite  each  intervertebral  foramen.  The  subdural 
space  is  prolonged  laterally,  for  a  short  distance,  upon  each 
of  the  nerve-roots,  and  has  a  free  communication  with  the 
lymph  paths  present  in  the  nerves. 

Viewed  from  the  inside  of  the  tube  of  dura  mater,  each  of  the  two 
nerve-roots  belonging  to  a  spinal  nerve  is  seen  to  carry  with  it  a  special 
and  distinct  sheath.  When  examined,  however,  on  the  outside  of  the  tube 
of  dura  mater,  they  appear  to  be  enveloped  in  one  sheath,  because  the  two 
sheaths  are  closely  held  together  on  the  outside  by  intervening  connective 
tissue,  which  can  be  removed  with  a  little  careful  dissection.  When  this  is 
done,  the  two  tubular  sheaths  will  be  seen  to  remain  distinct  as  far  as  the 
ganglion  on  the  posterior  root  of  the  nerve.  At  that  point  they  blend 
with  each  other. 

Arachnoidea  Spinalis  (Fig.  74). — The  arachnoid  resembles 
the  dura  mater  in  forming  a  loose,  wide  investment  for 
the  spinal  medulla.  Unlike  the  dura,  however,  it  is  remark- 
able for  its  great  delicacy  and  transparency.  The  sac  which 
it  forms  is  most  capacious,  and  can  be  demonstrated  most 
easily  towards  its  lower  part,  where  it  envelops  the  extremity 
of  the  spinal  medulla  and  the  collection  of  long  nerve-roots 
which  constitute  the  cauda  equitia.  Make  an  incision  into  it, 
and  insert  the  handle  of  the  scalpel,  or,  better  still,  inflate  the 
sac  with  air  by  means  of  a  blowpipe.  Above,  the  arachnoid 
becomes  continuous,  at  the  level  of  the  foramen  magnum,  with 
the  arachnoid  membrane  of  the  brain,  whilst,  laterally,  it  is 
prolonged  upon  the  various  nerve-roots,  thus  contributing 
to  each  a  tubular  sheath.  It  terminates  blindly  below  at  the 
level  of  the  second  or  third  sacral  vertebra. 

Cavum  Subaraclinoideale  (Fig.  74). — This  term  is  applied 
to  the  wide  space  between  the  arachnoid  and  pia  mater.  It 
is  occupied  by  a  variable  amount  of  cerebro-spinal  fluid,  and 


i86  HEAD  AND  NECK 

is  directly  continuous  with  the  cranial  sub-arachnoid  space. 
Three  incomplete  septa  partially  subdivide  the  spinal  sub- 
arachnoid space  into  compartments.  One  of  these  septa  is  a 
median  partition  called  the  septum  subarachnoideale,  which  con- 
nects the  pia  mater  covering  the  posterior  aspect  of  the  spinal 
medulla  with  the  arachnoid.  In  the  upper  part  of  the  cervical 
region  the  subarachnoid  septum  is  represented  merely  by  a 
number  of  strands  passing  between  the  two  membranes  ;  in  the 
lower  part  of  the  cervical  region  and  in  the  thoracic  region  it  is 
almost  complete.  The  two  other  septa  are  formed  by  the  liga- 
menta  denticulata.  These  spread  outwards  from  each  side  of 
the  medulla  spinalis,  and  will  be  studied  with  the  pia  mater. 

Dissection. — Take  away  the  arachnoid  mater  from  a  portion  of  the  spinal 
medulla,  and  proceed  to  the  study  of  the  pia  mater. 

Pia  Mater  Spinalis. — This  is  a  firm  vascular  membrane, 
closely  adherent  to  the  surface  of  the  medulla  spinalis  (O.T. 
spinal  cord).  It  is  thicker  and  denser  than  the  pia  mater 
of  the  brain,  largely  owing  to  the  addition  of  an  outer  layer 
of  fibres  which  run  chiefly  in  a  longitudinal  direction.  The 
pia  mater  sends  a  fold  into  the  antero-median  fissure  of  the 
medulla  spinalis,  and  the  septum  which  occupies  the  posterior 
median  fissure  of  the  medulla  spinalis  is  firmly  attached  to 
its  deep  surface.  Anteriorly,  in  the  median  plane,  the  pia 
mater  is  thickened  to  form  a  longitudinal  glistening  band, 
which  receives  the  name  of  the  linea  splendens.  Of  course, 
this  can  be  seen  only  after  the  medulla  spinalis  (O.T.  spinal 
cord)  has  been  removed  from  the  vertebral  canal.  The  blood 
vessels  of  the  medulla  spinalis  lie  between  the  two  layers  of  the 
pia  mater  before  they  enter  the  substance  of  the  spinal  medulla, 
and  the  various  spinal  nerves  receive  from  it  closely  fitting 
sheaths  which  blend  with  their  connective-tissue  sheaths. 

Ligamentum  Denticulatum  (Figs.  74  and  75). — This  is  a 
remarkable  band,  which  stretches  laterally  from  either  side 
of  the  medulla  spinalis,  and  connects  it  with  the  dura  mater. 
Its  pial  or  medial  attachment  extends  in  a  continuous  line, 
between  the  anterior  and  posterior  nerve-roots,  from  the  level 
of  foramen  magnum  above  to  the  level  of  the  body  of  the  first 
lumbar  vertebra  below.  Its  lateral  margin  is  widely  serrated  or 
denticulated.  From  twenty  to  twenty-two  denticulations  may 
be  recognised,  and  the  highest  is  attached  to  the  margin  of 
the  foramen  magnum.    They  occur  in  the  intervals  between  the 


THE  DISSECTION  OF  THE  BACK 


187 


Ligamentum 
denticulatum 


spinal  nerves,  and,  pushing  the  arachnoid  before  them,  they 
are  attached  by  their  pointed  extremities  to  the  inner  surface 
of  the  dura  mater. 

The  ligamenta  denticulata  maintain  the  medulla  spinalis 
(O.T.  spinal  cord)  in  the  middle  of  the  tube  of  dura  mater  and 
partially  subdivide  the  sub-arachnoid  space  into  an  anterior 
and  a  posterior  compartment.  In  the  anterior  compartment 
the  anterior  nerve-roots  pass  laterally ;  the  posterior  compart- 
ment contains  the  posterior  nerve-roots,  and  is  imperfectly 
subdivided  into  two  lateral  subdivisions  by  the  septum 
posticum. 

Medulla  Spinalis 
(O.T.  Spinal  Cord). 
— The  spinal  medulla 
itself  may  now  be 
studied  in  situ.  It  is 
a  cylindrical  structure, 
slightly  flattened  an- 
teriorly and  pos- 
teriorly, which  extends 
from  the  foramen 
magnum,  where  it  is 
continuous  with  the 
medulla  oblongata  of 
the  brain,  to  the 
lower  border  of  the 
body  of  the  first  or 
the  upper  border  of  the  body  of  the  second  lumbar  vertebra. 
Its  lower  end  rapidly  tapers  to  a  point,  and  is  termed  the 
C071US  medullaris.  From  the  extremity  of  this,  a  slender  fila- 
ment, termed  the  filimi  ter??ii?ia!e,  is  prolonged  downwards  to 
the  dorsal  surface  of  the  coccyx. 

In  the  female  the  average  length  of  the  medulla  spinalis  is 
43  cm.  j  in  the  male  it  is  45  cm. 

Throughout  the  greater  part  of  the  thoracic  region  of  the 
spine  the  medulla  spinalis  presents  a  uniform  girth,  but  in  the 
cervical  and  lower  thoracic  regions  it  shows  marked  swellings, 
termed  respectively  the  intumescentia  cervicalis  and  intiimescentia 
lu77ibalis.  From  these  enlargements  proceed  the  nerves  which 
supply  the  upper  and  lower  limbs.  The  ceiuical  sivellifig  is  the 
more  evident  of  the  two.  It  begins  at  the  upper  end  of  the 
medulla  spinalis  (O.T.  spinal  cord)   and   attains  its   greatest 


Fig.  75. — Lateral  view  of  the  ^Medulla  vSpinalis, 
Dura  Mater,  and  Ligamentum  Denticulatum. 
(Hirschfeld  and  Leveill^.) 


i88 


HEAD  AND  NECK 


L.V.I.  . 


Conus 
medullaris 


Filum 

terminale 

internum 


breadth  (13  to  14  mm.)  opposite  the  fifth  or  sixth  cervical 
vertebra.  Below,  it  subsides  opposite  the  second  thoracic 
vertebra.  The  lumbar  swelling  begins  at  the  level  of  the  tenth 
thoracic  vertebra,  and  attains  its  maximum  transverse  diameter 
(11  to  13  mm.)  opposite  the  last  thoracic  vertebra.     Below,  it 

rapidly    tapers     into    the 
conus  medullaris. 

Filum  Terminale. — 
This  delicate  thread-like 
filament  lies  amidst  the 
numerous  long  nerve-roots 
which  occupy  the  lower 
part  of  the  vertebral  canal, 
but  it  can  readily  be  de- 
tected from  these  (i)  by 
its  silvery  glistening  ap- 
pearance, and  (2)  by  its 
continuity  with  the  ex- 
tremity of  the  conus 
itiedullaris. 

Although  the  central, 
canal  of  the  medulla 
spinalis  is  prolonged 
down  in  its  interior 
for  nearly  half  its 
length,  and  nervous 
elements  can  be 
traced  in  its  sub- 
stance for  a  like 
distance,  the  filum 
terminale  is  chiefly 
composed  of  pia 
mater.  The  linea 
splendens  and  the 
lower   ends   of   the 


S.V.I. 


Lower  end 
of  tube  of 
dura  mater 


-Coccyx 


Fig.  76. — Sagittal  section  through  the  lower  part 
of  the  Vertebral  Canal. 


ligamefita  denticulata  may  also  be  considered  to  be  continued 
into  it.  At  the  level  of  the  second  or  third  sacral  vertebra 
it  pierces  the  tapered  end  of  the  tube  of  dura  mater,  and 
receives  an  investment  from  it ;  and,  finally,  reaching  the  lower 
end  of  the  sacral  canal,  it  terminates  by  blending  with  the 
periosteum  on  the  dorsal  surface  of  the  coccyx  or  the  last 
piece  of  the  sacrum. 


THE  DISSECTION  OF  THE  BACK  189 

In  length  it  measures  about  six  inches.  The  part  within 
the  tube  of  dura  is  termed  the  filum  terminale  internmfi,  the 
portion  outside  is  th.Q  filum  ter?7ii?iale  externum. 

Spinal  Nerves. — Thirty-one  spinal  nerves  take  origin  from 
each  side  of  the  medulla  spinalis  (O.T.  spinal  cord).  These 
are  classified  into  five  groups,  according  to  the  vertebrae  with 
which  they  are  associated.  The  thoracic,  lumbar,  and  sacral 
nerves  correspond  in  number  with  the  vertebrae  in  each  of 
those  regions — thus,  there  are  twelve  thoracic,  five  lumbar, 
and  five  sacral  nerves,  each  of  which  issues  from  the  vertebral 
canal  below  the  vertebra  with  which  it  numerically  corresponds. 
In  the  cervical  region,  however,  there  are  eight  nerves,  the 
first  of  which  comes  out  between  the  occiput  and  the  atlas, 
and  is  therefore  distinguished  by  the  special  name  of  the  sub- 
occipital nerve.  There  is  only  one  coccygeal  nerve  on  each 
side. 

Spinal  Nerve-Roots  (Figs.  75  and  77). — Each  spinal  nerve 
springs  from  the  side  of  the  spinal  medulla  by  two  roots — an 
anterior  a-ud  sl posterior.  Except  in  the  case  of  the  sub-occipital 
nerve  (where  the  posterior  root  is  sometimes  absent),  the 
posterior  nerve-root  is  the  larger  of  the  two.  In  addition, 
the  posterior  root  is  distinguished  by  possessing  an  oval 
ganglion,  termed  the  spinal  ganglion.  There  is,  also,  a 
wide  physiological  difference  between  the  two  roots — the 
posterior  root  is  composed  of  afferent  fibres,  the  anterior  root 
consists  of  efferent  fibres.  Immediately  beyond  the  ganglion 
the  two  roots  unite  to  form  the  spi7ial  7ierve-trunk,  which 
contains  a  mixture  of  both  efferent  and  afferent  nerve-fibres. 

The  mode  of  attachment  of  the  two  nerve-roots  to  the  side  of 
the  medulla  spinalis  is  somewhat  different  in  the  two  cases. 
In  each  instance  they  are  attached  by  several  separate  fila 
radicularia,  which  spread  out  from  each  other  as  they  approach 
their  attachments.  In  the  case  of  the  posterior  root  the 
fila  enter  the  spinal  medulla  consecutively  along  a  continuous 
straight  line  and  at  the  bottom  of  a  slight  furrow.  The  fila 
of  the  anterior  root,  on  the  other  hand,  are  not  so  regularly 
placed.  They  emerge  from  the  medulla  spinalis  over  an  area 
of  some  breadth.  The  portion  of  the  medulla  spinalis  which 
stands  in  connection  with  a  pair  of  nerves  receives  the 
name  of  a  "neural  segment." 

It  will  be  noted  that  the  size  of  the  nerve-roots  differs  greatly. 
The  lower  lumbar   and   upper  sacral   nerve-roots   are  much 


190 


HEAD  AND  NECK 


the  larger,  whilst  the  lower  sacral  and  the  coccygeal  roots 
are  the  smaller.  In  the  cervical  region  the  roots  increase  in 
size  from  above  downwards,  but  more  rapidly  in  the  lower 
members  of  the  group  ;  in  the  thoracic  region  the  roots  of  the 
first  nerve  are  large,  but  those  which  succeed  it  are  small  and 
of  uniform  size. 

In  relative  lengthy  and  in  the  direction  which  they  follow  in 
the  vertebral  canal,  the  nerve-roots  also  show  great  differences. 
This  is  due  to  the  medulla  spinalis  being  so  much  shorter  than 
the  canal  in  which  it  lies.  In  the  upper  part  of  the  cervical 
region  the  nerve-roots  are  short,  and  proceed  laterally  in  a 
more  or  less  horizontal  direction.     Below  the  upper  cervical 


Fig.  'jj. — A  segment  of  the  medulla  spinalis  ;  anterior  aspect. 
(Schwalbe,  after  Allen  Thomson. ) 


1.  Anterior  median  fissure. 

2.  Posterior  median  sulcus. 

3  and  5.   Fila  of  anterior  nerve-root. 
4.  Posterior  lateral  groove. 


6.  Posterior  nerve-root. 
6'.  Spinal  ganglion, 

7.  Anterior  branch. 
7'.  Posterior  branch. 


region  the  nerve-roots  become  more  oblique,  and  the  lower 
the  origin  of  the  nerve  the  longer  is  its  course  in  the  canal. 
The  arrangement  of  the  lower  thoracic,  the  lumbar,  sacral,  and 
coccygeal  nerve-roots  is  particularly  characteristic.  They  are 
exceedingly  long,  and  descend  vertically  from  the  lower 
portion  of  the  medulla  spinalis,  forming  a  bundle  which  is 
called  the  cauda  equina. 

Mode  of  Exit  of  Spinal  Nerves  from  Vertebral  Canal. — 
The  lower  six  cervical  nerves,  the  thoracic  nerves,  and  the 
lumbar  nerves  make  their  exit  through  the  intervertebral 
foramina ;  whilst  each  of  the  two  branches  of  the  upper  four 
sacral  nerves  finds  its  way  out  by  a  sacral  foramen.  The 
upper  two  cervical  nerves,  the  fifth  sacral  nerve,  and  the 
coccygeal  nerve,  however,  follow  a  different  course.  The 
sub-occipital  emerges  by  passing  over  the  posterior    arch  of 


THE  DISSECTION  OF  THE  BACK 


191 


the  atlas,  and  the  second  cervical  nerve  by  passing  over  the 
vertebral  arch  of  the  epistropheus  (O.T.  axis).  The  fifth 
sacral  and  the  coccygeal  nerve  leave  the  sacral  canal  through 
its  lower  aperture  (Fig.  78). 

Dissection.  —  The   nerve-roots  of  one   or   two   spinal    nerves   in   each 
region  should  be  followed  into  the  corresponding  intervertebral  foramina. 

Filum  terminale 
\^ — -Cauda  equina 

Dura  mater 


Filum 
terminale 
Fifth  sacral  nerve 


Coccygeal  nerve 


Fig.  78. — The  Sacral  Nerve-roots  (lower  part  of  Cauda  Equina)  and  the 
Membranes  in  relation  to  them.  (After  Testut. )  The  posterior  wall  of 
Sacral  Canal  is  removed. 

This  can  be  easily  done  by  snipping  away  the  articular  processes  with  the 
bone-forceps.  The  position  of  the  ganglion  on  the  posterior  root,  the 
connections  of  the  sheath  of  dura  mater,  the  union  of  the  two  roots  to  form 
the  spinal  nerve-trunk,  and  the  division  of  the  latter  into  the  anterior 
and  posterior  branches  can  thus  be  studied.  An  attempt  should  also 
be  made  at  the  same  time  to  discover  the  minute  ramus  meningetis. 
This  is  a  fine  twig  which  is  formed  by  the  union  of  a  small  filament  from 
the  spinal  nerve-trunk  with  a  minute  branch  from  the  sympathetic  trunk. 


192  HEAD  AND  NECK 

It  takes  a  recurrent  course  through  the  intervertebral  foramen  to  end  in 
the  bones  and  periosteum  of  the  vertebral  canal. 

Ganglia  Spinalia. — These  ganglia  are  oval  swellings  de- 
veloped upon  the  posterior  nerve-roots,  just  before  they  unite 
with  the  anterior  roots  to  form  the  spinal  nerve-trunks.  They 
are  found  upon  the  posterior  roots  of  all  the  nerves,  except, 
occasionally,  upon  those  of  the  sub-occipital  and  the  coccygeal 
nerves. 

The  spinal  ganglia  are  formed  upon  the  posterior  nerve- 
roots  as  they  lie  in  the  intervertebral  foramina,  except  in  the 
cases  of  the  first  two  cervical  and  the  sacral  and  coccygeal 
nerves.  The  ganglia  of  the  first  two  cervical  nerves  lie  upon 
the  posterior  arch  of  the  first  and  the  vertebral  arch  of  the 
second  cervical  vertebrae  respectively ;  the  ganglia  of  the 
sacral  nerves  are  placed  within  the  sacral  canal,  but  out- 
side the  tube  of  dura  mater.  The  ganglion  on  the  posterior 
root  of  the  coccygeal  nerve  is  inside  the  tube  of  dura  mater. 

Spinal  Nerve -Trunks. — These  are  formed  by  the  union 
of  the  anterior  and  posterior  nerve-roots  immediately  beyond 
the  spinal  ganglia.  This  union  takes  place  in  the  case  of  the 
coccygeal  and  sacral  nerves  in  the  sacral  canal;  in  the 
lumbar,  thoracic,  and  lower  six  cervical  nerves,  in  the  inter- 
vertebral foramina ;  and  in  the  case  of  the  first  two  cervical 
nerves,  on  the  arches  of  the  atlas  and  epistropheus. 

The  nerve-trunk  is  exceedingly  short ;  indeed,  it  divides 
almost  immediately  into  its  anterior  and  posterior  branches.  In 
the  case  of  the  sacral  and  coccygeal  nerves,  this  subdivision 
takes  place  in  the  sacral  canal,  and  the  spinal  nerve-trunks 
of  these  nerves  are  distinctly  longer  than  in  the  case  of  the 
nerves  which  occupy  a  higher  level. 

The  distribution  of  the  posterior  branches  has  already 
been  examined  (p.  173). 

Dissectioti. — At  this  stage  the  dissector  may  adopt  one  of  two  methods 
in  the  further  treatment  of  the  medulla  spinalis  and  the  nerves  which  spring 
from  it.  If  the  medulla  spinalis  is  fresh  and  in  such  a  condition  that  it  may  be 
successfully  hardened,  it  is  best  to  transfer  it  at  once  to  the  preservative  fluid. 
If,  on  the  other  hand,  it  is  soft  and  not  fit  for  proper  preservation,  it  should 
be  removed  with  all  its  membranes  and  nerve-roots,  and  placed  in  a  cork- 
lined  tray  filled  with  water.  There  is  no  method  by  which  the  arachnoid, 
the  pia  mater,  the  ligamenta  denticulata,  and  the  nerve-roots  can  be  so 
well  studied  as  this. 

In  removing  the  medulla  spinalis,  the  spinal  nerves  should  be  divided  as 
they  lie  in  the  intervertebral  foramina,  and  in  such  a  manner  that  as 
long   a  piece  as  possible  of  each   nerve  remains   attached   to   the   dura 


THE  DISSECTION   OF  THE  BACK  193 

mater  and  the  spinal  medulla.  Wherever  it  is  possible  the  ganglia  should 
be  taken  with  the  nerves.  The  same  rule  applies  to  the  sacral  nerves  also. 
The  medulla  spinalis  and  its  membranes  should  then  be  cut  across  at  the 
highest  limit  of  the  vertebral  dissection.  By  pulling  upon  the  dura  mater 
the  whole  specimen  may  now  be  lifted  from  the  vertebral  canal  and  trans- 
ferred to  the  water-bath.  The  dura  mater  should  then  be  slit  down 
the  median  plane,  and  the  edges  of  the  incision  must  be  turned  aside. 
By  fixing  the  dura  mater  with  pins  to  the  cork  at  the  bottom  of  the  tray, 
the  further  dissection  can  be  conducted  with  great  advantage. 

Arteries  of  the  Medulla  Spinalis  (O.T.  Spinal  Cord). — It 

is  only  when  the  arterial  injection  is  particularly  good  that 
the  spinal  arteries  can  be  made  out  satisfactorily. 

A  large  number  of  small  arteries  are  supplied  to  the 
medulla  spinalis.  These  are  the  anterior  and  posterior  spinal 
arteries  which  spring  from  the  vertebral  in  the  cranium,  and 
a  series  of  lateral  spinal  arteries  which  reach  the  side  of  the 
medulla  spinalis  and  are  derived  from  different  sources  in 
each  region.  In  the  neck  they  come  from  the  vertebral, 
ascending  cervical,  and  deep  cervical  arteries ;  and  in  the 
thoracic  and  lumbar  regions  from  the  posterior  branches  of 
the  intercostal  and  lumbar  arteries.  By  the  anastomoses  of 
these  arterial  twigs,  five  longitudinal  trunks  are  formed  upon 
the  surface  of  the  medulla  spinalis.  One  of  these  lies  in 
the  median  plane  anteriorly,  and  may  be  termed  the  ajitero- 
viedian  artery.  The  other  four  are  placed  in  relation  to  the 
sulci  along  v/hich  the  posterior  nerve-roots  enter  the  medulla 
spinalis.  One  runs  downwards  anterior  to  the  line  of  entrance 
of  these  roots,  and  the  other  posterior  to  it  on  each  side  of 
the  medulla  spinahs.  These  slender  arterial  trunks  may  there- 
fore be  termed  the  postero-lateral  longitudinal  vessels. 

The  antero-inedian  vessel  is  formed  above  by  the  union  of  the  two 
anterior  spinal  branches  of  the  vertebral  arteries.  One  of  these  is  larger 
than  the  other,  and  takes  a  much  greater  share  in  the  formation  of  the 
median  trunk.  Below  the  level  of  the  fifth  pair  of  cervical  nerves  the 
continuity  of  the  median  vessel  depends  upon  the  reinforcements  which 
it  obtains  from  the  lateral  spinal  vessels.  The  number  of  lateral  spinal 
arteries  which  join  the  median  vessel  is  very  variable.  The  majority 
of  these  arteries  end  on  the  nerve-roots  ;  only  five  to  ten  reach  the  median 
vessel.  The  ant ei-o- median  artery  runs  downwards,  under  cover  of  the 
linea  splendens  of  the  pia  mater.  Its  calibre  is  uniform  throughout, 
and  where  the  medulla  spinalis  ends  it  proceeds  onwards  for  some  distance 
upon  the  filum  terminale. 

T\\^ postero-lateral  arteries  on  each  side  of  the  medulla  spinalis  are  formed 
in  the  upper  part  of  the  cervical  region  by  the  bifurcation  of  the  corre- 
sponding posterior  spinal  branch  of  the  vertebral  artery.  Lower  down 
their  continuity  is  maintained  by  twigs  which  reach  them  on  the  posterior 
roots  of  the  spinal  nerves  from  the  lateral  spinal  arteries.  It  may  be 
VOL.  II — 13 


194 


HEAD  AND  NECK 


regarded  as  a  rule,  that  where  a  lateral  spinal  artery  gives  a  branch  to 
one  of  the  postero-lateral  arterial  trunks,  it  does  not  furnish  another 
to  the  antero-niedian  arterial  trunk.  In  this  way  different  lateral  spinal 
arteries  are  in  connection  with  the  longitudinal  trunks  on  the  anterior 
and  posterior  aspects  of  the  medulla  spinalis.  The  postero-lateral  vessels 
end  at  the  lower  extremity  of  the  medulla  spinalis. 

From  the  five  main  arterial  channels  which  thus  extend  along  the  spinal 
medulla  numerous  anastomosing  twigs  ramify  in  the  pia  mater. 

Veins  of  the  Medulla  Spinalis. — These  veins  are  small  and 
numerous,  and  their  disposition  cannot  be  said  to  correspond 
with  that  of  the  arteries.  They  are  very  tortuous,  and  form 
a  plexus  with  elongated  meshes.  Six  more  or  less  perfect 
longitudinal  venous  trunks  may  be  noticed  on  the  surface  of 
the  medulla  spinalis  in  connection  with  this  plexus ;  two  of 
these  are  median,  and  are  placed  respectively  on  the  anterior 
and  posterior  aspects.  The  anterior  trunk  runs  upwards 
under  cover  of  the  antero-median  spinal  artery.  The  other 
four  are  lateral,  and  are  situated  two  on  either  side,  in 
relation,  respectively,  to  the  anterior  and  posterior  nerve-roots. 

Upon  each  side,  the  veins  of  the  medulla  spinahs  effect 
communications  with  the  veins  in  the  vertebral  canal  by  means 
of  small  twigs  which  run  laterally  on  the  nerve-roots. 


How  to  distinguish  tJie  anterior  from  the  posterior  surface  of 
the  medulla  spinalis. 


Anterior  Surface. 

1.  Linea  splendens. 

2.  Single  anterior  spinal   artery  in 

median  plane. 

3.  Anterior     nerve  -  roots     smaller 

than  posterior,  and  springing 
by  fila  which  emerge  from 
the  medulla  spinalis,  not  in  a 
continuous  straight  line,  but 
irregularly  over  an  area  of  some 
width. 


Posterior  Surface. 

1.  The   postero-lateral    arteries   in 

relation  to  the  posterior  nerve- 
roots. 

2.  Fila     of     origin     of     posterior 

nerve-roots  entering  themedulla 
spinalis  along  a  straight  and 
continuous  line,  and  at  the 
bottom  of  a  distinct  sulcus. 

3.  Posterior  nerve-roots  larger  than 

the  anterior,  and  provided  with 
ganglia. 


Preservation  of  the  Aleihtlla  Spinalis. — If  the  medulla  spinalis  is  in  a 
fit  state  for  preservation,  it  should  be  immersed  for  a  few  weeks  in 
methylated  spirit,  to  which  a  small  amount  (4  per  cent)  of  formalin  has  been 
added.  When  sufficiently  firm,  the  dissector  should  endeavour  to  learn 
something  of  its  internal  structure  by  making  transverse  sections  across 
it  at  different  levels,  and  inspecting  the  cut  surface  closely  with  the  naked 
eye,  or  with  the  aid  of  a  magnifying  glass. 

Internal  Structure  of  the  Medulla  Spinalis. — A  good  deal 
can  be  learned  by  a  naked-eye  inspection  of  cross  sections  of 


THE  DISSECTION  OF  THE  BACK 


195 


the  medulla  spinalis  made  in  different  regions  and  at  different 
levels. 

In  such  sections  the  antero-r?iedia?i  fissure  and  the  postero- 
median septiDH  and  sulcus^  which  partially  divide  it  along  the 
whole  of  its  length  into  right  and  left  halves,  become  obvious. 

The  antero-median  fissure  is  much  shorter  than  the  postero- 
median septum.  It  dips  dorsally  to  a  commissure  of  white 
matter,  anterior  white  conwiisstire,  which  connects  the  two 
halves  of  the  medulla  spinalis ;  and  it  contains  a  fold  of  pia 
mater  and  branches  of  the  anterior  spinal  vessels.  The 
postero-median  sulcus  is  a  shallow  furrow  which  runs  along 


Fasciculus  gracilis 


Posterior  funiculus 


Fasciculus  cuneatus 


Formatio  reticularis 

Lateral  funiculus 

Central  canal 

Root  of  accessory 

nerve 

Anterior  column  of 

grey  matter 


Entering  fila  of 
posterior  nerve-root 

Posterior  column  of 
grey  matter 


Root  of  accessor^' 
nerve 


Fila  of  anterior 
nerve-root 


Anterior  funiculus 

Fig.  79. — Transverse  section  through  the  upper  part  of  the 
Cervical  Region  of  the  Medulla  Spinalis. 


the  posterior  surface  of  the  medulla  spinalis  in  the  median 
plane,  and  the  postero-median  septum  extends  from  the 
bottom  of  the  sulcus  to  a  transverse  grey  commissure  called 
the  posterior  commissure. 

The  two  halves  of  the  medulla  spinalis,  thus  marked  off 
from  each  other,  are  to  all  intents  and  purposes  symmetrical, 
and  they  are  joined  by  a  more  or  less  broad  band  or  com- 
missure which  intervenes  between  the  anterior  fissure  and  the 
posterior  septum. 

An  inspection  of  the  surface  of  each  lateral  half  of  the 

medulla  spinalis  brings  into  view  a  groove  or  furrow  at  some 

little   distance  from  the  postero-median  sulcus ;    it  is  called 

the  poster o-lateral  sulcus 

II— 13  a 


Along  the  bottom  of  this  groove 


196  HEAD  AND  NECK 

the  fila  of  the  posterior  nerve-roots  enter  the  medulla  spinalis 
(O.T.  spinal  cord)  in  accurate  linear  order.  There  is  no 
corresponding  furrow  on  the  anterior  part  of  each  lateral  half 
of  the  medulla  spinalis  in  connection  with  the  emergence  of 
the  fila  of  the  anterior  nerve -roots ;  and  it  should  be  noted 
that  these  fila  emerge  over  a  broad  area,  which  corresponds 
in  its  width  to  the  thickness  of  the  subjacent  anterior  column 
of  grey  matter. 

The  medulla  spinalis  is  composed  of  an  inside  core  of  grey 
matter  which  is  surrounded  on  all  sides  by  an  external  coating 
of  white  matter. 

Grey  Matter  of  the  Medulla  Spinalis. — The  grey  matter  in 
the  interior  of  the  medulla  spinalis  has  the  form  of  a  fluted 
column.  When  seen  in  transverse  section,  it  presents  the 
shape  of  the  letter  H.  In  each  lateral  half  of  the  medulla 
spinalis  there  is  a  comma-shaped  mass  of  grey  matter,  the 
concavity  of  which  is  directed  laterally.  The  crescents  of 
opposite  sides  are  connected  across  the  median  plane  by  a 
transverse  band,  which  is  called  the  ^rey  commissure.  The 
postero-median  septum  passes  from  the  surface  of  the  medulla 
spinalis  to  the  grey  commissure.  The  bottom 'of  the  antero- 
median fissure  is  separated  from  it  by  an  intervening  strip 
of  white  matter  which  is  termed  the  anterior  white  commissure. 
In  the  grey  commissure  may  be  seen  the  central  canal  of 
the  spinal  medulla.  It  is  just  visible  to  the  naked  eye  as  a 
minute  speck.  This  canal  tunnels  the  entire  length  of  the 
spinal  medulla,  and  opens  above  (after  having  traversed  the 
lower  half  of  the  medulla  oblongata)  into  the  fourth  ventricle 
of  the  brain.  The  portion  of  the  grey  commissure  which  lies 
posterior  to  the  central  canal  is  called  \k\.Q  posterior  commissure^ 
the  portion  anterior  to  it  receives  the  name  of  anterior  grey 
commissure. 

In  each  crescentic  mass  of  grey  matter  certain  well-defined 
parts  may  be  recognised.  The  projecting  portions  which 
extend  posterior  and  anterior  to  the  connecting  transverse  grey 
commissure  are  termed  the  posterior  and  the  anterior  grey 
columns.  They  can  be  distinguished  from  each  other  at  a 
glance. 

The  anterior  grey  column  is  short,  thick,  and  very  blunt  at  its 
extremity.  Further,  its  extremity  is  separated  from  the  surface 
by  a  tolerably  thick  coating  of  white  matter,  through  which 
the  fila  of  the  anterior  nerve-roots  pass  on  their  way  to  the 


THE  DISSECTION  OF  THE  BACK  197 

surface.  The  thickened  end  of  the  anterior  column  is  termed 
the  caput  colunmce  anterioris,  and  the  constricted  part  close  to 
the  grey  commissure  is  called  the  cervix  coliwmm  anterioris. 
The  posterior  grey  column  in  most  localities  is  elongated  and 
narrow.  Further,  it  is  drawn  out  to  a  fine  point,  which  almost 
reaches  the  bottom  of  the  postero- lateral  sulcus.  This 
pointed  extremity  receives  the  name  of  the  apex  cohwince 
posterioris ;  the  slightly  swollen  part  which  succeeds  it  is 
the  caput  colum?tae  posterioris ;  whilst  the  slightly  constricted 
part  adjoining  the  grey  commissure  goes  under  the  name  of 
the  cervix  colu?nnce  posterioris. 

Covering  the  tip  of  the  posterior  column  there  is  a  substance 
which  differs  in  its  composition  from  the  general  mass  of  grey 
matter,  and  presents  a  translucent  appearance.  It  is  termed 
the  substantia  gelatinosa  (Rolandi). 

The  grey  matter  is  not  present  in  equal  quantity  through- 
out the  entire  length  of  the  medulla  spinalis.  Therefore  it  is 
necessary  that  it  should  be  considered  in  different  regions,  and 
it  must  be  understood,  when  the  terms  cervical,  lumbar,  sacral, 
etc.,  are  applied  to  different  portions  of  the  spinal  medulla, 
that  these  terms  apply  to  the  regions  to  which  the  nerves  of 
the  same  name  are  attached. 

Wherever  there  is  an  increase  in  the  size  of  the  nerves 
attached  to  a  particular  part  of  the  medulla  spinalis,  there  a 
corresponding  increase  of  the  grey  matter  may  be  noticed.  It 
follows  from  this  that  the  districts  in  which  the  grey  matter 
bulks  most  largely  are  the  lumbar  and  cervical  swellings. 
The  great  nerves  which  go  to  form  the  limb  plexuses  enter 
and  pass  out  from  those  portions  of  the  medulla  spinalis.  In 
the  intermediate  thoracic  region  there  is  a  reduction  in  the 
quantity  of  grey  matter,  in  correspondence  with  the  smaller 
size  of  the  thoracic  nerves. 

The  shape  of  the  crescentic  masses  of  grey  matter  is  not 
the  same  in  all  regions.  In  the  thoracic  region  both  columns 
are  narrow,  although  the  distinction  between  the  anterior  grey 
column  and  the  more  attenuated  posterior  grey  column  is  still 
sufficiently  manifest.  In  the  cervical  region  the  contrast 
between  the  grey  columns  is  most  marked ;  the  anterior  grey 
column  is  very  thick  in  comparison  with  the  posterior  grey 
column.  In  the  lumbar  region,  on  the  other  hand,  the 
difference  in  the  thickness  of  the  two  grey  columns  is  not 
nearly  so  apparent,  owing  to  a  broadening  out  of  the 
11—13  h 


198 


HEAD  AND  NECK 


Postero-median  septum 

Intermed.  post,  septum 
Fasciculus  gracilis 

Fasciculus  cuneatus 
Substantia  gela- 
tinosa  Rolandi 
Lateral  funiculus 


Central  canal 

Anterior  column 
Grey  commissure 
Antero-median  fissure 
ila  of  anterior 
nerve-root 
Anterior  funiculus 

Postero-median 
septum 

Substantia  Rolandi 
Dorsal  nucleus(0.  T. 
posterioi  vesicular 
column) 

Lateral  column 

Anterior  column 

Antero-median  fissure 


—  Postero-median  septum 
-Entering  fila  of 
posterior  nerve-root 

Dorsal  nucleus 
(O.T.  posterior 
vesicular  column) 
Lateral  column 

Antero-median 
fissure 


Postero-median 
septum 


Antero-median 
fissure 


Fig.  80. — Transverse  sections  through  the  Medulla 
Spinahs  in  different  regions.  A.  Cervical  Region  ; 
B.  Mid  -  thoracic  Region ;  C.  Lovi^er  Thoracic 
Region  ;   D.  Lumbar  Region. 


posterior  grey 
column.  A  sec- 
tion taken  from 
the  centre  of  each 
region  can  very 
readily  be  recog- 
nised  by  the 
features  men- 
tioned. 

In  the  thoracic 
region  of  the  spinal 
medulla,  more 
especially  in  the 
upper  part,  there 
is  another  char- 
acter which  is  very 
distinctive.  A 
pointed  andpromi- 
nent  triangular 
projection  juts  out 
from  the  lateral 
aspect  of  the  cres- 
centic  mass  of 
grey  matter  nearly 
opposite  the  grey 
commissure.  This 
is  called  the  lateral 
grey  column  (Fig. 
80,  B  and  C). 
It  disappears  in 
the  cervical  and 
lumbar  swellings, 
but  again  becomes 
evident  both  in 
the  upper  cervical 
and  in  the  lower 
sacral  regions. 

Below  the 
thoracic  region 
the  postero-med- 
ian septum  dimin- 


ishes and  the  antero-median  fissure  increases  in  depth,  until, 


THE  DISSECTION   OF  THE  BACK 


LV 


199 


in  the  sacral  region,  they  are  almost  equal  in  depth  and  the 
central  canal  occupies  the  centre  of  the  medulla  spinalis. 

White  Matter  of  the  Medulla  Spinalis. — The  white  matter 
forms  a  thick  coating  on  the  outside  of  the  fluted  column  of 
grey  matter.  It  is  marked  off  into  three  funiculi.  The 
posterior  fu7iiculus  is  wedge-shaped  in  transverse  section,  and 
lies  between  the  postero-median  septum  and  the  posterior 
grey  column.  The  lateral  funiculus  occupies  the  concavity  of 
the  grey  crescent.  Posteriorly  it  is  bounded  by  the  posterior 
grey  column  and  the  postero-lateral  sulcus,  whilst  anteriorly  it 
extends  as  far  as  the  most  lateral  fila  of  the  anterior  nerve- 
roots.       The    anterior  funiculus    includes    the    white    matter 


Postero-median  septum 
Postero-lateral  sulcus 


Fasciculus  cerebro-_ 
spinalis  lateralis 


Fasciculus  cerebro- 


spinalis  anterior       ^^^ 


r-i'-ciculus  gracilis 
f  asciculus  cuneatus 

_    Substantia  gelatinosa 
Rolandi 


Fasciculus  cerebello- 
\       spinalis 


Fila  of  origin  of 
the  accessory  nerve 


ntero-median  fissure 


Fig.  81. — Transverse  section  through  the  upper  cervical  part  of  the  Medulla 
Spinalis  of  a  full-time  Foetus,  treated  by  the  Pal-Weigert  process. 

between  the  antero-median  fissure  and  the  anterior  column 
of  grey  matter,  and  also  the  white  matter  which  separates 
the  thick  extremity  of  the  anterior  grey  column  from  the 
surface  of  the  spinal  medulla  and  is  traversed  by  the  emerging 
fila  of  the  anterior  nerve-roots. 

In  the  cervical  region  a  faint  longitudinal  groove  runs 
downwards  on  the  surface  of  the  posterior  funiculus  of  the 
medulla  spinalis.  This  indicates  the  position  of  a  septum 
which  passes  into  the  funiculus  from  the  deep  surface  of  the 
pia  mater  and  divides  it  incompletely  into  two  unequal  strands. 
The  groove  is  termed  the  intermediate  posterior  sulcus.  The 
strand  on  its  medial  side  is  the  fasciculus  gracilis  (Goll's), 
whilst  the  lateral  and  larger  strand  receives  the  name  of  the 
fasciculus  cuneatus  (Burdach's). 

II— 13  c 


200  HEAD  AND  NECK 

The  white  matter  of  the  medulla  spinalis  increases  steadily 
in  quantity  from  below  upwards. 

The  fasciculi  gracilis  and  cuneatus,  which  form  the  posterior  funiculus 
of  the  medulla  spinalis,  are  composed  of  fibres  which  enter  the  spinal  medulla 
as  the  fila  of  the  posterior  nerve-roots.  In  the  lower  portion  of  the  medulla 
spinalis  the  two  fasciculi  are  not  marked  off  from  each  other. 

In  the  lateral  and  anterior  funiculi  of  the  adult  spinal  medulla  it  is  not 
possible  with  the  naked  eye  to  distinguish  the  different  strands  of  fibres,  of 
which  they  consist,  but  the  student  should  remember  that  such  strands  or 
tracts  are  present.  The  three  best-defined  tracts  in  the  antero-lateral  part 
of  the  spinal  medulla  are,  (i)  the  fasciculus  cerebello-spinalis  (O.T.  direct 
cerebellar  tract)  ;  (2)  the  fasciculus  cerebro-spinalis  lateralis  (O.T.  crossed 
pyramidal  tract) ;  (3)  the  fasciculus  cerebro-spinalis  anterior  (O.T.  direct 
pyramidal  tract). 

The  fasciculus  cerebello-spinalis  ascends  to  the  cerebellum,  but,  traced 
in  the  opposite  direction,  it  is  found  to  disappear  in  the  lower  thoracic  region 
of  the  medulla  spinalis.  The  fascicuhts  cerebro-spinalis  lateralis  occupies 
a  larger  district  of  the  medulla  spinalis.  It  is  placed  in  the  lateral  funiculus 
anterior  to  the  posterior  column  of  grey  matter  and  immediately  medial  to  the 
fasciculus  cerebello-spinalis.  As  the  fasciculus  cerebello-spinalis  disappears  in 
the  lower  part  of  the  medulla  spinalis  the  fasciculus  cerebro-spinalis  lateralis 
comes  to  the  surface,  and  it  can  be  traced  as  low  as  the  fourth  sacral  nerve. 
T\i&  fasciculus  cerebro-spinalis  anterior  {ovms  the  narrow  strip  of  the  anterior 
funiculus,  which  lies  immediately  adjacent  to  the  antero-median  fissure.  It 
reaches  down  to  about  the  middle  of  the  thoracic  region  of  the  medulla 
spinalis  and  then  disappears. 

After  the  body  has  been  five  days  on  its  face  it  will  be 
replaced  upon  its  back  with  the  thorax  and  pelvis  supported 
by  blocks,  and  the  dissectors  of  the  head  and  neck  should  at 
once  proceed  to  clean  the  temporal  fascia,  and  afterwards  to 
remove  the  brain  and  study  the  interior  of  the  cranium. 

Dissection. — Take  away  the  anterior  and  superior  auricular  muscles  and 
remove  the  thin  layer  of  fascia  subjacent  to  them  which  descends  from 
the  lower  border  of  the  galea  aponeurotica  to  the  zygomatic  arch.  When 
this  has  been  done  the  strong  temporal  fascia  will  be  exposed.  Note  that 
it  is  attached  above  to  the  temporal  ridge  and  below  to  the  upper  border 
of  the  zygomatic  arch.  The  details  of  its  connections  will  be  studied  at 
a  later  period. 


REMOVAL  OF  THE  BRAIN. 

After  the  superficial  attachments  of  the  temporal  fascia 
have  been  noted  the  dissectors  of  the  head  and  neck  should 
proceed  to  remove  the  brain. 

Dissection. — The  head  being  supported  upon  a  block,  extend  the  median 
incision,  already  made  in  the  galea  aponeurotica,  to  the  nasion  anteriorly  and 


REMOVAL  OF  THE  BRAIN 


20I 


to  the  external  occipital  protuberance  posteriorly,  and  cut  through  the  loose 
areolar  tissue  and  the  pericranium  in  the  same  line  down  to  the  bone. 
With  the  handle  of  the  scalpel,  or  with  a  chisel,  detach  the  pericranium  from 
the  bone  on  each  side  and  turn  it  posteriorly  and  downwards  to  the  temporal 
ridges,  leaving  the  bone  perfectly  bare.  Note  that  although  the  pericranium 
is  foosely  attached  over  the  surface  of  the  various  bones  of  the  vault,  it 
is  firmly  attached  along  the  lines  of  the  cranial  sutures  by  processes  that 
dip  in  between  the  bones  and  separate  their  edges.  Detach  the  galea 
aponeurotica  and  the  temporal  fascia  from  the  temporal  ridge  on  each  side 
with  the  edge  of  the  knife  ;  then  carrying  the  edge  of  the  knife  anteriorly  and 
posteriorly  between  the  temporal  muscle  and  the  bone  detach  the  upper 
part  of  the  muscle  from  the  skull.  When  this  has  been  done,  each  half  of  the 
scalp  can  be  turned  down  over  the  ear. 

The  dissectors  should  next  obtain  a  saw,  a  chisel,  and  a  mallet,  and 


Vein 


Sub-arachnoid  space  and  trabeculse 


~  Dura  mater 
-Subdural  space 
Wrachnoid 
■Pia  mater 


Fig.  82. — Diagi-ammatic  section  through  the  Meninges  of 
the  Brain.      (Schwalbe. ) 

CO.   Grey  matter  of  cerebral  g5n"i. 

proceed  to  remove  the  calvaria.  The  line  along  which  the  saw  is  to  be 
used  may  be  marked  out  on  the  skull  by  encircling  it  mth  a  piece  of  string, 
and  then  marking  the  cranium  with  a  pencil  along  the  line  of  the  string. 
Anteriorly,  the  cut  should  be  made  fully  three-quarters  of  an  inch  above  the 
margins  of  the  orbits  ;  posteriorly,  it  should  be  carried  round  at  the  level  of  a 
point  midway  between  the  lambda^  and  the  external  occipital  protuberance. 
The  saw  should  be  used  to  divide  the  outer  table  of  the  skull  only.  When 
the  diploe  is  reached,  the  sawdust  will  become  red  and  moist,  and  the  saw 
should  then  be  abandoned.  The  hammer  and  chisel  are  now  brought  into 
requisition,  and  by  short  sharp  strokes  with  these  the  inner  table  can 
readily  be  split  along  the  line  in  which  the  outer  table  of  the  cranium  is 
divided.  When  this  has  been  done,  insinuate  the  hook  at  the  end  of  the 
cross-bar  of  the  chisel  into  the  fissure  in  front,  and  wrench  off  the  skull-cap. 

Dura  Mater  Encepliali. — The   brain  is  clothed  by  three 
distinct  membranes,  which  are  termed  the  7?ieninges.     These 

^  The  term  "  lambda  "  signifies  the  apex  of  the  occipital  bone,  or  the  point 
at  which  the  sagittal  and  lambdoidal  sutures  meet. 


202  HEAD  AND  NECK 

are  from  without  inwards — (i)  the  dura  mater;  (2)  the 
arachnoid ;  and  (3)  the  pia  mater. 

When  the  skull-cap  is  detached,  the  outer  surface  of  the 
dura  mater,  as  it  covers  the  upper  surface  of  the  cerebral 
hemispheres,  is  exposed.  It  is  rough,  and  dotted  over  with 
bleeding  points.  If  a  portion  is  placed  in  water,  its  roughness 
becomes  still  more  manifest,  and  is  seen  to  be  due  to  a  multi- 
tude of  fine  fibrous  and  vascular  processes  by  which  it  is 
connected  with  the  deep  surface  of  the  bones.  These  have 
necessarily  been  torn  asunder  in  the  removal  of  the  skull- 
cap. The  bleeding  points  are  most  numerous  along  the 
median  line,  or,  in  other  words,  along  the  line  of  the  superior 
sagittal  sinus  (O.T.  longitudinal) ;  and  if  the  handle  of  the 
knife  is  run  from  before  backwards,  so  as  to  make  pressure 
along  this  line,  a  considerable  quantity  of  blood  will  ooze  out. 
This  shows  that  a  number  of  small  veins  from  the  cranial 
bones  have  been  ruptured.  The  degree  of  adhesion  between 
the  dura  mater  and  the  inner  surface  of  the  cranial  bones 
varies  in  different  subjects  and  in  different  localities.  In  all 
cases  it  is  strongly  adherent  along  the  lines  of  the  sutures,  like 
the  pericranium  externally;  and,  further,  it  is  much  more  firmly 
attached  to  the  base  than  to  the  vault  of  the  cranium.  In  the 
child — indeed,  as  long  as  the  bones  of  the  cranium  are  grow- 
ing— it  is  more  adherent  than  in  the  adult ;  and  it  is  more 
firmly  bound  to  the  bone  again  in  old  age. 

The  dissectors  should  now  clean  the  outer  surface  of  the 
dura  mater  with  a  sponge.  They  will  then  recognise  the  middle 
meningeal  artery  upon  each  side,  ascending  in  the  substance 
of  the  membrane,  and  sending  off  its  branches  in  a  widely 
arborescent  manner.  It  stands  out  in  bold  relief  from  the 
membrane.  If  the  skull-cap  is  examined,  its  inner  surface 
will  be  observed  to  be  deeply  grooved  by  the  branches 
of  the  artery  and  the  veins  which  accompany  and  lie  external 
to  them  (Wood  Jones).  The  meningeal  arteries  are  not 
intended  for  the  supply  of  the  membrane  alone,  as  the  name 
might  lead  one  to  imagine.  They  are  also  the  nutrient 
vessels  of  the  inner  table  and  diploe  of  the  cranial  bones. 

Granulationes  Arachnoideales  (O.T.  Pacchionian  Bodies). 
— These  granulations  are  almost  invariably  present,  and,  as  a 
rule,  are  best  marked  in  old  subjects.  They  are  small  granular 
bodies,  ranged  in  clusters  on  either  side  of  the  superior 
sagittal  (O.T.  longitudinal)  sinus,  into  which  many  of  them 


REMOVAL  OF  THE  BRAIN 


203 


protrude  (Fig.  83).  As  a  general  rule,  they  are  most  evident 
towards  the  posterior  part  of  the  parietal  region.  At  first  sight 
they  appear  to  be  protrusions  from  the  dura  mater,  but  this 
is  not  the  case.  They  spring  from  the  arachnoid  and  the  sub- 
arachnoid tissue,  and  are  enlargements  of  the  normal  villi  of 
the  membrane  (Fig.  84). 

Two  Layers  of  the  Dura  Mater. — Having  noted  these 
preliminary  details  from  an  examination  of  the  outer  surface 
of  the  dura  mater,  the  student  is  in  a  position  to  understand 
that  this  membrane  does  not  belong  entirely  to  the  brain. 
It  performs  a  double  function:  (i)  it  acts  as  an  internal 
periosteum  to  the  bones  forming  the  cranial  cavity ;  and  (2) 


Arachnoideal  granulation 


Opening  of  cerebral  vein 


Bone 


Fig.  83. — Median  section  through  the  Frontal  Bone  and  corresponding  part  of 
the  Superior  Sagittal  Blood  Sinus.  The  arachnoideal  granulations  are 
seen  protruding  into  the  sinus.      (Enlarged.) 

it  gives  support  to  the  different  parts  of  the  brain.  Conse- 
quently, it  consists  of  two  strata,  which,  in  most  localities,  are 
firmly  adherent,  but  they  can  usually  be  easily  demonstrated 
in  the  dissecting-room.  These  strata  may  very  appropriately 
be  termed  the  endocranial  and  the  supporting  layers.  Along 
certain  lines  these  two  layers  separate  from  each  other.  In 
some  cases  they  separate  so  as  to  form  blood  channels,  termed 
sinus  durce.  matris,  for  the  conveyance  of  venous  blood;  in 
other  cases  they  separate  in  order  that  the  inner  supporting 
layer  may  form  strong  folds  or  partitions,  which  pass  in 
between  certain  parts  of  the  brain  ;  and  by  these  partitions  the 
cranial  cavity  is  divided  into  compartments  communicating 
freely  with  one  another,  and  each  holding  a  definite  sub- 
division of  the  brain  (Fig.  87). 

Dissectio7i. — These  points  must  now  be  verified.     Begin  by  tilting  the 


204 


HEAD  AND  NECK 


head  forwards.  Support  it  in  this  position,  and  make  two  incisions  through 
the  dura  mater  in  an  antero-posterior  direction — one  on  each  side  of  the 
superior  sagittal  sinus,  and  along  its  whole  length.  From  the  mid- 
point of  each  of  these  incisions  another  cut  must  be  made  through  each 
lateral  portion  of  the  dura  mater  downwards  to  the  cut  margin  of  the  skull 
immediately  above  the  ear  (Fig.  85).  The  dura  mater  covering  the  upper 
aspect  of  the  brain  is  thus  divided  into  a  central  strip  containing  the 
superior  sagittal  sinus,  and  four  triangular  flaps.  The  flaps  should 
now  be  turned  downwards  over  the  cut  margin  of  the  skull,  and  in  this 
position  they  preserve  the  brain,  during  its  removal,  from  laceration  by  the 
sharp  bony  edge. 


Lateral  lacuna 
Arachnoideal 


Arachnoideal  granulation 


\«^. 


granulation  ^^^#'|^^^;S^^1^ 


Sagittal  sinus 


Lateral  lacuna 


Dura  mater 


Blood  vessels 
Grey  cortex 
of  a  gyrus    ^^ 


?Pia  mater 

'  Subarachnoid  space 

^Arachnoid 


Falx  cerebri 


Fig.  84. — Diagram  of  a  frontal  section  through  the  middle  portion  of  the 
cranial  vault  and  subjacent  brain  to  show  the  membranes  of  the  brain 
and  the  arachnoideal  granulations. 


Cavum  Subdurale. — The  subdural  space  is  the  term  applied 
to  the  interval  between  the  dura  mater  and  the  arachnoid — 
Figs.  S^  and  84.  It  contains  a  very  small  quantity  of  serous 
fluid,  which  moistens  the  opposed  surfaces  of  the  membranes. 
A  striking  contrast  between  the  two  surfaces  of  the  dura 
mater  will  be  noted.  The  external  surface  is  rough  and 
flocculent ;  the  internal  surface  is  smooth  and  glistening. 

Venae  Cerebri. — The  cerebral  veins  which  return  the  blood 
from  the  surface  of  the  cerebral  hemispheres  will  be  seen 
shining  through  the  arachnoid.  They  are  lodged  for  the 
most  part  in  the  sulci  between  the  gyri,  and  run  upwards 
to  the  median  plane.  When  they  reach  the  superior  sagittal 
sinus  they  turn  anteriorly,  and  lie  against  the  wall  of  the  sinus, 
for  some  distance,  before  they  open  into  it. 


REMOVAL  OF  THE  BRAIN 


205 


Sinus  Sagittalis  Superior  (O.T.  Superior  Longitudinal). — 

Open  into  this  venous  channel  by  running  the  knife  through 
its  upper  wall  from  behind  forwards  (Figs.  85  and  86).  It 
begins  anteriorly  at  the  crista  galli  of  the  ethmoid  bone, 
where  it  not  infrequently  communicates  with  the  veins  in 
the  nasal   cavity  through   the  foramen  caecum.      It  extends 


Frontal  air  sinus 


Cut  edge  of  superior 

sasfittal  sinus 


Cerebral  vein 

Lateral 
lacuna 


Arachnoid 
covering  cerebral   ^j' 
vein 


Cerebral  \u  , ' 


Dura  mater 


Anterior  branch  of 
mid.  meningeal  artery 
and  accompanying 
vein 


achnoideal 
granulation 

Posterior  branch 

of  mid.  meningeal 

rtery  with  vein 


Opening  of  a  superior 
cerebral  vein 


Fig.  85. — Superior  Sagittal  Sinus  ;   Dura  Mater  ;   Middle  Meningeal  Artery 
and  Veins  ;  Arachnoidea  and  Superior  Cerebral  Veins. 


posteriorly,  grooving  the  cranial  vault  in  the  median  plane,  to 
the  internal  occipital  protuberance,  on  the  right  aspect  of 
which  it  becomes  continuous  with  the  right  transverse  sinus 
(O.T.  lateral).  Its  lumen,  which  is  triangular  in  cross-section, 
is  very  small  anteriorly,  but  expands  greatly  posteriorly.  On 
either  side  of  the  sinus,  and  opening  into  it,  are  a  number  of 
clefts  between  the  two  layers  of  the  dura  mater ;  these  are 


2o6 


HEAD  AND  NECK 


the  lateral  lacunce.  The  inferior  angle  of  the  channel  is 
crossed  by  a  number  of  minute  bands,  named  chordce.  Willisii; 
and  arachnoideal  granulations  bulge  into  it.  The  mouths  of 
the  superior  cerebral  veins  open  into  the  sinus,  or  into  the 
lateral  lacunae,  pouring  their  blood  into  the  sinus  in  a  direc- 
tion contrary  to  that  in  which  the  blood  flows  within  the 

Falx  cerebri 

Inferior  sagittal  sinus 


Cavernous  sinus 


Auditory- 
tube 


Nasal 
septum 


Superior  sagittal 
sinus 


Vena  cerebri  magna 


Tentorium 

Straight 
sinus 


Transverse  smus 


Inferior  petrosal  sinus    Superior  petrosal  sinus 


Falx  cerebelli 
Transverse  sinus 


Fig.  86. — Sagittal  section  through  the  Skull  a  little  to  the  left  of  the 
median  plane  to  show  the  processes  of  Dura  Mater. 


V.  Trigeminal  nerve. 
VII.   Facial  nerve. 
VIII.  Acustic  nerve. 


IX.  Glossopharyngeal  nerve. 

X.  Vagus  nerve. 
XI.  Accessory  nerve. 
XII.  Hypoglossal  nerve. 


channel — that  is,  the  terminal  portions  of  the  veins  are  directed 
anteriorly,  whilst  the  blood  in  the  sinus  flows  posteriorly. 

The  Eelation  of  the  Arachnoideal  Granulations  to  the  Superior 
Sagittal  Sinus  and  the  Lateral  Lacunae. — When  the  granulations  push 
themselves  into  the  sinus  or  the  lateral  lacunae  they  push  before  them  a 
thin  continuous  covering  of  the  floor  of  the  space,  and  when  they  project 
still  further  and  encroach  upon  the  bones  of  the  skull  they  are  covered  also 
by  a  thin  expansion  of  the  roof  of  the  space. 

Falx  Cerebri  (Figs.  86,  87). — This  is  a  sickle-shaped  redupli- 
cation of  the  inner  layer  of  the  dura  mater,  which  descends 
in  the  median  plane,  between  the  two  cerebral  hemispheres. 


REMOVAL  OF  THE  BRAIN 


207 


In  order  to  expose  it,  the  cerebral  veins  must  be  divided  as 
they  open  into  the  superior  sagittal  sinus,  and  the  hemisphere 
gently  pulled  laterally.  Anteriorly,  the  falx  cerebri  is  narrow, 
and  attached  to  the  crista  galli  of  the  ethmoid  bone.  It 
increases  in  breadth  as  it  passes  backwards,  and  posteriorly 
it  is  attached  in  the  median  plane  to  the  upper  surface  of 
the  tentorium  cerebelli.  The  anterior  part  of  the  falx  is 
frequently  cribriform,  and  is  sometimes  perforated  by  apertures 
to  such  an  extent  that  it  almost  resembles  lace-work.     Along 


Superior  sagittal  sinus 


Cerebral 
fossa' 


Tentorium 


cerebri 


Cerebral 
fossa 


Transverse 

sinus  \"" 


Cerebellar  fossa 


Tentorium 
cerebelli 


Foramen  magnum  \        Transverse  sinus 
Cerebellar  fossa 


Fig.  87. — Frontal  section  through  the  Cranial  Cavity  in  a  plane  which  passes 
through  the  posterior  part  of  the  foramen  magnum.  The  posterior 
part  of  the  cranial  cavity,  from  which  the  brain  has  been  removed,  is 
depicted. 

each  border  its  two  layers  separate  to  enclose  a  blood-sinus. 
Along  its  upper  convex  margin  runs  the  superior  sagittal 
sinus ;  along  its  concave  free  border  courses  the  much  smaller 
inferior  sagittal  sinus  \  whilst  along  its  attachment  to  the 
tentorium  is  enclosed  the  straight  sinus.  Its  inferior  concave 
margin  overhangs  the  corpus  callosum,  with  which,  however, 
it  is  not  in  contact,  except  to  a  very  slight  extent,  posteriorly. 

Removal  of  the  Brain. — The  dissectors  should  now  proceed  to  remove 
the  brain.  Having  divided  the  attachment  of  the  falx  cerebri  to  the 
crista  galli,  pull  it  posteriorly.  Next,  removing  the  block  upon  which 
the  head  rests,  and  supporting  the  occiput  and  posterior  lobes  of  the  brain 
with  the  left  hand,  let  the  head  drop  well  downwards.  In  all  probability, 
the  frontal  lobes  will  fall  away  by  their  own  weight  from  the  anterior  fossa 


2o8  HEAD  AND  NECK 

of  the  base  of  the  cranium,  and  perhaps  carry  with  them  the  olfactory 
bulbs.  Should  they  remain  in  position,  however,  gently  raise  them  with 
the  fingers,  and  at  the  same  time  separate  the  olfactory  bulbs  from  the 
cribriform  plate  of  the  ethmoid  with  the  handle  of  the  knife.  As  the 
olfactory  bulbs  are  raised  the  minute  olfactory  nerves  which  spring  from 
them  and  perforate  the  cribriform  plate  of  the  ethmoid  bone  are  torn  across. 
The  large  round  and  white  optic  7ierves  (second  pair  of  cerebral  nerves)  now 
come  into  view,  as  they  leave  the  cranial  cavity  through  the  optic  foramina. 
When  these  are  divided,  the  internal  cajvtid  arteries  will  be  exposed,  and 
more  posteriorly,  in  the  median  plane,  the  infundibulum  will  be  seen  ;  it 
is  a  hollow  conical  process  which  extends  from  the  tuber  cinereum  at  the 
base  of  the  brain  to  the  hypophysis  (O.T.  pituitary  body),  which  lies  in 
the  fossa  hypophyseos  (O.T.  pituitary  fossa).  Divide  the  carotid  arteries 
and  the  infundibulum.  Posterior  to  the  infundibulum  is  the  upper 
border  of  the  dorsum  sellce,  terminating  on  each  side  in  the  rounded  posterior 
clinoid  process.  Passing  anteriorly  on  each  side  of  the  dorsum  selloe  is  the 
corresponding  third  cerebral  nerve,  which  must  not  be  touched  at  present. 
A  little  more  laterally,  and  on  a  slightly  lower  plane,  is  the  medial  or  free 
border  of  the  tentorium  cerebelli,  a  fold  of  the  inner  layer  of  the  dura  mater 
which  lies  above  the  cerebellum  and  forms  the  roof  of  the  posterior  fossa 
of  the  cranium. 

Carefully  displace  the  temporal  pole  of  the  brain  from  under  cover  of  the 
posterior  border  of  the  small  wing  of  the  sphenoid,  which  lies  to  the  lateral 
side  of  the  optic  nerve  and  the  cut  end  of  the  internal  carotid  artery  ;  then 
raise  the  temporal  lobe  from  the  floor  of  the  middle  fossa,  and  from  the 
upper  surface  of  the  tentorium  cerebelli.  Pass  the  knife  posterior  to  the 
dorsum  sellce,  immediately  above  the  level  of  the  third  cerebral  nerve,  and 
cut  through  the  midbrain,  as  it  ascends  from  the  posterior  fossa,  from  its 
lateral  surface  inwards  to  the  median  plane.  Repeat  the  operation  in  the 
same  way  on  the  opposite  side,  and  remove  the  cerebrum  and  upper  part  of 
the  midbrain  from  the  cranium.^ 

Place  the  removed  cerebrum  in  the  vault  of  the  cranium  and  lay  it  aside. 
Then  note  the  relative  positions  of  the  parts  exposed.  Anteriorly  lies  the 
floor  of  the  anterior  fossa  of  the  cranium  ;  behind  it,  on  a  more  depressed 
plane,  the  middle  fossa,  and  still  more  posteriorly  the  sloping  tentorium 
cerebelli. 

In  the  median  plane  anteriorly  is  the  projecting  crista  galli,  partially 
dividing  the  anterior  fossa  into  lateral  halves.  On  either  side  of  the  crista 
galli  is  the  depression  from  which  the  olfactory  bulb  was  dislodged,  and  still 
more  laterally  are  the  portions  of  the  floor  of  the  anterior  fossa  which  form 
the  roofs  of  the  orbits  ;  they  bulge  upwards  as  well-marked  convexities. 
Each  lateral  part  of  the  floor  of  the  anterior  fossa  terminates  posteriorly  in 
a  sharp  margin,  formed  by  the  posterior  border  of  the  small  wing  of  the 
sphenoid.  This  margin  overhangs  the  anterior  part  of  the  middle  fossa. 
It  is  covered  with  a  thickening  of  dura  mater  in  which  runs  the  spheno- 
parietal blood  sinus,  and  it  terminates  medially  in  a  projecting  process, 
the  anterior  clinoid  process.  On  the  medial  side  of  each  anterior  clinoid 
process  lie  the  corresponding  optic  nerve  and  internal  carotid  artery,  and 
springing  from  the  upper  surface  of  the  artery  is  its  ophthalmic  branch, 
which  runs  anteriorly  under  cover  of  the  optic  nerve.  Posterior  to  the 
divided  ends  of  the  internal  carotid  arteries,  and  in  the  median  plane,  is  the 
infundilDulum  descending  into  the  hypophyseal  fossa,  and  more  posteriorly, 
on  either  side,  are  the  projecting  posterior  clinoid  processes.  The  area 
between  the  four  clinoid  processes  is  covered  by  a  fold  of  the  inner  layer 

^  For  alternative  method  see  p.  217. 


REMOVAL  OF  THE  BRAIN 


209 


of  the  dura  mater,  termed  the  diaphragma  sellce.  In  its  centre  is  an 
aperture  through  which  the  infundibukmi  passes  to  join  the  hypophysis 
(O.T.  pituitary  body) ;  and  it  binds  down  the  hypophysis  in  the  fossa.  Jn  its 
anterior  and  posterior  margins,  respectively,  are  lodged  the  sinus_  inter- 
cavernosus  anterior  and  the  sinus  intercavernosus  posterior  (O.T.  circular 
sinus). 


Superior  sagittal  sinus 


Falx  cerebri 


Optic  nerve 

/ 
Ophthalmic  artery    </ 

IMaxillary  nerve.,/j 

Semilunar  ganglion 

Middle  meningeal 
arterj' 
Posterior  cerebral 
artery- 
Great  superficial  /' 
petrosal  nerve 

Pedunculus_ 
cerebri 

Substantia 
nigra 


Lamina , 
quadrigemina 


Cerebellum  " 


Straight  sinus 


Internal  carotid  artery 


-Infundibulum 

Cavernous  sinus 
Oculo-motor  nerve 


Basilar  arteiy 

Posterior  cere- 
bral artery 


Superior 
petrosal  sinus 


Trochlear  nerve 
"Basal  vein 

Transverse  sinus 
Great  cerebral  vein 


Fig.  88. — Interior  of  the  Cranium  after  the  remov^al  of  the  cerebrum.  The 
transverse,  straight,  and  superior  petrosal  sinuses  have  been  opened,  and 
the  dura  mater  has  been  removed  from  the  floor  of  the  middle  fossa. 

In  the  dura  mater,  on  each  side  of  the  hypophyseal 
(pituitary)  fossa,  Hes  the  corresponding  cavernous  sinus,  ^Yhich 
will  be  dissected  later,  and  still  more  laterally  are  the  de- 
pressed lateral  portions  of  the  middle  cranial  fossa,  lined  with 
dura  mater,  in  which  the  trunk  and  some  of  the  branches  of 


VOL,   II — 14 


2IO  HEAD  AND  NECK 

the  middle  meningeal  artery  are  visible.  Posterior  to  the 
middle  fossa  lies  the  tentorium  cerebelli  covering  the  cerebellum. 
The  peripheral  margin  of  the  tentorium  is  attached,  on  each 
side,  to  the  posterior  clinoid  process,  the  upper  margin  of  the 
petrous  part  of  the  temporal  bone,  the  posterior  inferior  angle 
of  the  parietal  bone,  and  to  the  transverse  ridge  on  the  inner 
surface  of  the  occipital  bone.  The  central  or  free  margin 
crosses  the  attached  margin  behind  the  posterior  clinoid 
process  on  each  side,  and  is  attached  anteriorly  to  the  apex 
of  the  anterior  clinoid  process.  It  bounds  an  oval  opening, 
the  door  of  the  tent,  through  which  pass  the  midbrain  sur- 
rounded by  the  arachnoid  and  the  pia  mater,  and  the  posterior 
cerebral  arteries.  Piercing  the  midbrain  nearer  its  posterior 
than  its  anterior  border  is  the  aquseductus  cerebri  (O.T. 
aqueduct  of  Sylvius),  Posterior  to  the  aqueduct  is  the  lamina 
quadrigemina  of  the  midbrain  and  anterior  to  it  the  pedun- 
culi  (O.T.  crura)  cerebri.  Each  peduncle  consists  of  an 
anterior  part,  the  basis  pedunculi  (O.T.  crusta\  and  a  posterior 
part,  the  tegmentu?n,  the  two  being  separated  by  a  lamina  of 
dark  coloured  tissue,  the  substantia  nigra.  The  bases  pedun- 
culi are  entirely  free  from  each  other,  but  the  tegmental 
portions  are  united  together  anterior  to  the  aqueduct. 

Running  anteriorl)^  and  laterally  from  the  medial  side  of 
each  peduncle  to  the  angle  between  the  anterior  ends  of  the  free 
and  the  attached  borders  of  the  tentorium,  is  the  third  cerebral 
nerve.  Close  to  the  midbrain  the  nerve  passes  between  the 
posterior  cerebral  artery  above  and  the  superior  cerebellar 
artery  below ;  and  between  the  free  and  attached  borders 
of  the  tentorium  it  pierces  the  dura  mater,  in  the  middle 
fossa,  and  enters  the  wall  of  the  cavernous  sinus.  Between 
the  posterior  ends  of  the  third  nerves  lies  the  upper  end  of 
the  basilar  artery,  dividing  into  the  two  posterior  cerebral 
branches;  and  the  dissectors  should  note  that  the  arteries 
lie  in  an  enlargement  of  the  subarachnoid  space  which  is 
known  as  the  cisterna  interpeduncularis.  In  the  median  plane 
posterior  to  the  midbrain  is  the  divided  vena  cerebri  magna 
(O.T.  great  vein  of  Galen).  It  passes  posteriorly  and  upwards, 
and  pierces  the  apex  of  the  tentorium  to  enter  the  straight 
sinus,  which  lies  in  the  angle  of  union  between  the  falx 
cerebri  and  the  tentorium  cerebelli. 

Curving  posteriorly  around  the  midbrain  and  ending 
posteriorly  in  the  great  cerebral  vein  on  each  side  is  the  vena 


REMOVAL  OF  THE  BRAIN  211 

basalis,  and  immediately  above  it,  running  anteriorly,  is  the 
slender  fourth  cerebral  nerve.  If  the  free  border  of  the 
tentorium  is  turned  laterally,  at  the  point  where  it  is  crossing 
the  attached  border,  the  fourth  nerve  will  be  seen  perforating 
the  inner  layer  of  the  dura  mater  to  enter  the  wall  of  the 
cavernous  sinus. 

When  the  dissectors  have  verified  the  facts  noted  above, 
they  should  examine  the  lower  free  border  of  the  falx  cerebri, 
in  which  they  will  find  the  small  inferior  sagittal  sinus,  which 
terminates  posteriorly,  at  the  apex  of  the  tentorium,  in  the 
straight  sinus.  The  straight  sinus  must  now  be  opened  by 
carrying  the  knife  posteriorly  through  the  falx  cerebri  along 
its  line  of  union  with  the  tentorium.  Then  the  falx  cerebri 
must  be  cut  away  from  the  occipital  bone,  and  as  this  is  done 
the  posterior  part  of  the  superior  sagittal  sinus  will  be  opened 
up.  After  the  falx  has  been  removed  the  right  and  left 
transverse  and  the  right  and  left  superior  petrosal  sinuses  must 
be  opened  by  incisions  carried  along  the  attached  border  of 
the  tentorium  (Fig.  88).  The  dissectors  will  probably  find 
that  the  superior  sagittal  sinus  turns  to  the  right  and  becomes 
continuous  with  the  right  transverse  sinus,  whilst  the  posterior 
end  of  the  straight  sinus  turns  to  the  left  and  joins  the  left 
transverse  sinus.  In  a  certain  number  of  cases  this  arrange- 
ment is  reversed,  and  not  uncommonly,  as  in  the  specimen 
shown  in  Fig.  88,  there  is  a  communication  between  the 
right  and  left  transverse  sinuses  across  the  front  of  the  internal 
occipital  protuberance.  Occasionally  the  superior  sagittal, 
the  two  transverse  sinuses,  the  straight  sinus,  and  the  occi- 
pital sinus  unite  anterior  to  the  internal  occipital  protuber- 
ance in  a  common  dilatation,  the  confluens  siniiiwi  (O.T. 
torcular  Herophili).  The  transverse  sinus,  on  each  side,  runs 
from  the  internal  occipital  protuberance  to  the  lateral  end  of 
the  superior  border  of  the  petrous  part  of  the  temporal  bone, 
where  it  dips  downwards  into  the  posterior  fossa,  and  at  the 
same  point  it  is  joined  by  the  superior  petrosal  sinus,  which 
runs  postero-laterally  along  the  superior  border  of  the  petrous 
part  of  the  temporal  bone  from  the  cavernous  sinus  to  the 
transverse  sinus,  connecting  the  two  together. 

Dissection. — With  the  point  of  the  scalpel  open  the  spheno-parietal 
sinus,  which  runs  along  the  posterior  border  of  the  small  wing  of  the 
sphenoid,  and  trace  it  medially  to  the  cavernous  sinus,  but  do  not  open  the 
latter.  Then  remove  the  dura  mater  from  the  lateral  part  of  the  middle 
fossa  on  one  side  to  expose  the  semilunar  (O.T.  Gasserian)  ganglion  of  the 
ir — 14  a 


2  12  HEAD  AND  NECK 

fifth  nerve,  the  middle  meningeal  artery  and  its  two  terminal  branches,  the 
accessory  meningeal  artery,  if  it  is  present,  and  the  great  superficial  petrosal 
nerve.  Commence  immediately  to  the  lateral  side  of  the  anterior  part  of 
the  free  border  of  the  tentorium,  where  a  cut  through  the  inner  layer  of  the 
dura  will  open  into  a  space  (O.T.  Meckel's  cave)  between  the  two  layers  of 
the  dura,  in  which  lies  the  semihmar  ganglion.  From  the  postero-medial 
border  of  the  ganglion  ih.e  posterior  branch  or  sensory  root  passes  backwards 
into  the  posterior  fossa  to  enter  the  pons  ;  and  from  its  anterior-lateral  border 
the  ophthalmic  branch  passes  upwards  and  anteriorly  in  the  lateral  wall  of 
the  cavernous  sinus,  the  maxillary  brajtch  runs  anteriorly  to  the  foramen 
rotundum,  and  the  mandibtdar  branch  passes  downwards  into  the  foramen 
ovale.  By  theside  of  the  mandibular  nerve  the  accessory  meningealarterymay 
be  found  entering  the  cranium ;  and  a  little  further  posteriorly  the  middle  men- 
ingeal artery  will  be  seen  passing  into  the  middle  fossa  through  the  foramen 
spinosum.  After  entering  the  cranium  the  middle  meningeal  artery  runs 
anteriorly  and  laterally,  across  the  floor  of  the  middle  fossa,  towards  the 
lateral  wall  and  divides  into  an  anterior  and  a  posterior  branch  ;  the  former 
ascends  on  the  anterior  part  of  the  lateral  wall  to  the  anterior  inferior  angle 
of  the  parietal  bone,  and  the  latter  runs  posteriorly  and  laterally,  and  then 
ascends  on  the  inner  surface  of  the  squamous  part  of  the  temporal  bone. 
The  great  superficial  petrosal  nerve  appears  on  the  anterior  surface  of  the 
petrous  part  of  the  temporal  bone  through  the  hiatus  Jtervi  facialis,  which 
lies  to  the  medial  side  of  the  e??iinentia  arcuata.  It  runs  anteriorly  and 
medially  and  disappears  beneath  the  semilunar  ganglion. 

After  the  structures  mentioned  above  have  been  found 
and  cleaned,  the  dissectors  must  remove  the  tentorium  cere- 
belli.  Cut  through  the  free  border  immediately  posterior  to 
the  point  where  it  crosses  the  attached  border;  the  fourth  nerve 
also  will  be  divided  by  this  incision.  Repeat  the  incision  on 
the  opposite  side,  and  then  cut  through  the  membrane  close 
to  its  attached  border,  but  to  the  medial  sides  of  the  superior 
petrosal  and  transverse  sinuses  j  next  divide  the  venae  basales 
at  their  points  of  junction  with  the  vena  cerebri  magna 
(O.T.  vein  of  Galen) ;  then  raise  the  anterior  part  of  the 
tentorium  and,  passing  the  knife  beneath  it,  separate  it  from 
the  falx  cerebelli,  which  is  attached  to  its  lower  surface  in  the 
median  plane.  The  tentorium  may  now  be  lifted  out  and  the 
arachnoid  covering  the  upper  surface  of  the  cerebellum  will 
be  exposed. 

After  the  upper  surface  of  the  cerebellum  has  been  cleaned, 
cut  through  the  third  cerebral  nerves,  and  then  press  back- 
wards the  pedunculi  cerebri  and  the  pons  (Varolii),  which  lies 
immediately  below  them,  to  expose  the  fifth  and  the  sixth 
nerves.  Cut  the  fifth  nerves  as  they  cross  the  upper  borders 
of  the  petrous  parts  of  the  temporal  bones,  and  then  divide 
the  small  sixth  nerves,  which  lie  more  medially  and  at  a 
slightly  deeper   level.     Press   the  pons  and   cerebellum  still 


REMOVAL  OF  THE  BRAIN 


213 


further  back  and  divide  the  seventh  and  eighth  nerves  as 
they  enter  the  internal  acustic  meatus.  Below  the  eighth 
nerves  lie  the  ninth,  tenth,  and  eleventh  nerves.     These  also 


Anterior  and  posterior  intercavernous  sinuses 
Ophthalmic  artery  '. 

Internal  carotid 
Tent.  Cerebelli  ant.  end  of 
attached  border 

Tent,  cerebelli  ant.  end 
of  free  border 

Spheno-parietal  sinus 
Inferior  petrosal  sinus   ; 
Superior 
petrosal  sinus , 
Middle     / 
meningeal  \  / 
artery  X, 


Infundibulum 
:  Diaphragma  sellae 

■  Optic  nerve 

Oculo-motor  nerve 

Vbducent  nerve 

Trochlear  nerve 

Trigeminal  nerve 
Facial  nerve 

^custic  nerve 


Sigmoid  part  o 
transverse  sinus 

Basilar  plexus'  \ 


Vertebral  artery 

Ligamentum  denticulatum 

Occipital  sinus  ' 

Transverse  sinus 


Gosso- 

pharyngeal 

nerve 


Vagus  nerve 


Accessory  nerve 
Hypoglossal  nerve 
First  cervical  nerve 
Spinal  medulla 


Fig.  89. — Dissection  of  the  Interior  of  the  Cranium  after  the  remova.1  of  the 
Brain  and  the  Tentorium  CerebelH. 


must  be  cut ;  and  the  roots  of  the  twelfth  nerves,  which  lie 
deeper  and  more  medially,  must  be  identified  and  divided. 
The  pons  can  then  be  displaced  still  further  posteriorly  and 
the  front  of  the  medulla  oblongata  will  be  brought  into 
11—14  h 


214 


HEAD  AND  NECK 


view.  Pass  the  knife  downwards,  anterior  to  the  medulla 
oblongata,  into  the  vertebral  canal,  and,  cutting  firmly  back- 
wards and  laterally,  on  each  side,  divide  the  medulla  spinalis 
and  the  vertebral  arteries.  Withdraw  the  knife,  pass  two 
fingers  downwards  anterior  to  the  medulla  oblongata  and  lift 
it  and  the  pons  and  the  cerebellum  out  of  the  posterior  fossa. 
Place  these  lower  parts  of  the  brain,  which  collectively 
constitute   the  hind   brain,   with  the  hemispheres  previously 


Oculo-motor  nerve 


Trochlear  nerve 

Sensory  root  of  the  trigeminal  nerve 
Motor  root  of  the  trigeminal 
nerve 

Abducent  nerve 


Motor  root  of  facial 
Cut  edge  of  the 
tentorium 


ip-'— Sensory  root  of 
'''I    facial  nerve 
Acustic  nerve 


_  Right  transverse 

sr 

;S-^Glosso-pharyngeal 
nerve 
Vagus  nerve 

Accessory  nerve 

Vertebral  artery 
Hypoglossal  nerve 
First  spinal  nerve 
Accessory  nerve 


Fig.  90. — Section  through  the  Head  a  little  to  the  right  of  the  Median 
Plane.  It  shows  the  posterior  cranial  fossa  and  the  upper  part  of  the 
vertebral  canal  after  the  removal  of  the  brain  and  the  medulla  spinalis. 


removed,  and  then  examine  the  cut  ends  of  the  cerebral  nerves 
and  the  blood  sinuses  which  lie  in  the  region  of  the  posterior 
fossa. 

In  the  upper  end  of  the  vertebral  canal  lies  the 
upper  extremity  of  the  severed  medulla  spinalis,  attached 
on  either  side  to  the  margin  of  the  foramen  magnum  by 
the  uppermost  dentation  of  the  ligamentum  denticulatum. 
Anterior  to  the  ligamentum  denticulatum,  on  each  side,  is 
the  vertebral  artery,  and  still  more  anteriorly,  on  a  slightly 
deeper  plane,  the  fila  of  the  anterior  root  of  the  first  cervical 


REMOVAL  OF  THE  BRAIN  215 

nerve  may  be  distinguished.  At  a  higher  level  on  each  side 
the  two  rootlets  of  the  hypoglossal  nerve  pierce  the  dura,  as 
they  pass  into  the  hypoglossal  canal  (O.T.  anterior  condyloid 
foramen).  The  spinal  root  of  the  accessory  nerve  passes 
through  the  foramen  magnum  into  the  cranium,  posterior  to 
the  ligamentum  denticulatum,  and,  turning  laterally  over 
the  margin  of  the  foramen  magnum,  it  joins  the  cerebral 
fibres  of  the  accessory  and  the  tenth  nerve,  with  which  it 
passes  through  an  aperture  in  the  dura  opposite  the  jugular 
foramen.  Immediately  above  the  eleventh  and  tenth  nerves 
the  smaller  trunk  of  the  ninth  nerve  pierces  the  dura.  Above 
the  ninth  nerve  the  eighth  nerve  and  the  motor  and  sensory 
roots  of  the  seventh  nerve  pass  into  the  internal  acustic 
meatus,  accompanied  by  the  small  auditory  branch  of  the 
basilar  artery  and  the  auditory  vein.  The  two  roots  of  the 
seventh  nerve  lie  in  a  groove  on  the  upper  and  anterior 
aspect  of  the  eighth,  the  small  sensory  root  (O.T.  pars 
intermedia)  being  situated  between  the  motor  root  and  the 
eighth  nerve.  The  small  motor  and  the  large  sensory  root 
of  the  fifth  nerve  pass  through  an  opening  in  the  dura  which 
lies  above  and  medial  to  the  internal  acustic  meatus  ;  and  the 
sixth  nerve  pierces  the  dura  mater  below  and  to  the  medial 
side  of  the  opening  for  the  fifth  nerve,  opposite  the  side  of 
the  base  of  the  dorsum  sellse.  The  small  fourth  nerve 
pierces  the  under  surface  of  the  free  border  of  the  tentorium 
at  the  point  where  it  is  crossing  the  attached  border. 

After  the  dissectors  have  familiarised  themselves  with  the 
positions  of  the  cerebral  nerves  as  they  pierce  the  dura  mater, 
they  should  examine  the  falx  cerebelli  and  complete  the 
display  of  the  cranial  blood  sinuses. 

The  Falx  Cerebelli  is  a  small  sagittal  fold  of  the  inner 
layer  of  the  dura  mater  which  projects  anteriorly,  between  the 
lateral  lobes  of  the  cerebellum,  from  the  internal  occipital 
crest  (Figs.  87,  89). 

Sinus  Transversus  (O.T.  Lateral). — The  horizontal  part  of 
the  transverse  sinus  has  already  been  traced  from  the  internal 
occipital  protuberance  to  the  superior  border  of  the  petrous 
part  of  the  temporal  bone,  where  it  turns  downwards  to 
the  jugular  foramen.  At  first  the  descending  portion  runs 
downwards,  on  the  inner  surface  of  the  mastoid  part  of  the 
temporal  bone,  and  then  anteriorly  and  again  downwards 
across  the  upper  and  anterior  surfaces  of  the  jugular  process 

n— 14c 


2i6  HEAD  AND  NECK 

of  the  occipital  bone.  On  account  of  the  sinuosity  of  its 
course  this  part  is  called  the  sigmoid  portion  of  the  transverse 
sinus.  Open  this  part  of  the  sinus  and  find  the  mouth  of  the 
mastoid  emissary  vein  in  its  posterior  border  about  half-way 
down. 

The  dissectors  should  now  obtain  the  basal  part  of  a 
macerated  skull  and  should  note  the  relation  of  the  transverse 
sinus  to  the  outer  surface.  They  will  find  that  the  position 
of  the  sinus  can  be  indicated  on  the  external  surface,  by  a  line 
which  commences  at  the  external  occipital  protuberance,  passes 
forwards,  with  a  slight  upward  convexity,  along  the  superior 
nuchal  line  to  the  upper  part  of  the  mastoid  part  of  the 
temporal  bone  and  then  descends  to  the  level  of  the  lower 
margin  of  the  external  meatus. 

Sinus  Occipitalis. — The  occipital  sinus  is  not  uncommonly 
absent.  When  it  is  present  it  commences  in  the  right  or  left 
transverse  sinus  or  the  confluens  sinuum,  and  descends  for  a 
short  distance  in  the  posterior  border  of  the  falx  cerebelli.  It 
terminates  below  in  two  lateral  branches,  which  leave  the  falx 
cerebelli  and  run  along  the  borders  of  the  foramen  magnum 
between  the  layers  of  the  dura  mater,  to  terminate  anteriorly 
in  the  lower  ends  of  the  transverse  sinuses. 

Sinus  Petrosus  Inferior. — The  inferior  petrosal  sinus  lies 
along  the  posterior  angle  of  the  petrous  part  of  the  temporal 
bone  extending  from  a  point  lateral  to  the  opening  for  the 
sixth  nerve  to  the  medial  side  of  the  opening  in  the  dura 
for  the  ninth  nerve  of  the  same  side.  Lay  the  sinus  open. 
It  opens  anteriorly  into  the  cavernous  sinus,  from  which  it 
receives  blood,  and  it  passes  posteriorly  through  the  jugular 
foramen  to  join  the  upper  end  of  the  internal  jugular  vein. 

Plexus  Basilaris. — The  two  inferior  petrosal  sinuses  are 
connected  together  across  the  upper  surface  of  the  basilar 
part  of  the  occipital  bone  by  a  plexus  of  small  venous  channels, 
to  which  the  term  basilar  plexus  is  applied.  Unless  these 
channels  happen  to  be  distended  with  blood  the  dissectors  will 
probably  be  unable  to  display  this  plexus. 

The  dissectors  should  note  that  the  dura  mater  is  much 
more  firmly  attached  to  the  bones  of  the  base  than  it  was  to 
the  bones  of  the  vertex,  a  fact  which  should  have  attracted 
their  attention  as  they  removed  the  membrane  from  the  floor 
of  the  middle  fossa.  They  should  note  also  that  it  gives 
sheaths  to  the  nerves  which  pierce  it,  and  that  at  the  margins 


REMOVAL  OF  THE  BRAIN  217 

of  the  various  foramina  its  outer  layer  becomes  continuous 
with  the  periosteum  on  the  outer  surface  of  the  cranium, 
whilst  at  the  margin  of  the  foramen  magnum  the  inner  layer 
becomes  continuous  with  the  single  layer  of  dura  mater  which 
surrounds  the  medulla  spinaUs  ;  and  that  at  the  same  level  the 
arachnoid  and  pia  mater  of  the  brain  become  continuous  with 
the  arachnoid  and  pia  mater  of  the  spinal  medulla  (O.T.  spinal 
cord).  Before  terminating  the  survey  of  the  interior  of  the 
cranium  the  dissectors  should  revise  their  knowledge  of  the 
blood  vessels,  and  their  relations  to  the  dura  mater ;  and  they 
should  remove  the  hypophysis  (O.T.  pituitary  body)  and  in- 
vestigate its  naked-eye  structure. 

Sinus  Durse  Matris. — Four  blood  sinuses  lie  t?i  the  median 
plane:  (i)  the  superior  sagittal  sinus  in  the  upper  or  attached 
border  of  the  falx  cerebri ;  (2)  the  inferior  sagittal  sinus  in  the 
free  part  of  the  lower  border  of  the  falx  cerebri ;  (3)  the 
straight  sinus  along  the  line  of  attachment  of  the  falx  cerebri 
with  the  tentorium  cerebeUi;  (4)  the  occipital  sinus  in  the 
upper  part  of  the  attached  border  of  the  falx  cerebeUi. 

Two  sinuses  lie  in  a  higher  horizontal  plane :  these  are  the 
spheno-parietal  sinuses,  which  run  along  the  posterior  borders 
of  the  small  wings  of  the  sphenoid  bone. 

Six  sinuses  lie  in  a  lower  horizontal  plane:  (i)  the  two 
cavernous  sinuses  at  the  sides  of  the  body  of  the  sphenoid ; 
(2)  the  two  superior  petrosal  sinuses  along  the  upper  angles 
of  the  petrous  parts  of  the  temporal  bones,  in  the  anterior 
parts  of  the  attached  border  of  the  tentorium  cerebeUi;  (3) 
the  horizontal  parts  of  the  transverse  sinuses  in  the  posterior 
parts  of  the  attached  border  of  the  tentorium.  The  terminal 
parts  of  the  transverse  sinuses  descend  along  the  anterior  parts 
of  the  lateral  walls  of  the  posterior  fossa. 

Two  sinuses  ritfi  obliquely  downwards^  posteriorly^  and  later- 
ally :  these  are  the  two  inferior  petrosal  sinuses. 

Three  sinuses  run  transversely  connecting  paired  sinuses  of 
opposite  sides:  (i)  the  anterior  intercavernous  sinus  in  the 
anterior  border  of  the  diaphragma  seUae ;  (2)  the  posterior 
intercavernous  sinus  in  the  posterior  border  of  the  diaphragma 
sellae;  and  (3)  the  basUar  plexus  which  connects  together  the 
inferior  petrosal  sinuses  across  the  upper  surface  of  the  basilar 
part  of  the  occipital  bone. 

Alternative  Method  of  Removing  the  Brain. — If  it  is  thought 
desirable  to  remove  the  brain  entire  by  the  more  rapid  but  less  instructive 


2i8  HEAD  AND  NECK 

method  usually  adopted  in  the  post-mortem  room,  then  the  following  steps 
should  be  taken  after  the  falx  cerebri  has  been  detached  from  the  crista 
galli  and  the  dura  mater  lining  the  vault  of  the  cranium  has  been  thrown 
aside  (see  p.  204). 

Remove  the  block  upon  which  the  head  has  been  resting,  and,  support- 
ing the  occiput  and  the  posterior  part  of  the  brain  with  the  left  hand,  let 
the  head  drop  well  downwards  and  in  all  probability  the  weight  of  the 
frontal  lobes  will  draw  them  away  from  the  floor  of  the  anterior  fossa  of 
the  skull,  and  possibly  the  olfactory  lobes  may  be  carried  with  them.  If 
the  olfactory  bulbs  remain  in  position  on  the  cribriform  plates  of  the 
ethmoid  at  the  sides  of  the  crista  galli,  gently  raise  them  with  the  handle 
of  the  scalpel  and  press  them  backwards  on  to  the  under  surfaces  of  the 
frontal  lobes.  As  the  olfactory  bulbs  are  raised  the  olfactory  nerve  fila- 
ments which  pass  from  their  lower  surfaces  through  the  cribriform  plates 
are  torn.  As  the  frontal  lobes  are  pressed  backwards  the  large  round 
and  white  optic  nerves  come  into  view  as  they  are  leaving  the  cranial  cavity 
through  the  optic  foramina.  When  these  are  divided  the  internal  carotid 
arteries  will  be  exposed,  and  more  posteriorly  in  the  median  plane  lies  the 
infundibulum,  a  hollow  conical  process  which  connects  the  hypophysis 
cerebri  {O.T.  pittcitary  body)  with  the  tuber  cinereum  at  the  base  of  the 
brain,  and  more  laterally  are  the  octdo-viotor  nerves.  Sever  each  of  these 
structures  in  turn.  On  the  lateral  side  of  each  third  nerve  lies  the  medial 
or  free  border  of  the  tentorium  cerebelli  passing  anteriorly  to  be  attached  to 
the  anterior  clinoid  process.  Turn  this  margin  aside  with  the  point  of  the 
knife,  and  the  minute  trochlear  nerve  (fourth  cerebral  nerve)  will  be  brought 
into  view.  It  lies  under  shelter  of  the  free  border  of  the  tentorium,  and 
should  be  divided  at  this  stage.  The  head  must  in  the  next  place  be  turned 
forcibly  round,  so  that  the  face  is  directed  over  the  left  shoulder.  Raise 
the  posterior  part  of  the  right  cerebral  hemisphere  with  the  fingers,  and 
note  that  it  rests  upon  the  tentorium  cerebelli — a  broad  horizontal  process 
of  dura  mater  which  intervenes  between  it  and  the  cerebellum.  Divide 
the  tentorium  along  its  attached  border,  and  take  care  whilst  doing  this 
not  to  injure  the  subjacent  cerebellum.  Now  turn  the  head  so  as  to  bring 
its  left  side  uppermost,  and  treat  the  tentorium  on  that  side  in  the  same 
manner.  The  two  parts  of  the  trigeminal  nerve  (fifth  cerebral  nerve)  per- 
forating the  dura  mater  near  the  apex  of  the  petrous  portion  of  the  temporal 
bone  ;  the  abducent  nerve  (sixth  cerebral  nerve)  piercing  the  dura  mater 
behind  the  dorsum  sellae  of  the  sphenoid  bone  ;  the  facial  nerve  and  the 
acustic  nerve  disappearing  into  the  internal  acustic  meatus  ;  the  glosso- 
pharyngeal^ the  vagus,  and  the  accessory  nerves  leaving  the  skull  through 
the  jugular  foramen  ;  and  the  two  slips  of  the  hypoglossal  nerve  piercing  the 
dura  mater  over  the  hypoglossal  canal  (O.T.  anterior  condyloid  foramen), 
will  each  in  turn  come  into  view  upon  either  side,  and  must  be  divided  in 
succession.  In  the  case  of  the  three  nerves  passing  out  of  the  cranium 
through  the  jugular  foramen,  the  dissector  should  endeavour  to  leave  the 
accessory  of  the  right  side  intact  within  the  cranium,  by  dividing  its  roots 
of  origin  from  the  medulla  oblongata,  whilst  on  the  other  side  he  should 
remove  it  with  the  brain.  This  nerve  is  readily  recognised  because  it 
ascends  from  the  vertebral  canal  into  the  cranial  cavity  through  the  foramen 
magnum.  Now  thrust  the  knife  into  the  vertebral  canal,  and  divide  the 
medulla  spinalis  and  the  vertebral  arteries,  as  they  turn  anteriorly  upon 
the  upper  part  of  the  medulla  spinalis  (O.T,  spinal  cord) ;  then  sever  the 
accessory  nerve  of  the  left  side,  and  the  roots  of  the  first  pair  of  spinal 
nerves.  When  this  has  been  done  let  the  head  fall  well  downwards,  gently 
dislodge  the  medulla  oblongata  and  cerebellum,  and  the  whole  brain  can 
be  removed.      The  vena  cerebri  magna  (Galen),   as  it  passes  from  the 


REMOVAL  OF  THE  BRAIN  219 

interior   of  the   brain    to   enter   the    straight   sinus,   is    ruptured    by   this 
proceeding. 

Meningeal  Veins. — In  addition  to  the  named  blood  sinuses,  venous 
channels  accompany  the  meningeal  arteries  and  more  particularly  the 
trunks  and  branches  of  the  middle  meningeal  artery.  These  vessels  are 
of  wider  calibre  than  the  corresponding  arteries,  and  lie  external  to  them 
in  the  grooves  on  the  inner  surfaces  of  the  cranial  bones.  When  the 
arteries  are  distended  they  compress  the  middle  parts  of  the  veins  and 
drive  the  blood  into  their  anterior  and  posterior  margins.  When  this 
occurs  each  artery  appears  to  be  accompanied  by  two  veins,  a  circumstance 
which  is  probably  responsible  for  the  statement  that  some  of  the  meningeal 
arteries  have  venae  comites. 

Emissaria.  —  Emissary   veins    are    blood    channels    which 
connect  the  sinuses  of  the  dura  mater  with  the  veins  which 
lie  outside  the  cranium.     They  are:   (i)  Emissary  veins  con- 
nected with  the  superior  sagittal  sinus — (a)  from  the  anterior 
extremity    of  the    sinuses    an   emissary  vein   passes   through 
the   foramen   caecum.     This   vein   divides   below   and  either 
becomes  continuous  with  the  veins  of  the  nasal  fossae,  or  its 
branches  pass  through  foramina  in  the  nasal  bones  and  join 
the    angular    veins ;    {b)  two   parietal   emissary   veins,   which 
pass  through  the  parietal  foramina  and  connect  the  superior 
sagittal  sinus  with   the   occipital  veins,     (2)  Emissary  veins 
connected    with    the    transverse    sinuses  —  {a)    two    mastoid 
emissary  veins,  one  on  each  side,  pass  through  the  mastoid 
foramina   and   connect   the   sigmoid   parts   of  the   transverse 
sinuses    with    the    posterior    auricular    veins ;    (b)   two    post- 
condyloid  veins,  one  on  each  side,  pass  through  the  condyloid 
canals  and  connect  the  lower  ends  of  the  transverse  sinuses 
with  the  plexuses  of  veins  in  the  suboccipital  triangles.     (3) 
Emissary  veins  connected  with  the  cavernous  sinuses — {a)  a 
vein  which  traverses  the  foramen  ovale,  or  the  foramen  Vesalii, 
and  connects  the  cavernous  sinus  with  the  plexus  of  veins 
around  the  external  pterygoid  muscle ;  {p)  a  plexus  of  veins 
which  passes   through   the  temporal   bone  with  the   internal 
carotid   artery   and    connects   the   cavernous   sinus   with    the 
pharyngeal    venous    plexus ;   (c)  in    a   sense    the   ophthalmic 
vein  may  be  considered  an  emissary  vein,  for  although  under 
ordinary  circumstances  it  is  a  tributary  of  the  sinus,  blood  can 
flow  through  it  in  the  opposite  direction  from  the  sinus  into 
the  orbit,  and  then  along  the  tributaries  which  connect  the 
ophthalmic  vein  with  the  angular  vein,  and  along  the  channels 
which    connect    the    ophthalmic    vein    through    the    inferior 
orbital  fissure  with  the  veins  in  the  infratemporal  region. 


2  20    .  HEAD   AND  NECK 

The  Arteries  of  the  Cranial  Cavity. — (i)  The  vertebral 
arteries;  (2)  the  internal  carotid  arteries;  (3)  the  meningeal 
arteries. 

Arterise  Vertebrales. — The  vertebral  arteries  pierce  the 
spinal  dura  mater  below  the  foramen  magnum,  through  which 
they  enter  the  cranium.  As  each  artery  passes  through  the 
foramen  it  lies  anterior  to  the  highest  dentation  of  the  liga- 
mentum  denticulatum,  and  it  passes  between  the  hypoglossal 
and  first  cervical  nerves.  It  was  divided  when  the  hind  brain 
was  removed,  and  its  cut  extremity  lies  near  its  point  of 
entrance  into  the  cranial  cavity. 

Arterise  Carotides  Internse. — Each  internal  carotid  artery 
enters  the  cranium  at  the  lacerate  foramen  between  the  apex 
of  the  petrous  part  of  the  temporal  bone  and  the  body  of  the 
sphenoid,  where  it  pierces  the  outer  layer  of  the  dura  mater. 
Then  it  runs  anteriorly  in  the  cavernous  sinus  to  the  medial 
side  of  the  anterior  clinoid  process,  where  it  turns  upwards, 
pierces  the  inner  layer  of  the  dura  mater  and  the  arachnoid, 
and  gives  off  its  ophthalmic  branch,  which  runs  anteriorly  below 
the  optic  nerve  to  the  orbit.  The  artery  was  cut  immediately 
behind  its  ophthalmic  branch  during  the  early  stages  of  the 
removal  of  the  brain. 

Meningeal  Arteries. — These  are  the  nutrient  arteries  of 
the  dura  mater,  and  of  the  inner  table  and  diploe  of  the  cranial 
bones.  They  are  derived  from  a  great  number  of  different 
sources,  but  the  only  one  of  any  size  is  the  7niddle  meningeal 
branch  of  the  internal  maxillary  artery.  The  others  are 
small  twigs,  and,  except  in  a  well  -  injected  subject,  will 
not  be  easily  made  out.  They  are:  (i)  a?iterior  meningeal 
from  the  anterior  ethmoidal  artery ;  (2)  the  accessory  meningeal 
from  the  internal  maxillary  artery;  (3)  some  small  branches  from 
the  ascending  pharyngeal,  occipital,  and  vertebral  arteries. 

Each  middle  meningeal  artery  is  a  branch  of  the  corre- 
sponding internal  maxillary  artery.  It  enters  the  cranium 
through  the  foramen  spinosum  of  the  sphenoid,  and  divides 
upon  the  inner  surface  of  the  great  wing  of  that  bone  into  two 
large  terminal  branches.  Of  these,  the  anterior  branch  ascends 
upon  the  great  wing  of  the  sphenoid,  and  the  anterior 
inferior  angle  of  the  parietal  bone,  grooving  both  deeply, 
whilst  the  posterior  branch  turns  posteriorly  upon  the 
squamous  portion  of  the  temporal  bone.  The  branches 
which    proceed    from   these   trunks    spread   out   widely  and, 


REMOVAL  OF  THE  BRAIN 


22  I 


with  the  accompanying  venous  channels,  occupy  the  arbor- 
escent grooves  on  the  inner  surface  of  the  cranial  vault. 

The  vein  which  accompanies  the  middle  meningeal  artery 
passes  through  the  foramen  spinosum  and  ends  in  the  plexus 
around  the  external  pterygoid  muscle. 

Each  anterior  meningeal  artery  proceeds  from  the  anterior 
ethmoidal  artery  as  it  accompanies  the  anterior  ethmoidal 
nerve  across  the  cribriform  plate  of  the  ethmoid  bone. 
It  supplies  a  limited  area  of  dura  mater  and  bone  in  the 
anterior  fossa  of  the  cranium. 

The  accessory  7neningeal  arteries  (O.T.  small  mefiingeat)  are 
somewhat   inconstant ;    they  arise   either   directly   from    the 


Fig.  91. — I,  Hypophysis  ;   2,  in  median  section  ; 
3,  in  horizontal  section.      (Schwalbe. ) 


a.  Anterior  lobe. 

b.  Posterior  lobe. 
cm.  Corpus  mamillare. 

/.  Tuber  cinereum. 

ch.  Optic  chiasma  in  section. 


ro-  Optic  recess  of  the  third  ventricle. 
o.  Optic  ner\-e. 

a! .  Infundibulum  with  projection  from 
anterior  lobe  upwards  anterior 
to  it. 


internal  maxillary  or  from  the  middle  meningeal.  Each 
enters  the  cranium  through  the  corresponding  foramen  ovale, 
but  it  should  not  be  looked  for  at  the  present  stage,  as  it 
is  best  examined  along  with  the  semilunar  (O.T.  Gasserian) 
ganglion  and  the  three  divisions  of  the  trigeminal  nerve. 

The  mejiingeal  branches  fro7n  the  ascending  pharyngeal  arteries 
are  the  terminal  twigs  of  those  vessels.  They  enter  the 
cranium  through  the  lacerate  and  jugular  foramina,  and 
through  the  hypoglossal  canal  (O.T.  anterior  condyloid 
foramen).  The  branch  which  passes  through  the  jugular 
foramen  is  the  largest. 

The  ?nemngeal  bra?iches  of  the  occipital  and  vertebral  arteries 
are  small,  and  are  distributed  in  the  posterior  cranial  fossa. 
The  former  enter  through  the  jugular,  mastoid,  and  parietal 
foramina,  the  latter  through  the  foramen  magnum. 


2  22  HEAD  AND  NECK 

The  meningeal  veins  may  be  regarded  as  being  arranged  in 
two  sets :  one  set  consists  of  small  channels  which  pour  their 
blood  into  the  blood  sinuses ;  the  other  set  is  composed  of 
veins  which  accompany  the  meningeal  arteries  and  carry 
their  blood  to  venous  trunks  on  the  exterior  of  the  cranium. 

Hypophysis  Cerebri  (O.T.  Pituitary  Body)  (Fig.  91). — 
The  over-hanging  margin  of  the  diaphragma  sellse  should  be 
cut  away  and  the  hypophysis  carefully  dislodged  from  the 
fossa  hypophyseos  (O.T.  pituitary  fossa)  of  the  sphenoid  bone. 
It  is  an.  oval  structure,  slightly  flattened  from  above  down- 
wards, and  with  its  long  axis  directed  transversely.  It  consists 
of  a  large  anterior  lobe,  and  a  smaller  posterior  lobe.  The 
anterior  lobe  is  hollowed  out  posteriorly  so  as  to  form  a 
concavity  for  the  lodgment  of  the  posterior  lobe.  If  a  sagittal 
section  is  made  through  the  body,  the  line  of  separation 
between  the  two  lobes  is  seen  very  distinctly.  The  infundi- 
bulum,  which  connects  the  hypophysis  with  the  tuber  cinereum 
of  the  brain,  is  attached  to  the  posterior  lobe  only  (Fig.  91,  i). 
Thus,  even  in  the  adult,  there  is  a  clue  to  the  different  modes 
of  development  of  the  two  lobes.  The  posterior  lobe  is  derived 
from  the  brain,  whilst  the  anterior  lobe  is  an  off-shoot  from 
the  primitive  buccal  cavity. 

When  the  inspection  of  the  interior  of  the  cranium  is  completed  the 
dissectors  must  fill  the  cranial  cavity  with  tow  steeped  in  preservative  solu- 
tion ;  replace  the  skull-cap  in  position  and  retain  it  by  bringing  the  scalp  flaps 
over  it,  and  stitching  them  accurately  together.  The  brain  must  be  put  in 
a  jar  in  a  5  per  cent  solution  of  formalin  and  placed  aside  till  the  dissection 
of  the  remaining  parts  of  the  head  and  neck  is  finished. 


THE  ANTERIOR  PART  OF  THE  NECK. 

After  the  skull-cap  has  been  replaced  and  the  scalp  has 
been  stitched  over  it  let  the  head  hang  down  over  the  end  of 
the  table,  pull  the  chin  as  far  from  the  sternum  as  possible 
and  fix  it  in  position  with  hooks.  Then  examine  the  region  of 
the  front  of  the  neck.  It  is  a  large  triangular  area,  bounded 
laterally  by  the  anterior  borders  of  the  sterno-mastoid  muscles, 
above  by  the  lower  border  of  the  mandible,  and  below  by  the 
middle  part  of  the  upper  border  of  the  manubrium  sterni ;  and 
it  is  divided  by  the  median  plane  into  two  smaller  subsidiary 
triangles,  the  anterior  triangles  of  the  neck,  each  of  which  is 
bounded  above  by  the  mandible,  posteriorly  by  the  sterno- 


THE  ANTERIOR  PART  OF  THE  NECK       223 

mastoid,  and  anteriorly  by  the  median  plane.  Pass  the  index 
finger  from  the  chin  to  the  sternum  along  the  median  line  and 
locate  in  sequence  the  body  of  the  hyoid  bone,  the  angular 
anterior  border  of  the  thyreoid  cartilage,  the  rounded  arch  of 
the  cricoid  cartilage  and  the  rings  of  the  trachea.  The  latter 
are  partly  masked  by  the  isthmus  of  the  thyreoid  gland. 
Place  the  thumb  and  the  forefinger  on  the  body  of  the  hyoid 
bone  and  carry  them  posteriorly,  one  on  each  side,  along  its 
great  cornua.  Note  that  the  posterior  ends  of  the  cornua  lie 
immediately  in  front  of  the  anterior  borders  of  the  sterno- 
mastoid  muscles.  Above  the  body  of  the  hyoid  bone  Hes  the 
submental  triangle  roofed  in  by  the  mylo-hyoid  muscles,  which 
form  the  diaphragm  of  the  mouth  ;  and  above  each  great  cornu 
is  the  corresponding  suhnaxillary  region.  Between  the  body 
of  the  hyoid  bone  and  the  upper  margin  of  the  thyreoid 
cartilage  is  the  thyreo-hyoid  space,  bounded  posteriorly  by  the 
middle  part  of  the  thyreo-hyoid  membrane,  which  lies  anterior 
to  the  upper  part  of  the  pharynx  and  the  middle  of  the 
epiglottis  (Fig.  159).  Trace  the  upper  border  of  the  thyreoid 
cartilage  posteriorly  and  note  that  it  terminates  on  each 
side  in  a  pointed  projection,  the  superior  cornu,  which  lies 
immediately  in  front  of  the  anterior  border  of  the  sterno- 
mastoid.  Between  the  lower  margin  of  the  thyreoid  cartilage 
and  the  upper  border  of  the  cricoid  cartilage  lies  the  crico- 
thyreoid  ligament,  forming  part  of  the  anterior  wall  of  the 
lower  portion  of  the  larynx. 

The  dissectors  should  make  themselves  thoroughly  familiar 
with  the  landmarks  mentioned  above,  both  on  their  own  necks 
and  on  the  necks  of  their  friends,  and  they  should  note  that 
whilst  in  the  dead  subject  there  may  be  some  difficulty  in 
palpating  the  isthmus  of  the  thyreoid  gland,  as  it  crosses 
anterior  to  the  second,  third,  and  fourth  rings  of  the  trachea, 
they  will  have  no  difficulty  in  locating  the  small  soft  cushion- 
like mass  in  the  fiving  subject. 

Dissection. — The  skin  was  cut  along  the  lower  border  of  the  mandible 
at  the  commencement  of  the  dissection  of  the  face  ;  now,  make  a  median 
incision  through  it  from  the  chin  to  the  sternum  and  turn  the  triangular 
flap,  thus  marked  out,  posteriorly  and  laterally,  to  a  short  distance  beyond 
the  anterior  margin  of  the  sterno-mastoid.  When  this  is  done  the  super- 
ficial fascia  covering  the  anterior  triangle  on  each  side  will  be  exposed  ;  it 
is  thickest  and  most  laden  with  fat  in  the  submental  region.  In  the  upper 
part  of  it  lie  the  fibres  of  the '  platysma,  running  upwards  and  anteriorly 
towards  the  mandible.  The  anterior  fibres  of  the  muscle  gain  attachment 
to  the  anterior  part  of  the  lower  border  of  the  mandible,  and  some  decussate 


2  24  HEAD  AND  NECK 

with  those  of  the  opposite  side  beneath  the  chin.  The  posterior  fibres  ascend 
into  the  face,  where  they  have  aheady  been  followed  to  their  connection 
with  the  risorius  and  the  orbicularis  oris  (p.  126).  Cut  through  the  platysma 
along  the  anterior  border  of  the  sterno-mastoid  and  turn  it  upwards,  dividing 
the  twigs  of  the  cervical  branch  of  the  facial  nerve  which  supply  it.  Secure  the 
two  terminal  branches  of  the  nervus  cutaneus  colli  (O.T.  transverse  cervical 
nerve),  crossing  the  middle  of  the  sterno-mastoid,  and  the  cervical  branch 
of  the  facial  nerve  below  the  angle  of  the  mandible.  Trace  the  nerves 
anteriorly,  and  note  the  union  between  the  upper  branch  of  the  nervus 
cutaneus  colli  and  the  cervical  branch  of  the  facial.  In  the  superficial 
fascia  of  the  submental  region  and  the  anterior  part  of  the  submaxillary 
region  secure  the  tributaries  of  the  anterior  jugular  vein  ;  trace  them  down- 
wards to  the  trunk  of  the  vein  and  follow  the  trunk  to  the  point  where  it 
pierces  the  deep  fascia  ;  then  remove  the  superficial  fascia  and  expose  the 
deep  fascia  of  the  anterior  region.  Note  that  the  deep  fascia  extends  in  a 
continuous  layer  from  the  mandible  to  the  sternum  and  from  the  sterno- 
mastoid  of  one  side  to  that  of  the  other  side.  Note,  further,  that  it  is 
attached  to  the  body  and  the  great  cornua  of  the  hyoid  bone.  The  latter 
attachment  separates  the  infra-hyoid  muscles,  which  lie  in  the  lower  part  of 
the  neck,  from  the  supra-hyoid  muscles,  which  are  situated  in  the  region  of 
the  floor  of  the  mouth. 

The  dissectors  will  remember  that  in  the  course  of  the  dissection  of  the 
posterior  triangle  they  met  with  several  layers  of  the  deep  fascia.  A  similar 
division  into  layers  exists  in  the  anterior  region,  and  the  opportunity  should 
be  taken,  whilst  the  fascia  is  still  uninjured,  to  demonstrate  certain  of  the 
layers  and  the  presence  of  the  spaces  between  them. 

The  Suprasternal  Space. — Make  a  transverse  incision 
through  the  deep  fascia,  immediately  above  the  sternum,  and 
two  vertical  incisions,  one  along  the  anterior  border  of  each 
sterno-mastoid  muscle.  Carry  the  latter  incisions  upwards 
for  about  one  and  a  half  inches,  and  turn  the  flap  of  fascia 
marked  out  upwards.  The  space  opened  into  by  the  reflection 
of  the  first  layer  of  deep  fascia  of  the  lower  part  of  the  neck 
is  the  suprasternal  space  (Burns).  Remove  the  areolar  tissue 
which  fifls  it,  find  the  lower  parts  of  the  anterior  jugular 
veins  and  the  transverse  anastomosis  between  them,  and 
expose  the  second  layer  of  deep  fascia,  which  forms  the 
posterior  boundary  of  the  space  and  covers  and  binds  together 
the  infra-hyoid  muscles  of  opposite  sides.  Pass  the  handle  of 
the  scalpel  downwards  along  the  posterior  wall  of  the  space, 
and  note  that  it  terminates,  a  short  distance  below  the 
upper  border  of  the  sternum,  where  the  second  layer  of  fascia 
is  attached  to  the  posterior  surface  of  the  manubrium, 
immediately  above  the  origins  of  the  infra-hyoid  muscles.  If 
the  handle  of  the  knife  is  passed  laterally  along  the  posterior 
wall  of  the  space,  it  will  pass  deep  to  the  sterno-mastoid  into 
the  posterior  triangle  (see  p.  145),  and  if  it  is  pushed  upwards 
it  will  be  stopped  by  the  union  of  the  first  and  second  layers 


THE  ANTERIOR  PART  OF  THE  NECK        225 

of  the  deep  fascia  about  half-way  between  the  sternum  and 
the  thyreoid  cartilage.  The  attachments  of  the  second  layer 
of  deep  fascia  of  the  lower  part  of  the  neck  may  be  summarised 
as  follows.  It  is  attached  below  to  the  posterior  surface  of 
the  manubrium  sterni  and  to  the  posterior  border  of  the 
clavicle,  to  which  it  binds  the  posterior  belly  of  the  omo-hyoid 
(p.  145).  Above,  it  fuses  with  the  more  superficial  layer,  along 
an  oblique  line  which  ascends  from  the  level  of  the  coracoid 
process  to  the  level  of  the  upper  end  of  the  trachea.  Above 
that  level  it  forms,  with  the  superficial  layer,  a  common  lamella, 
which  ascends  on  the  infra-hyoid  muscles  to  gain  attachment 
to  the  body  and  great  cornu  of  the  hyoid  bone.  The  space 
between  the  two  layers  contains,  in  the  region  of  the  anterior 
triangle,  the  lower  parts  of  the  anterior  jugular  veins,  the 
anastomosis  between  them,  and  the  areolar  tissue  in  which 
they  are  embedded.  In  the  posterior  triangle  its  contents  are 
the  lower  end  of  the  external  jugular  vein,  the  terminations  of 
the  transverse  cervical  and  transverse  scapular  veins,  the 
transverse  scapular  artery,  and  areolar  tissue.  Note  that  the 
anterior  jugular  vein  on  each  side  lies  superficial  to  the  deep 
fascia  in  the  upper  part  of  the  neck ;  then  it  pierces  the  first 
layer  of  deep  fascia  and  lies  between  the  two  layers,  where  it 
anastomoses  with  its  fellow  of  the  opposite  side  ;  finally  it  turns 
laterally  deep  to  the  sterno-mastoid,  and  terminates  in  the 
external  jugular  vein  at  the  anterior  boundary  of  the  sub- 
clavian part  of  the  posterior  triangle. 

Dissection. — Make  two  incisions  through  the  deep  fascia  of  the  upper 
part  of  the  anterior  triangle,  one  along  the  lower  border  of  the  mandible 
from  the  angle  to  half  an  inch  from  the  chin,  and  a  second  at  right  angles 
to  the  first,  from  its  middle  to  the  great  cornu  of  the  hyoid  bone.  Whilst 
making  the  horizontal  incision  avoid  injuring  the  external  maxillary  artery 
(O.T.  facial)  and  the  anterior  facial  vein,  which  pierce  the  deep  fascia  at 
the  level  of  the  anterior  border  of  the  masseter.  Reflect  the  two  triangular 
flaps  of  fascia  marked  out  by  the  incisions  and  expose  the  lower  surface  of 
the  submaxillary  gland,' the  submaxillary  lymph  glands,  the  anterior  and 
posterior  bellies  of  the  digastric  muscle,  the  lower  part  of  the  stylo-hyoid 
muscle,  and  a  further  part  of  the  anterior  facial  vein. 

The  majority  of  the  submaxillary  lymph  glands  lie  along 
the  lower  border  of  the  mandible  on  the  superficial  surface  of 
the  submaxillary  gland.  The  anterior  facial  vein  crosses  the 
posterior  part  of  the  submaxillary  gland  superficially.  The 
external  maxillary  artery  dips  deeply  between  the  lower  border 
of  the  mandible  and  the  submaxillary  gland.  The  posterior 
VOL.  II — 15 


2  26  HEAD  AND  NECK 

and  lower  part  of  the  submaxillary  gland  usually  overlaps  the 
stylo-hyoid  and  the  posterior  belly  of  the  digastric  muscles, 
and  not  infrequently  it  overlaps  the  great  cornu  of  the  hyoid 
bone  also.  Its  anterior  border  may  overlap  the  anterior 
belly  of  the  digastric.  Raise  the  lower  border  of  the  gland 
and  expose  another  layer  of  deep  fascia  covering  the  muscles 
which  lie  deep  to  it.  Place  the  handle  of  the  knife  on  this 
fascia  and  push  it  gently  upwards.  Note  that  it  passes 
upwards  to  the  level  of  the  mylo-hyoid  line  on  the  inner  surface 
of  the  mandible,  to  which  the  mylo-hyoid  muscle  is  attached. 
The  fascial  sheath  in  which  the  submaxillary  gland  is  enclosed 
consists,  therefore,  of  a  superficial  layer  of  deep  fascia  which 
extends  from  the  great  cornu  of  the  hyoid  bone  to  the  lower 
border  of  the  mandible,  and  a  deeper  layer  which  passes  from 
the  great  cornu  of  the  hyoid  to  the  mylo-hyoid  line  of  the 
mandible.  The  two  layers  blend  in  front  of  the  anterior 
belly  of  the  digastric,  and  posteriorly  they  unite,  behind  the 
posterior  belly  of  the  digastric,  with  the  connective  tissue  in 
which  the  carotid  vessels  are  embedded. 

Dissection. — Remove  the  deep  fascia  in  the  region  of  the  anterior 
triangle  and  expose  the  divisions  and  the  contents  of  the  triangle. 

The  Divisions  of  the  Anterior  Triangle. — After  the  deep 
fascia  is  removed,  the  dissector  will  recognise  that  each 
anterior  triangle  may  be  divided  into  three  subsidiary  areas 
which  are  called  the  digastric,  the  carotid,  and  the  muscular 
triangles,  by  means  of  the  two  beUies  of  the  digastric  muscle 
and  the  anterior  belly  of  the  omo-hyoid  muscle. 

The  digastric  triangle  is  bounded  by  the  two  bellies  of  the 
digastric  muscle  and  the  lower  border  of  the  mandible. 

The  boundaries  of  the  carotid  triangle  are,  above  and  in 
front,  the  posterior  belly  of  the  digastric  \  below  and  in  front, 
the  anterior  belly  of  the  omo-hyoid ;  and,  behind,  the  anterior 
border  of  the  sterno-mastoid. 

The  muscular  triangle  is  bounded,  above  and  behind,  by 
the  anterior  belly  of  the  omo-hyoid ;  below  and  behind, 
by  the  anterior  border  of  the  sterno-mastoid ;  and  in  front, 
by  the  middle  line  of  the  neck. 

An  additional  triangle  common  to  the  two  sides  lies  between  the  hyoid 
bone  below,  the  two  anterior  bellies  of  the  digastrics  laterally,  and  the 
mandible  above.     This  is  called  the  submental  triangle. 

The  Middle  Line  of  the  Neck. — Before  commencing  the 


THE  ANTERIOR  PART  OF  THE  NECK       227 

dissection  of  the  contents  of  the  subsidiary  parts  of  the 
anterior  triangle  the  dissectors  of  both  sides  should,  together, 
study  the  structures  which  lie  in  the  middle  line  of  the  neck 
and  immediately  to  either  side  of  it ;  for  this  region  is  of  the 
highest  importance  to  the  surgeon.  The  area  is  divided  by 
the  hyoid  bone  into  supra-hyoid  and  infra-hyoid  portions. 

In  the  supra-hyoid  part  lie  structures  which  are  concerned 
in  the  construction  of  the  floor  of  the  mouth.     The  dissector 


Occipital  triangle. 


Subclavian  triangle 


Digastric  triangle 
Carotid  triangle 

— i -Muscular  triangle 


(^m{[\m\i%y\^ 


Fig.  92. — Diagram  to  show  the  Boundaries  of  the  Triangles  of  the  Neck. 

will  have  noticed  already  that  the  fatty  superficial  fascia  is 
more  fully  developed  here  than  elsewhere  in  the  neck,  and 
that  the  anterior  margins  of  the  two  platysma  muscles  meet 
and  decussate  in  the  median  plane,  for  about  half  an  inch 
or  so,  below  the  chin.  The  anterior  belhes  of  the  two 
digastric  muscles  are  attached  to  the  mandible,  one  on  either 
side  of  the  symphysis.  From  this  they  descend  towards  the 
hyoid  bone,  and  diverge  slightly  from  each  other  so  as  to 
leave  a  narrow  triangular  space,  the  submental  triangle^  be- 
tween them  (Fig.  93).  The  floor  of  this  space  is  formed  by 
the  anterior  portions  of  the  two  mylo-hyoid  muscles,  whilst 
II — 15  a 


228 


HEAD  AND  NECK 


bisecting  tiie  floor  of  the  triangle,  in  the  median  plane,  is  the 
fibrous  raphe  into  which  these  muscles  are  inserted.  Not 
infrequently  the  medial  margins  of  the  digastric  muscles  send 
decussating  fibres  across  the  interval.  Within  the  submental 
triangle  are  the  submental  glands^  which   receive  lymph  from 


Anterior  facial  vein 
Mylo-hyoid 
muscle 
Common  facial 
vein- 
Lingual  vein. 
Small  occipital  N.. 
Great  auricular  N.- 
Nervus 
cutaneus  colli 
I  n  ternal  j  ugular  vein 
Descending 
cervical"""' 

nerves / 
Brachial, 
plexus 
ExternaL- 
jugular  vein 
Descendens 
hypoglossi 
Anterior 
jugular  vein 

Inferior 
thyreoid  veins 


Platysma 


External  maxillary 
artery 

Parotid  gland 
Submental  lymph 
gland 
Submaxillary  gland 

Sterno-mastoid  artery 
Ext.  carotid  artery 

Sup.  thyreoid  artery 
Common  carotid 
artery 
Lymph  gland 

Thyreo-glossal  duct 
Omo-hyoid 

Crico-thyreoid 

Sterno-hyoid 

Isthmus  of  thyreoid 
gland 


Sterno-thyreoid 


Fig.  93. — Dissection  of  the  Front  of  the  Neck. 

has  been  removed. 


The  Right  Sterno-mastoid 


the  median  part  of  the  lower  lip  and  chin  and  the  anterior 
part  of  the  tongue. 

In  the  median  area  of  the  infra-hyoid  part  there  is  a 
narrow  intermuscular  interval,  bounded  on  each  side,  above, 
by  the  medial  margins  of  the  sterno-hyoid  muscles,  and  to  a 
smaller  extent,  below,  by  the  medial  margins  of  the  sterno- 
thyreoid  muscles  (Fig.  93);  more  laterally  lie  the  anterior  bellies 


THE  ANTERIOR  PART  OF  THE  NECK   229 

of  the  omo-hyoid  muscles.  In  this  median  intermuscular 
interval  the  following  structures  will  be  found  :  (i)  the  median 
part  of  the  thyreo-hyoid  membrane ;  (2)  the  anterior  border 
of  the  thyreoid  cartilage  with  the  projecting  prominentia 
laryngea  (O.T.  pomum  adami)  at  its  upper  end;  (3)  the 
arch  of  the  cricoid  cartilage ;  (4)  the  crico-thyreoid  ligament 
with  the  anastomosis  between  the  crico-thyreoid  arteries,  and 
the  anterior  ends  of  the  crico-thyreoid  muscles;  (5)  the  first 
ring  of  the  trachea  with  the  anastomosis  between  the  medial 
terminal  branches  of  the  superior  thyreoid  arteries ;  (6)  the 
isthmus  of  the  thyreoid  gland;  (7)  the  inferior  thyreoid  veins, 
and  (8)  the  lower  cervical  rings  of  the  trachea.  Occasionally 
the  third  or  middle  lobe  of  the  thyreoid  gland  and  the 
levator  glandulae  thyreoidea,  or  one  or  other  of  them,  is  found 
extending  upwards  from  the  isthmus  of  the  thyreoid  gland. 
When  it  is  present  the  middle  lobe  either  terminates  above 
in  a  pointed  extremity  or  becomes  continuous  with  a  fibrous 
cord,  the  remains  of  the  thyreo -glossal  duct,  which  disappears 
posterior  to  the  hyoid  bone.  The  levator  extends  from  the 
isthmus  or  from  the  third  lobe,  and  is  attached  above  to  the 
lower  border  of  the  hyoid  bone. 

Dissection. — To  display  these  structures  fully  the  fascia  which  covers  and 
binds  together  the  infra-hyoid  muscles  of  opposite  sides  must  be  removed. 
When  this  has  been  done  the  anterior  part  of  the  thyreoid  cartilage  will  be 
exposed,  and,  above  it,  in  the  thyreo-hyoid  interval,  lies  some  loose  areolar 
tissue.  If  an  incision,  directed  upwards  and  posteriorly,  is  made  into  this 
tissue,  behind  the  lower  border  of  the  hyoid  bone,  the  infra-hyoid  bursa 
will  be  opened,  and  when  this  and  the  areolar  tissue  are  removed,  the 
thyreo-hyoid  membrane  will  be  exposed.  Note  that  the  membrane  extends 
from  the  upper  border  of  the  thyreoid  cartilage  posterior  to  the  body  of  the 
hyoid  bone  to  its  upper  border.  When  the  areolar  tissue  in  the  lower  part 
of  the  intermuscular  interval  is  removed  the  inferior  thyreoid  veins  will  be 
displayed  ;  they  disappear,  below,  behind  the  sternum  where  they  join  the 
innominate  veins.  Occasionally  also  a  small  unpaired  artery,  the  thyreoidea 
ii?ia,  will  be  found  ascending,  in  the  median  plane,  to  the  isthmus  of  the 
thyreoid  gland.  Behind  the  inferior  thyreoid  veins  lies  another  layer  of 
deep  cervical  fascia,  the  pretracheal  layer.  It  covers  the  front  of  the 
trachea,  envelops  the  isthmus  of  the  thyreoid  gland,  and  is  attached  above 
to  the  lower  border  of  the  thyreoid  cartilage.  The  part  which  extends 
from  the  isthmus  of  the  thyreoid  gland  to  the  thyreoid  cartilage  acts  as  a 
suspensory  ligament  of  the  isthmus.  The  dissectors  will  find  that,  so  long 
as  the  attachments  of  this  part  of  the  pretracheal  fascia  are  not  interfered 
with,  they  cannot  displace  the  isthmus  of  the  thyreoid  gland  downwards. 
On  the  other  hand,  if  they  cut  through  the  attachment  of  the  fascia  to  the 
thyreoid  cartilage,  introduce  the  handle  of  the  knife  through  the  incision, 
and  press  downwards,  they  will  be  able  to  displace  the  isthmus  of  the 
thyreoid  gland  to  a  lower  level  and  expose  the  upper  rings  of  the  trachea. 
At  the  root  of  the  neck  the  pretracheal  fascia  descends  into  the  thorax, 
II — 15  h 


2  30  HEAD  AND  NECK 

along  the  anterior  surface  of  the  trachea,  and  it  blends  below  with  the 
fibrous  pericardium. 

Remove  the  pretracheal  fascia  from  the  region  of  the  intermuscular 
interval,  first  above  and  then  below  the  isthmus  of  the  thyreoid  gland.  As 
the  fascia  is  dissected  away  the  following  structures  will  be  displayed. 
Immediately  below  the  thyreoid  cartilage  is  the  crico-thyreoid  ligament, 
overlapped  on  each  side  by  the  anterior  part  of  the  crico-thyreoid  muscle. 
Crossing  anterior  to  the  ligament,  transversely,  is  the  anastomosis 
between  the  crico-thyreoid  branches  of  the  superior  thyreoid  arteries. 
It  lies  nearer  the  lower  than  the  upper  border  of  the  ligament.  Below 
the  crico-thyreoid  ligament  is  the  convex  anterior  part  of  the  cricoid 
cartilage ;  then  follows  the  crico-tracheal  ligament,  uniting  the  cricoid 
cartilage  to  the  first  ring  of  the  trachea.  The  isthmus  of  the  thyreoid 
gland  lies  at  a  lower  level  opposite  the  second,  third,  and  fourth  rings  of 
the  trachea.  Along  its  upper  border  is  the  anastomosis  between  the 
medial  terminal  branches  of  the  superior  thyreoid  arteries,  and  below  it 
are  the  lower  cervical  tracheal  rings. 

The  superficial  layers  of  the  deep  fascia  must  now  be  removed  from  the 
whole  area  of  each  anterior  triangle,  and  for  this  purpose  and  for  the 
satisfactory  dissection  of  the  contents  of  the  triangles,  it  is  necessary  that 
the  head  be  turned  well  over  to  the  opposite  side  ;  therefore  the  dissectors 
must  arrange  to  work  alternately. 

Commence  with  the  digastric  triangle.  Its  boundaries  are 
the  lower  border  of  the  mandible  and  the  two  bellies  of  the 
digastric  muscle. 

Its  contents  are:  (i)  the  lower  part  of  the  submaxillary 
gland;  (2)  the  submaxillary  lymph  glands;  (3)  part  of  the 
external  maxillary  artery ;  (4)  part  of  the  anterior  facial  vein  ; 
(5)  the  mylo-hyoid  nerve;  (6)  the  mylo-hyoid  artery;  (7)  a 
small  part  of  the  hypoglossal  nerve ;  (8)  a  small  part  of  the 
lingual  vein. 

Dissection. — Remove  the  deep  fascia  which  was  previously  turned  aside 
(p.  225)  and  clean  the  submaxillary  lymph  glands.  Most  of  these  glands 
lie  immediately  below  the  mandible  in  the  angle  between  it  and  the  sub- 
maxillary gland,  but  some  may  be  found  on  the  superficial  surface  of  the 
gland.  Turn  the  gland  upwards  and  fix  it  with  hooks ;  then  secure  the 
mylo-hyoid  nerve  and  artery  as  they  enter  the  posterior  border  of  the 
anterior  belly  of  the  digastric  about  the  middle  of  its  length.  Define  the 
band  of  fascia  which  surrounds  the  intermediate  tendon  of  the  digastric  and 
binds  it  to  the  great  cornu  of  the  hyoid  bone.  Note  that  the  tendon  is  em- 
braced by  the  cleft  lower  end  of  the  stylo-hyoid  muscle.  Clean  the  posterior 
belly  of  the  digastric  and  the  stylo-hyoid  muscle  which  descends  along  its 
anterior  border.  Note  that  the  posterior  belly  of  the  digastric  and  the 
stylo-hyoid  disappear,  postero-superiorly,  under  cover  of  the  angle  of  the 
mandible.  Clean  the  anterior  belly  of  the  digastric,  and  then  examine 
the  floor  or  medial  boundary  of  the  triangle.  Immediately  behind  the 
anterior  belly  of  the  digastric  it  is  formed  by  the  posterior  fibres  of  the 
mylo-hyoid  muscle  ;  and  more  posteriorly  and  on  a  deeper  plane  it  is 
formed  by  the  hyoglossus. 

Clean  the  portion  of  the  mylo-hyoid  which  is  exposed  and,  at  its 
posterior  border,  immediately  above  the  great  cornu  of  the  hyoid  bone, 


THE  ANTERIOR  PART  OF  THE  NECK      231 

secure  the  hypoglossal  nerve  and  the  lingual  vein,  the  vein  lying  below 
the  nerve.  Displace  the  lingual  vein  and  the  hypoglossal  nerve  upwards  ; 
cut  through  the  fibres  of  the  hyoglossus,  immediately  above  and  parallel 
with  the  great  cornu,  and  display  the  lingual  artery,  which  in  this  position 
lies  immediately  above  the  great  cornu,  parallel  with  the  lingual  vein  but 
separated  from  it  by  the  hyoglossus  muscle. 

All  the  structures  which  have  been  mentioned  above  will  be  met  with 
in  the  dissection  of  other  regions,  when  a  full  account  of  them  will  be  given. 

Turn  next  to  the  carotid  triangle,  so  called  because  it 
contains  parts  of  the  common,  internal,  and  external  carotid 
arteries.  It  is  bounded  posteriorly  by  the  anterior  border  of 
the  sterno-mastoid ;  above  and  anteriorly  by  the  posterior 
belly  of  the  digastric ;  and  below  and  anteriorly  by  the  anterior 
belly  of  the  omo-hyoid. 

Dissection. — Trace  the  anterior  facial  vein  from  the  digastric  triangle 
across  the  superficial  surface  of  the  posterior  belly  of  the  digastric  to  its 
posterior  border,  where  it  unites  with  the  posterior  facial  vein,  which  is 
descending  from  under  cover  of  the  lower  end  of  the  parotid  gland.  The 
trunk  formed  by  the  union  of  the  anterior  and  posterior  facial  veins  is  the 
common  facial  vein.  Trace  the  common  facial  vein  downwards  and 
posteriorly  to  its  union  with  the  internal  jugular  vein,  at  or  under  cover 
of  the  anterior  border  of  the  sterno-mastoid.  Remove  the  deep  fascia 
and  the  areolar  tissue,  and  the  lymph  glands  which  lie  in  the  angle  between 
the  posterior  belly  of  the  digastric  and  the  anterior  border  of  the  sterno- 
mastoid,  below  the  lower  end  of  the  parotid  gland  ;  secure  the  lingual 
vein,  which  passes  backwards  from  the  tip  of  the  great  cornu  of  the  hyoid 
bone  to  join  the  internal  jugular  vein  ;  and  the  hypoglossal  nerve  as  it 
crosses  anteriorly  at  a  higher  level,  superficial  to  the  internal  and  external 
carotid  arteries.  As  the  nerve  turns  anteriorly  across  the  large  arteries  it 
is  itself  crossed,  superficially,  by  the  sterno-mastoid  branch  of  the  occipital 
artery,  and  it  gives  off  its  descending  branch.  Trace  the  descending 
branch  downwards,  in  the  fascia  which  lies  superficial  to  the  lower  part 
of  the  internal  and  the  upper  part  of  the  common  carotid  arteries,  to 
the  point  where  it  disappears  under  cover  of  the  anterior  belly  of  the 
omo-hyoid,  avoiding  injuiy  to  the  lingual,  common  facial,  and  superior 
thyreoid  veins  ;  ^  and  secure  the  communicating  branch,  from  the  second 
and  third  cervical  nerves,  which  joins  its  posterior  aspect.  The  latter 
nerve  may  cross  either  superficial  or  deep  to  the  internal  jugular  vein. 
Return  to  the  hypoglossal  nerve  at  the  point  where  it  gives  oft'  its  descending 
branch,  and  trace  it  anteriorly  to  the  upper  aspect  of  the  posterior  end 
of  the  great  cornu  of  the  hyoid  bone,  where  it  gives  off  the  branch  of 
supply  to  the  thyreo-hyoid  muscle.  Trace  the  branch  into  that  muscle 
below  the  level  of  the  great  cornu,  then  follow  the  trunk  of  the  hypoglossal 
anteriorly  to  the  digastric  triangle.  Note  that  as  it  runs  anteriorly  it 
passes  deep  to  the  posterior  belly  of  the  digastric  and  the  stylo-hyoid 
muscle,  and  superficial  to  the  hyoglossus,  which  ascends  to  the  tongue  from 

^  The  lingual  vein  may  join  the  common  facial  vein,  in  which  case  the 
latter  usually  enters  the  internal  jugular  opposite  the  interval  between  the 
hyoid  bone  and  the  thyreoid  cartilage,  as  in  the  specimen  depicted  in  Fig.  93. 
The  superior  thyreoid  vein  joins  the  internal  jugular  or  the  common  facial 
vein  opposite  the  thyreo-hyoid  interval. 
II — 15  c 


232  HEAD  AND  NECK 

the  upper  border  of  the  great  cornu.  Remove  the  fascial  sheath  from  the 
superficial  surfaces  of  the  lower  parts  of  the  internal  and  external  carotid 
arteries,  and  from  the  upper  part  of  the  common  carotid  artery.  Note  that 
the  latter  divides  into  the  two  former  at  the  level  of  the  upper  border 
of  the  thyreoid  cartilage,  and  that  the  external  carotid  is  at  first  medial 
and  anterior  to  the  internal  carotid. 

Five  branches  may  spring  from  the  external  carotid  in  the  carotid 
triangle,  three  from  its  anterior  surface  :  the  superior  thyreoid,  the  lingual 
and  the  external  maxillary  ;  one  from  its  medial  surface,  the  ascending 
pharyngeal ;  and  one  from  its  posterior  surface,  the  occipital ;  but  not  un- 
commonly the  occipital  and  the  external  maxillary  arise  beyond  the  limits 
of  the  carotid  triangle  under  cover  of  the  posterior  belly  of  the  digastric. 
The  superior  thyreoid  springs  from  the  front  of  the  lower  part  of  the  ex- 
ternal carotid  below  the  level  of  the  great  cornu  of  the  hyoid  and  runs 
downwards  to  the  lower  angle  of  the  carotid  triangle,  where  it  disappears 
under  cover  of  the  anterior  belly  of  the  omo-hyoid.  The  lingual  arises 
immediately  above  the  level  of  the  tip  of  the  great  cornu.  It  runs  an- 
teriorly above  the  level  of  the  cornu,  forming  a  loop,  convex  upwards, 
which  lies  deep  to  the  hypoglossal  nerve  ;  and  it  disappears  under  cover 
of  the  posterior  border  of  the  hyoglossus  muscle.  The  ascending  pharyngeal 
branch,  which  springs  from  the  medial  surface  of  the  lower  end  of  the  ex- 
ternal carotid,  ascends  on  a  deeper  plane,  between  the  external  and  in- 
ternal carotids  and  the  wall  of  the  pharynx,  and  will  be  followed  at  a  later 
stage  of  the  dissection.  The  external  maxillary  and  the  occipital  arise 
immediately  below  the  posterior  belly  of  the  digastric  and  almost  at 
once  disappear  under  cover  of  the  muscle ;  not  uncommonly  they 
arise  under  cover  of  its  lower  border.  Before  proceeding  to  clean  the 
branches  of  the  external  carotid  secure  the  internal  and  external  laryngeal 
branches  of  the  superior  laryngeal  branch  of  the  vagus  nerve.  The  internal 
branch  will  be  found  in  the  posterior  part  of  the  thyreo-hyoid  interval  below 
the  great  cornu  of  the  hyoid  bone  and  behind  the  posterior  border  of  the 
thyreo-hyoid  muscle,  beneath  which  it  disappears.  It  is  accompanied  by 
the  laryngeal  branch  of  the  superior  thyreoid  artery.  The  external  branch 
is  more  difficult  to  find  ;  but,  if  the  superior  thyreoid  artery  and  the  upper 
part  of  the  common  carotid  are  displaced  posteriorly,  the  nerve  will  be 
found,  lying  deep  to  them,  in  the  fascia  which  covers  the  anterior  part  of  the 
inferior  constrictor  muscle.  Remove  the  fascia  from  the  surface  of  the  in- 
ternal jugular  vein,  which  overlaps  the  posterior  borders  of  the  common 
and  internal  carotid  arteries.  Dissect  in  the  interval  between  the  vein  and 
the  arteries  and  secure  the  vagus  nerve,  which  lies  deeply.  Remove  the 
remains  of  the  fascia  from  the  carotid  arteries  and  the  internal  jugular  vein, 
but  avoid  injury  to  the  hypoglossal  nerve  and  its  branches  ;  and  note  the 
presence  of  the  upper  deep  cervical  lymph  glands  which  lie  on  the  superficial 
surfaces  of  the  great  arteries  and  the  internal  jugular  vein.  The  glands  are 
sometimes  very  large,  and  the  dissectors  should  remember  that  they  receive 
lymph  from  the  face,  the  mouth  and  tongue,  the  posterior  part  of  the  nose 
and  the  upper  part  of  the  pharynx.  After  the  large  vessels  are  cleaned, 
remove  the  fascia  from  the  branches  of  the  external  carotid  artery  and  the 
twigs  they  give  off,  so  far  as  they  lie  in  the  region  of  the  carotid  triangle. 
Commence  with  the  superior  thyreoid.  Immediately  after  its  origin  it  gives 
off  a  small  infra-hyoid  branch,  then  a  laryngeal  branch  which  accompanies 
the  internal  laryngeal  branch  of  the  superior  laryngeal  nerve  ;  and,  just 
before  it  disappears  under  cover  of  the  anterior  belly  of  the  omo-hyoid,  a 
sterno-mastoid  branch  arises  from  its  posterior  border  and  runs  downwards 
and  posteriorly,  along  the  upper  border  of  the  omo-hyoid,  across  the  super- 
ficial aspect  of  the  common  carotid  artery  and  the  internal  jugular  vein. 


THE  ANTERIOR  PART  OF  THE  NECK      233 

Next,  clean  the  lingual  artery  and  note  its  small  supra-hyoid  branch.  The 
external  maxillary  artery  gives  off  no  branches  in  the  carotid  triangle,  but  a 
sterno-mastoid  branch  of  the  occipital  artery  will  usually  be  found  passing 
downwards  and  posteriorly,  superficial  to  the  loop  of  the  hypoglossal  nerve. 
Push  the  lower  border  of  the  parotid  gland  upwards,  and  immediately  under 
cover  of  it,  at  the  level  of  the  angle  of  the  mandible,  secure  the  accessory 


Semispinalis  capitis- 
Posterior  auricular  vein  ^ 


Digastric 
Nerve  to  thyreo-h3'oid 
Thyreo-hyoid 
Superior  thyreoid  artery 
Omo-hyoid  • 


Transverse 
scapular  artery 
Scalenus  anterior 
J^-Subclavian  artery 

Subclavian  vein 


Suprascapu'ar 

N-S 


Fig.  94. — The  Triangles  of  the  Neck  seen  from  the  side.  The  clavicular  head 
of  the  sterno-mastoid  muscle  was  small,  and  therefore  a  considerable  part 
of  the  scalenus  anterior  muscle  is  seen. 

nerve,  as  it  emerges  from  under  cover  of  the  posterior  belly  of  the  digastric 
and  crosses  superficial  to  the  internal  jugular  vein.  It  is  sometimes  accom- 
panied by  an  additional  branch  to  the  sterno-mastoid  from  the  occipital 
artery. 

The  floor  or  medial  boundary  of  the  carotid  triangle   is 
formed   by  the  upper  part  of  the   thyreo-hyoid   muscle,   the 


234  HEAD  AND  NECK 

posterior  part  of  the  hyoglossus  and  the  middle  and  inferior 
constrictors  of  the  pharynx.  The  two  latter  muscles  cannot 
be  displayed  at  present,  but  the  thyreo-hyoid  is  exposed  below 
the  great  cornu  of  the  hyoid  bone,  and  part  of  the  hyoglossus 
can  be  seen  in  the  angle  between  the  great  cornu  of  the  hyoid 
and  the  lower  part  of  the  posterior  belly  of  the  digastric. 

The  Muscular  Triangle. — When  the  deep  fascia  which 
covers  the  muscular  triangle  is  removed  portions  of  the 
three  muscles  are  brought  into  view.  Postero-superiorly  is 
the  anterior  belly  of  the  omo-hyoid,  more  anteriorly  and  on 
the  same  plane  is  the  sterno-hyoid,  and  below  and  anterior  to 
the  latter,  but  on  a  deeper  plane,  is  a  small  part  of  the  sterno- 
thyreoid. 

The  muscles  mentioned  may  be  considered  to  form  the 
floor  or  medial  boundary  of  the  triangle,  and  if  this  view  is 
taken  the  structures  they  cover,  which  lie  more  deeply,  are 
under  cover  of  the  floor.  These  structures  must  now  be 
exposed. 

Dissection. — Divide  the  anterior  belly  of  the  omo-hyoid  along  the 
anterior  border  of  the  sterno-mastoid  and  turn  it  upwards  to  its  insertion 
into  the  hyoid  bone.  As  this  is  done  its  twig  of  supply  from  the  ansa  hypo- 
glossi  will  be  cut.  Divide  the  sterno-hyoid  as  low  down  as  possible  ;  turn 
it  upwards  to  its  insertion  into  the  body  of  the  hyoid  bone  and  note  its  nerve 
of  supply  from  the  loop  which  is  called  the  ansa  hypoglossi^  and  is  formed 
by  the  union  of  the  descending  branch  of  the  hypoglossal  nerve  and  the 
communicating  branch  from  the  cervical  plexus.  Secure  the  nerve  to  the 
sterno-thyreoid  from  the  ansa  hypoglossi  ;  then  remove  the  fascia  and  expose 
the  lower  part  of  the  thyreo-hyoid  muscle,  the  greater  part  of  the  sterno- 
thyreoid  and  the  anterior  part  of  the  thyreoid  cartilage.  Note  that  the 
sterno-thyreoid  is  inserted  into  an  oblique  line  on  the  outer  surface  of  the 
lamina  of  the  thyreoid  cartilage  and  that  the  thyreo-hyoid  springs  from  the 
same  line  and  is  inserted  into  the  great  cornu  of  the  hyoid  bone.  The 
crico-thyreoid  branch  of  the  superior  thyreoid  artery  may  be  found  passing 
downwards  and  anteriorly  along  the  upper  end  of  the  sterno-thyreoid 
accompanied  by  the  external  laryngeal  nerve  ;  or  the  nerve  and  the  vessel 
may  lie  deep  to  the  upper  end  of  the  muscle. 

Divide  the  sterno-thyreoid  as  low  down  as  possible  and  turn  it  upwards 
to  its  insertion  ;  remove  the  fascia  under  cover  of  it  and  expose  the  lateral 
lobe  of  the  thyreoid  gland,  and  below  it  a  small  part  of  the  side  of  the 
trachea. 

The  dissector  should  note  that  whilst  the  sterno-mastoid  remains  undis- 
turbed the  posterior  part  of  the  lateral  lobe  of  the  thyreoid  gland  and  its 
lower  extremity  are  not  exposed,  but  if  the  sterno-mastoid  is  displaced 
posteriorly  the  whole  of  the  lateral  surface  of  the  lobe  is  brought  into  view. 
The  dissector  should  note  also  that  until  the  sterno-mastoid  is  displaced 
posteriorly  only  a  small  portion  of  the  upper  end  of  the  common  carotid  and 
the  lower  parts  of  the  internal  and  external  carotid  arteries  are  visible  ; 
indeed,  the  common  carotid  may  be  entirely  concealed.  Only  a  small  part 
of  the  anterior  border  of  the  internal  jugular  vein  projects  anterior  to  the 


THE  ANTERIOR  PART  OF  THE  NECK      235 

sterno-mastoid  in  the  upper  and  posterior  angle  of  the  carotid  triangle  ;  and 
it  also  is  not  uncommonly  hidden  when  the  sterno-mastoid  is  well  developed. 
During  life,  however,  when  the  muscle  is  soft  and  pliable  the  structures 
concealed  by  it  are  readily  exposed,  for  the  muscle  is  easily  displaced 
posteriorly  after  the  fascia  has  been  divided  along  its  anterior  border.  In 
the  dissecting-room  it  is  not  possible  to  obtain  a  proper  view  of  the  course 
and  relations  of  the  common  carotid  artery  and  the  internal  jugular  vein,  or 
to  appreciate  the  relations  of  the  tirst  part  of  the  subclavian  artery  and  the 
relations  of  the  scalenus  anterior  muscle,  until  the  sterno-mastoid  has 
been  reflected.  Divide  the  external  jugular  vein  immediately  below  the 
point  where  it  is  joined  by  the  posterior  auricular  tributaiy  and  turn  it 
downwards.  Divide  the  great  auricular  nerve  at  the  level  of  the  angle  of 
the  mandible  and  turn  it  posteriorly ;  and  turn  posteriorly  the  nervus 
cutaneus  colli,  whose  two  terminal  branches  have  been  cut  already.  The 
clavicular  head  of  the  sterno-mastoid  was  cut  when  the  clavicle  was 
removed  ;  now  divide  the  sternal  head,  turn  the  muscle  upwards  towards  its 
insertion.  As  the  muscle  is  turned  upwards,  sterno-mastoid  branches  of  the 
transverse  scapular,  superior  thyreoid,  and  occipital  arteries  will  be  exposed  ; 
and  if  they  interfere  with  the  reflection  of  the  muscle  they  must  be  divided. 
Slightly  above  the  level  of  the  sterno-mastoid  branch  of  the  occipital  artery 
the  accessory  nerve  will  be  found  passing  through  the  deeper  fibres  of  the 
muscle,  and  care  must  be  taken  to  avoid  injury  to  it ;  but  it  may  be  dissected 
out  of  the  muscle  and  left  in  position  on  the  lateral  surface  of  the  internal 
jugular  vein. 

Deep  Cervical  Fascia. — When  the  sterno-mastoid  has  been 
reflected  a  deep  fascial  plane  of  the  neck  is  exposed  in  which 
lie  many  lymph  glands.  Before  carrying  the  dissection  further 
the  dissector  should  reconsider  the  arrangement  of  the  deep 
cervical  fascia.  He  has  already  seen  that  it  forms  a  complete 
sheath  enclosing  the  muscles  of  the  neck  and  the  structures 
which  lie  between  and  under  cover  of  them.  The  general 
arrangement  of  the  fascia  is  studied  best  on  transverse 
sections  of  the  neck  made  at  the  level  of  the  isthmus  of  the 
thyreoid  gland  and  a  short  distance  above  the  sternum.  At 
the  former  level  it  is  possible  to  recognise  (i)  a  superficial 
layer;  (2)  a  pretracheal  layer ;  (3)  a  prevertebral  layer;  and  (4) 
a  fascial  sheath  which  encloses  the  common  carotid  arteries, 
the  internal  jugular  vein  and  the  vagus  nerve,  as  they  lie  in 
the  angular  interval  between  the  sterno-mastoid  laterally,  the 
thyreoid  gland,  the  trachea,  oesophagus  medially,  and  the 
prevertebral  muscles  posteriorly.  The  ^rsf  or  superficial  layer, 
as  it  is  traced  posteriorly,  splits  to  enclose  the  sterno-mastoid 
muscle.  Beyond  the  sterno  -  mastoid  it  passes  posteriorly 
to  the  anterior  border  of  the  trapezius  muscle,  forming  the 
roof  of  the  posterior  triangle,  then  splits  again  to  enclose  the 
trapezius,  along  the  surfaces  of  which  it  is  prolonged  till  it 
blends  with  the  supraspinous  ligaments  and  the  ligamentum 


236 


HEAD  AND  NECK 


nuchse.  The  lamella  which  covers  the  deep  surface  of  the 
sterno-mastoid  is  blended  with  the  lateral  surface  of  the  carotid 
sheath.  The  pretracheal  layer,  which  has  been  dissected 
already  in  the  median  plane,  ensheaths  the  thyreoid  gland 
and  blends  postero-laterally  with  the  medial  surface  of  the 
carotid  sheath.  The  prevertebral  layer  covers  the  anterior 
surfaces  of  the  prevertebral  muscles  and,  passing  laterally, 
blends  with  the  posterior  aspect  of  the  carotid  sheath ;  then, 

turning  round  the  tips 
of  the  transverse  pro- 
cesses of  the  vertebrae, 
it  passes  posteriorly, 
covering  the  muscles 
which  form  the  floor  of 
the  posterior  triangle ; 
and  it  becomes  continu- 
ous with  the  sheaths  of 
the  deep  muscles  of  the 
posterior  part  of  the  neck. 
Laterally  and  pos- 
teriorly, the  superficial 
layer  of  the  deep  fascia 
passes  upwards  over  the 
sterno-mastoid  and  the 
trapezius  to  be  attached 
to  the  superior  nuchal 
lines  and  the  mastoid 
portions  of  the  temporal 
bones.  In  the  anterior 
cervical  region  it  is  attached  to  the  body  and  the  great  cornua 
of  the  hyoid  bone,  and  then,  as  it  is  prolonged  further  upwards, 
it  splits  anteriorly  to  enclose  the  submaxillary  gland,  and 
posteriorly  to  enclose  the  parotid.  It  has  been  noted  already 
that  the  lamella  which  passes  superficial  to  the  submaxillary 
gland  is  attached  to  the  lower  border  of  the  mandible,  and 
that  which  passes  deep  to  the  gland  is  connected  above  to 
the  mylo-hyoid  line  on  the  inner  surface  of  the  mandible.  The 
layer  which  passes  superficial  to  the  parotid  gains  attachment 
to  the  zygoma  and  is  prolonged  forwards  to  blend  with  the 
fascia  covering  the  masseter.  The  lamella  which  passes  deep 
to  the  parotid  covers  its  postero-medial  and  antero-medial 
surfaces ;   the  posterior  part  is  attached  above  to  the  lower 


First  layer  of  deep  fascia 
Pretracheal  layer 

Isthmus  of  thyreoid  gland 
Prevertebral  fascia 

First  layer    ffl 
Second  layer 
Pretracheal  layer 
Left  innominate  vein 


Mediastinal  tissue 


Fig.  95. — Diagram  of  deep  cervical  fascia 
in  sagittal  section. 


THE  ANTERIOR  PART  OF  THE  NECK      237 


First  layer  of  deep  fascia 

Thyreoid  gland 


Pretracheal  fascia 


Carotid 
sheath 


Prevertebral 
layer 


border  of  the  tympanic  plate  and  the  anterior  part  to  the 
posterior  border  of  the  petro-tympanic  fissure  (O.T.  Glaserian). 
It  also  gains  an  intermediate  attachment  to  the  styloid 
process  and  to  the  posterior  border  of  the  angle  of  the 
mandible.  This  particular  portion  is  relatively  thick ;  it  lies 
in  relation  with  the  lower  part  of  the  antero-medial  surface  of 
the  parotid  and  is  known  as  the  stylo-7na7idibular  ligament. 

When  the  superficial  layer  is  traced  downwards  it  is  found 
to  split,  between  the  cricoid  cartilage  and  the  sternum,  into  two 
lamellae.  The  more  superficial  of  the  two  lies  superficial  to 
the  sterno-mastoid  and  is  at- 
tached below  to  the  upper 
border  of  the  sternum  and  the 
upper  border  of  the  clavicle. 
In  the  anterior  region  the 
deeper  lamella  descends  upon 
the  anterior  surfaces  of  the 
infra-hyoid  muscles  and  is  at- 
tached below  to  the  posterior 
surface  of  the  manubrium ; 
laterally  it  passes  deep  to  the 
sterno  -  mastoid  and  is  fused 
with  the  lateral  border  of  the 
carotid  sheath.  In  the  posterior 
triangle  the  deeper  lamella 
ensheaths  the  posterior  belly 
of  the  omo-hyoid  and  binds  it 
down  to  the  posterior  border 
of  the  clavicle.  The  space 
between  the  two  lamellae  has 
been  called  the  supra-sternal 
space.  Its  boundaries  and  contents  have  been  fully  described 
already  (p.  224). 

The  upper  attachment  of  the  pretracheal  layer  is  to  the 
cricoid  cartilage  and  to  the  laminae  of  the  thyreoid  cartilage 
below  the  insertion  of  the  sterno-thyreoid  muscle.  At  its 
lower  end  it  blends  with  the  fibrous  pericardium  in  the 
middle  mediastinum. 

The  prevertebral  layer  can  be  followed  upwards  to  the 
base  of  the  skull,  where  it  is  attached,  in  the  anterior  cervical 
region,  to  the  posterior  and  medial  margins  of  the  jugular 
foramen  and  to  the  basilar  part  of  the  occipital  bone,  anterior 


IG.  96.  — Diagram  of  deep  cervical 
fascia  in  transverse  section  at  the 
level  of  the  thyreoid  gland. 


238 


HEAD  AND  NECK 


to  the  insertions  of  the  prevertebral  muscles  and  posterior  to 
the  superior  constrictor  of  the  pharynx.  Below,  it  blends 
with  the  fascia  on  the  anterior  aspect  of  the  vertebral  column 
in  the  posterior  mediastinal  region. 

The  Carotid  Sheath. — The  term  carotid  sheath  is  applied 
to  the  fascia  which  surrounds  and  embeds  the  carotid  arteries, 
the  internal  jugular  vein,  and  the  vagus  nerve.  Part  of  it  has 
been  removed  already,  and  the  dissector  will  have  noted  that 
it  is  in  no  sense  a  membrane,  but  merely  the  fibro-areolar 
tissue  which  fills  the  interval  between  the  transverse  processes 
of  the  vertebrae  posteriorly,  the  trachea,  larynx,  pharynx, 
oesophagus,  and  the  lateral  lobe  of  the  thyreoid  gland  medially, 
and  the  sterno-mastoid  laterally ;  that  it  is  continuous  with 
the  fascial  planes  in  its  immediate  neighbourhood,  and  that 

Fivst  layer  of  deep  fascia 


Infra-hyoid  muscl 


Scalene  muscle 


Omo-hyold 
Trapezius 


Sterno-mastoid 

Second  layer  of  deep  fascia 
Omo-hyoid 
Trapezius 


Fig.  97.  — Diagram  of  the  deep  cervical  fascia  in  a  transverse 
section  of  the  lower  part  of  the  neck. 

through  it  run  the  carotid  arteries,  the  internal  jugular  vein, 
and  the  vagus  nerve,  each  in  its  own  special  compartment. 

Dissection. — Remove  the  areolar  tissue  and  the  glands  v^^hich  lie  under 
cover  of  the  sterno-mastoid  ;  stitch  together  the  two  parts  of  the  divided 
anterior  belly  of  the  omo-hyoid  muscle  and  fix  the  muscle  to  the  common 
carotid  artery  and  the  internal  jugular  vein  with  one  or  two  stitches  ;  then 
proceed  to  display  the  structures  which  lie  under  cover  of  the  sterno-mastoid. 
A  glance  at  the  following  list  will  convince  the  dissector  that  they  are 
extremely  numerous. 


Structures  beneath  the  Sterno-Mastoid 

Muscles.- — The  upper  part  of  the  splenius  capitis ;  the 
upper  and  posterior  part  of  the  posterior  belly  of  the  digastric; 
the  origins  of  the  levator  scapulae,  the  scalenus  medius,  the 
longus  capitis  (O.T.  rectus  capitis  anticus  major),  the  rectus 
capitis  lateralis  and  the  scalenus  anterior  ;  the  intermediate 


THE  ANTERIOR  PART  OF  THE  NECK      239 

tendon  of  the  omo-hyoid,  and  the  lower  and  posterior  part  of 
the  sterno-hyoid  and  sterno-thyreoid. 

Arteries. — The  upper  part  of  the  common  carotid  (the 
lower  part  is  still  concealed  by  the  lower  parts  of  the  omo- 
hyoid and  the  lower  parts  of  the  sterno-hyoid  and  sterno- 
thyreoid  muscles);  the  transverse  scapular  and  its  sterno- 
mastoid  branch ;  the  transverse  cervical ;  the  sterno-mastoid 
branch  of  the  superior  thyreoid ;  the  occipital  and  its  sterno- 
mastoid  branches. 

Veins. — The  greater  part  of  the  internal  jugular  vein ;  a 
part  of  the  lower  transverse  portion  of  the  anterior  jugular 
vein  ;  and,  occasionally,  the  lower  end  of  the  external  jugular 
vein  when  that  vessel  dips  anteriorly  to  its  termination. 

Nerves. — The  cervical  plexus  and  its  branches,  including 
the  phrenic  nerve ;  part  of  the  accessory  nerve. 

If  the  lower  parts  of  the  divided  sterno-hyoid  and  sterno- 
thyreoid  muscles  are  displaced  downwards,  the  lower  part  of 
the  common  carotid  and  the  commencement  of  the  first  part  of 
the  subclavian  artery  will  be  exposed.  Crossing  the  front  of 
the  latter  are  the  lower  portion  of  the  cervical  part  of  the  vagus 
and  a  strand  of  sympathetic  fibres  called  the  ansa  subclavia  ; 
on  the  left  side,  the  subclavian  artery  and  the  ansa  are  con- 
cealed  by  the  commencement  of  the  innominate  vein.  At 
the  same  time  the  middle  thyreoid  vein  will  be  exposed, 
and  the  posterior  border  of  the  lateral  lobe  of  the  thyreoid 
gland  also. 

Dissection.— CowwwtncQ  by  cleaning  the  anterior  branches  of  the  cervical 
nerves  from  the  second  to  the  eighth,  as  they  emerge  between  the  muscles 
attached  to  the  tubercles  of  the  transverse  processes  of  the  cervical 
vertebrae.  The  first  nerve,  which  turns  downwards  anterior  to  the  trans- 
verse process  of  the  atlas,  will  be  exposed  later.  As  the  upper  nerves  are 
cleaned  the  dissectors  will  find  that  the  second  is  connected  to  the  third, 
and  the  third  to  the  fourth,  by  looped  strands,  convex  posteriorly,  which 
constitute  the  two  lower  loops  of  the  cervical  plexus.  The  second  nerve  is 
connected  with  the  first  also  by  a  loop,  convex  anteriorly,  which  passes 
upwards  anterior  to  the  transverse  process  of  the  atlas  and  posterior  to  the 
upper  part  of  the  internal  jugular  vein.  It  can  be  exposed  if  the  vein  is  pulled 
anteriorly  ;  and  the  dissector  must  at  the  same  time  secure  the  twigs  of 
connection  which  pass  from  the  medial  side  of  the  loop  to  the  hypoglossal 
nerve  and  to  the  superior  cervical  gangHon  of  the  sympathetic  trunk,  which 
lies  behind  the  upper  part  of  the  internal  carotid  artery. 

After  he  has  defined  the  loops  of  the  plexus  he  should  trace  the  remains 
of  the  small  occipital,  the  great  auricular,  the  transverse  cutaneous  nerve  of 
the  neck  and  the  supraclavicular  branches,  which  he  displayed  in  the 
posterior  triangle,  to  their  origins  from  the  roots  of  the  plexus.  The 
communicating  branches  which  pass  anteriorly  to  the  descendens  hypoglossi 
from  the  second,  and  sometimes  also  from  the  third  cervical  nerve,  must  be 


240 


HEAD  AND  NECK 


followed  ;  they  may  cross  either  superficial  or  deep  to  the  internal  jugular 
vein.  Then  the  phrenic  nerve,  which  springs  from  the  fourth  cervical 
nerve,  and  receives  additional  twigs  from  the  third  and  fifth  nerves,  must 
be  followed  downwards  and  anteriorly  till  it  disappears  under  cover  of  the 
lower  part  of  the  internal  jugular  vein.  It  lies  upon  the  surface  of  the 
scalenus  anterior  and  passes  deep  to  the  omo-hyoid  muscle  and  the  trans- 
verse cervical  and  transverse  scapular  arteries.  Running  parallel  with, 
and  anterior  to  it,  is  the  ascending  cervical  branch  of  the  inferior  thyreoid 
artery. 


Small  occipital  J  R 
Great  auricular 


Hypoglossal 


Nervus  cutaneus  colli 


Branch  to  levator 
scapulae 


Branch  to  levator 
scapulae 


Descending  trunk 


To  genio-hyoid 

Thyreo-hyoid  nerve 
Descendens  hypoglossi 


Ansa  hypoglossi 


Fig. 


Phrenic 


-Diagram  of  the  Cervical  Plexus  and  the  Ansa 
Hypoglossi. 


I,  II,  III,  IV. — Anterior  branches  of  the  upper  four  cervical  nerves. 


R.   Branches  to  recti  and  longus  capitis. 
S.M.  Branches  to  the  sterno-mastoid. 
C.C.  Rami  communicantes  cervicales. 


C.H.  Communicating    branch   to   hypo- 
glossal. 


This  diagram  shows  that  the  descendens  hypoglossi,  the  branch  to  the 
thyreo-hyoid,  and  in  all  probability  the  branches  to  the  genio-hyoid,  are 
composed  of  fibres  given  to  the  hypoglossal  by  the  communicating  twigs 
it  receives  from  the  first  cervical  nerve. 


Plexus  Cervicalis. — This  is  a  looped  plexus  formed  by 
the  first  four  cervical  nerves.  It  lies  in  the  upper  part  of 
the  side  of  the  neck  under  cover  of  the  sterno-mastoid.  The 
upper  loop  of  the  plexus,  which  connects  the  first  and  second 
nerves  together,  is  directed  forwards  and  lies  between  the 
internal  jugular  vein  anteriorly,  and  the  transverse  process  of 
the  atlas   posteriorly.     The  second  and  third  loops,  which 


THE  ANTERIOR  PART  OF  THE  NECK      241 

unite  the  second  and  third  and  the  third  and  fourth  nerves 
are  directed  posteriorly  ;  and  they  Ue  on  the  superficial  surface 
of  the  upper  part  of  the  scalenus  medius  muscle.  The  first 
loop  is  connected  with  the  upper  gangUon  of  the  sympathetic 
trunk  and  with  the  hypoglossal  nerve ;  and  the  roots  of  the 
second,  third  and  fourth  nerves  also  are  connected,  by  grey 
rami,  with  the  upper  cervical  sympathetic  ganglion. 

The  branches  of  the  plexus  are  divisible  into  two  main 
groups,  the  superficial  and  the  deep.  The  deep  branches  are 
separable  into  two  groups  :  the  anterior,  which  run  forwards 
and  the  posterior,  which  run  backwards ;  and  the  superficial 
branches  are  classified  as  ascending,  transverse  and  descending. 
The  anterior  group  of  deep  brafiches  includes  :  (i)  the  ramus 
communicans  cervicalis,  and  (2)  the  phrenic  nerve. 

The  posterior  group  of  deep  branches  is  formed  by  :  (i)  The 
communicating  branches  to  the  accessory  nerve.  (2)  Branches 
of  supply  to  id)  the  sterno-mastoid  from  the  second  nerve ; 
{b)  the  levator  scapulae  from  the  third  and  fourth ;  {c) 
the  trapezius  from  the  third  and  fourth  ;  id)  the  scalenus 
medius  from  the  second,  third,  and  fourth.  (3)  Less  im- 
portant muscular  branches  from  the  first  loop  to  {a) 
the  rectus  capitis  lateralis ;  (^)  the  rectus  capitis  anterior 
(O.T.  rectus  capitis  anticus  minor) ;  {c)  the  longus  capitis 
(O.T.  rectus  capitis  anticus  major),  (4)  Muscular  branches 
from  the  third  and  fourth  nerves  to  the  longus  colli. 

The  ascending  group  of  superficial  branches  is  formed  by  the 
small  occipital  and  great  auricular  nerves.  The  transverse 
branch  is  the  nervus  cutaneus  colli,  and  the  desce?iding 
branches  are  the  supraclavicular  nerves.  All  the  superficial 
nerves  have  already  been  traced  in  the  earlier  stages  of  the 
dissection  (pp.  145,  146),  but  the  phrenic  nerve  requires 
careful  consideration. 

Nervus  Phrenicus. — The  importance  of  the  phrenic  nerve 
depends  upon  the  fact  that  it  is  the  nerve  of  supply  to  the 
chief  muscle  of  respiration,  the  diaphragm.  The  majority  of 
its  fibres  spring  from  the  fourth  cervical  nerve,  but  it  receives 
twigs  from  the  third  and,  not  uncommonly,  from  the  fifth 
nerve  also.  It  descends  from  the  neck  through  the  superior 
and  posterior  mediastinal  regions  of  the  thorax,  and,  after 
piercing  the  diaphragm,  it  is  distributed  on  its  lower  surface. 
Only  the  cervical  portion  of  the  nerve  belongs  to  the  dis- 
sector of  the  neck  ;  the  remainder  is  displayed  by  the  dissector 

VOL.  II 16 


242  HEAD  AND  NECK 

of  the  thorax  (p.  341).  In  the  neck  the  nerve  runs  down- 
wards and  anteriorly,  on  the  superficial  surface  of  the  scalenus 
anterior,  which  forms  its  deep  relation.  In  this  part  of  its 
course  it  is  covered  by  skin,  superficial  fascia  and  platysma, 
deep  fascia  and  sterno-mastoid;  and,  deep  to  the  sterno-mastoid, 
it  is  overlapped  by  the  internal  jugular  vein,  and  it  is  crossed 
by  the  omo-hyoid,  the  anterior  jugular  vein,  and  the  transverse 
cervical  and  transverse  scapular  arteries  on  both  sides  ;  on  the 
left  side  by  the  thoracic  duct,  and  on  the  right  side  by  the 
right  lymph  duct.  At  the  root  of  the  neck  it  passes  from  the 
medial  border  of  the  anterior  scalene  to  the  anterior  surface 
of  the  first  part  of  the  subclavian  artery ;  and  it  is  covered 
anteriorly  by  the  clavicle  on  both  sides,  by  the  subclavian 
vein  on  the  right  side,  and  by  the  commencement  of  the  in- 
nominate vein  on  the  left  side,  and  it  crosses  either  anterior 
or  posterior  to  the  internal  mammary  artery.  It  gives  off  no 
branches  in  the  neck,  but  it  sometimes  receives  a  communica- 
tion from  the  nerve  to  the  subclavius. 

After  the  dissector  has  completed  the  examination  of  the  formation,  the 
relations,  and  the  branches  of  the  cervical  plexus,  he  should  replace  the 
divided  infra-hyoid  muscles  in  position  and  study  their  attachments  and 
relations. 

The  Infra-hyoid  Muscles  are  a  series  of  flat,  band-like 
muscles  which  lie  upon  the  trachea,  thyreoid  gland,  and 
larynx.  They  are  disposed  in  two  strata — viz.,  the  omo-hyoid 
and  the  sterno-hyoid  constituting  a  superficial  layer ;  and 
the  sterno-thyreoid  and  thyreo-hyoid  a  deep  layer. 

Musculus  Omohyoideus. — This  is  a  two-bellied  muscle.  The 
posterior  belly  springs  from  the  upper  border  of  the  scapula 
and  the  upper  transverse  scapular  Hgament.  It  crosses  the 
posterior  triangle  of  the  neck,  dividing  it  into  occipital 
and  subclavian  portions,  and  terminates  under  cover  of  the 
sterno-mastoid  muscle  in  an  intermediate  tendon ;  and  it  is 
superficial  to  the  phrenic  nerve  and  the  scalenus  anterior. 
The  tendon  is  held  in  position  by  a  strong  process  of  cervical 
fascia  which  is  firmly  attached  below  to  the  sternum  and  the 
first  costal  cartilage.  The  anterior  belly  emerges  from  under 
cover  of  the  anterior  border  of  the  sterno-mastoid,  and  takes 
an  almost  vertical  course  through  the  anterior  triangle.  It  is 
inserted  into  the  lower  border  of  the  body  of  the  hyoid  bone, 
at  the  lateral  side  of  the  sterno-hyoid.  In  the  anterior 
triangle   of   the    neck    it   forms   the    boundary   between    the 


THE  ANTERIOR  PART  OF  THE  NECK       243 

carotid  and  the  muscular  subdivisions,  and  it  lies  superficial 
to  the  internal  jugular  vein,  the  common  carotid  artery,  the 
descendens  hypoglossi,  the  superior  thyreoid  artery,  the  ex- 
ternal laryngeal  nerve,  the  attachments  of  the  sterno-thyreoid 
and    thyreo-hyoid    muscles    to    the    lamina    of   the   thyreoid 


Anterior  focial  vein 

Mylo-hyoid 

muscle 

Common  facial 

vein 

Lingual  vein 

Small  occipital  N.. 

Great  auricular  N.' 

Ner\  us 

cutaneus  colli' 

Internal  jugular\ein' 

Descending 

cervical  "' 

nerves 
Brachial 
plexus 
External- 
jugular  vein 
Descendens 
hypoglossi 
Anterior  ^ 
jugular  vein  ^ 

Inferior 
thjTeoid  veins^" 


Platj'sma 


External  maxillary 
artery 

Parotid  gland 
Submental  lymph 
gland 
Submaxillarj'  gland 

Sterno-mastoid  artery 
Ext.  carotid  artery 

Sup.  thyreoid  artery 
Common  carotid 

artery 
Lymph  gland 

Thyreo-glossal  duct 
Omo-hyoid 


Crico-thyreoid 
Sterno-hyoid 


Isthmus  of  thj-reoid 
gland 


Sterno-thyreoid 


Fig.  99. — Dissection  of  the  Front  of  the  Neck. 

has  been  removed. 


The  Ri^ht  Sterno-mastoid 


cartilage;  and  immediately  below  its  insertion  it  covers  part 
of  the  thyreo-hyoid  membrane.  Both  bellies  are  supplied  by 
branches  from  the  aiisa  hypoglossi. 

Musculus  Sternohyoideiis. — This  arises  from  the  posterior 
aspect  of  the  medial  end  of  the  clavicle,  the  posterior 
sterno-clavicular  ligament,  and  the  posterior  surface  of  the 
manubrium.      It  is  inserted  into  the  lower  border  of  the  body 

11—16  a 


244  HEAD   AND  NECK 

of  the  hyoid  bone,  between  the  median  plane  and  the  insertion 
of  the  omo-hyoid.  A  short  distance  above  the  sternum  an 
oblique  tendinous  intersection  frequently  divides  it  into  two 
portions.  The  lower  part  of  the  muscle  is  covered  by  the 
sterno-mastoid,  and  it  is  crossed  by  the  anterior  jugular  vein. 
Its  principal  deep  relations  are  the  lower  part  of  the  common 
carotid  artery  and  the  sterno-thyreoid  muscle,  which  separates 
it  from  the  lateral  lobe  of  the  thyreoid  gland.  It  is  supplied 
by  branches  from  the  ansa  hypoglossi. 

Musculus  Sternothyreoideus. — This  muscle  lies  under  cover 
of  the  preceding  and  is  both  broader  and  shorter.  It  springs 
from  the  posterior  aspect  of  the  manubrium  sterni  and  from 
the  cartilage  of  the  first  rib.  Diverging  slightly  from  its 
fellow  as  it  ascends,  it  is  inserted  into  the  obhque  line  on 
the  lateral  face  of  the  lamina  of  the  thyreoid  cartilage.  An 
incomplete  tendinous  intersection  may  sometimes  be  noticed 
interrupting  its  muscular  fibres.  The  nerve  supply  is  derived 
from  the  ansa  hypoglossi.  In  the  neck  it  is  covered  in  the 
greater  part  of  its  extent  by  the  sterno-hyoid  j  but  the  posterior 
part  of  its  insertion  is  covered  by  the  anterior  belly  of  the 
omo-hyoid  ;  and  the  lower  and  anterior  part  is  covered  by  skin 
and  fascia  only.  The  nerve  supply  is  derived  from  the  ansa 
hypoglossi, 

Musculus  Thyreohyoideus. — This  muscle  lies  on  the  same 
plane  as  the  sterno-thyreoid,  and  may  be  regarded  as  its 
upward  continuation.  It  takes  origin  from  the  oblique  line 
on  the  outer  surface  of  the  lamina  of  the  thyreoid  cartilage, 
and  is  inserted  into  the  lower  border  of  the  great  cornu  of 
the  hyoid  bone  under  cover  of  the  omo-hyoid  muscle.  It 
conceals  part  of  the  lamina  of  the  thyreoid  cartilage  and 
the  lateral  part  of  the  thyreo-hyoid  membrane,  and  the 
aperture  in  the  membrane  through  which  the  laryngeal  branch 
of  the  superior  thyreoid  artery  and  the  internal  laryngeal 
nerve  enter  the  pharynx.  It  is  supplied  by  a  twig  from  the 
hypoglossal  nerve. 

Dissection. — The  dissectors  of  the  head  and  neck  should  now  proceed  to 
study  the  relations  of  the  common  carotid  and  subclavian  arteries,  the 
cervical  part  of  the  thoracic  duct,  and  the  dome  of  the  pleura,  before  these 
are  disturbed  by  the  dissectors  of  the  thorax.  Whilst  this  is  being  done, 
the  omo-hyoid  must  be  retained  in  position,  but  the  upper  and  lower  portions 
of  the  other  infra-hyoid  muscles  may  be  turned  upwards  and  downwards 
respectively. 

Remove  the  remains  of  the  fascial  sheath  from  around  the  common 


THE  ANTERIOR   PART  OF  THE  NECK       245 

carotid  artery  and  the  adjacent  part  of  the  internal  jugular  vein.  Separate 
the  vein  from  the  artery  and  clean  the  portion  of  the  vagus  nerve  which 
lies  between  them  on  a  posterior  plane.  Note  that  on  the  right  side  the 
nerve  crosses  the  anterior  surface  of  the  subclavian  artery,  and  there  gives 
off  its  recurrent  branch  ;  and  that  on  the  left  side  it  lies  medial  to  the  sub- 
clavian artery  on  an  anterior  plane. 

After  the  lower  parts  of  the  vagi  have  been  cleaned,  look  for  the  terminal 
part  of  the  thoracic  duct  on  the  left  side  and  for  the  right  lymphatic  duct  on 
the  right  side.  In  seeking  for  the  thoracic  duct  puU'the  lower  end  of  the 
left  internal  jugular  vein  aside  and  displace  the  common  carotid  artery 
anteriorly  ;  then  look  for  the  duct  as  it  turns  laterally  from  the  border  of 
the  cepophagus  a  little  below  the  level  of  the  cricoid  cartilage  ;  trace  it 
posterior  to  the  internal  jugular  vein  to  its  termination  in  the  commence- 
ment of  the  innominate  vein.  On  the  right  side  look  for  the  right  lymphatic 
duct  entering  the  innominate  vein  in  the  angle  of  union  of  the  internal 
jugular  and  subclavian  veins.  Next  look  for  the  cervical  portion  of  the 
sympathetic  trunk,  which  descends  posterior  to  the  common  carotid.  Clean 
the  nerve  trunk  carefully  and  clean  also  the  inferior  thyreoid  arter}-,  which 
crosses  anterior  or  posterior  to  it,  at  the  level  of  the  cricoid  cartilage.  Dis- 
place the  common  carotid  laterally,  and  in  the  angle  between  the  borders 
of  the  trachea  and  the  oesophagus  find  the  recurrent  branch  of  the  vagus  ; 
trace  it  upwards  to  the  point  where  it  disappears  under  cover  of  the  lateral 
lobe  of  the  thyreoid  gland,  and  downwards  to  the  subclavian  artery. 

Arteria  Carotis  Communis. — The  common  carotid  arises 
differently  on  the  two  sides.  On  the  right  side  it  springs 
from  the  termination  of  the  innominate  artery,  behind  the 
sterno-clavicular  joint,  and  on  the  left  side  from  the  aortic 
arch  in  the  superior  mediastinum.  The  left  artery  ascends 
to  the  back  of  the  left  sterno-clavicular  articulation.  From 
the  sterno-clavicular  joint  each  common  carotid  artery  runs 
upwards,  posteriorly,  and  slightly  laterally  to  the  upper  border 
of  the  thyreoid  cartilage,  which  lies  opposite  the  disc 
between  the  third  and  fourth  cervical  vertebrae ;  and  there  it 
ends  by  dividing  into  its  two  terminal  branches — the  internal 
and  the  external  carotid  arteries. 

Superficial  Relations.  —  Above  the  level  of  the  anterior 
belly  of  the  omo-hyoid  the  common  carotid  artery  is  covered 
by  the  skin,  the  superficial  fascia  and  the  platysma,  the  deep 
fascia  and  the  anterior  margin  of  the  sterno-mastoid.  It  is 
crossed  immediately  above  the  omo-hyoid  by  the  sterno- 
mastoid  branch  of  the  superior  thyreoid  artery  and,  at  a  higher 
level,  by  the  superior  thyreoid  vein  ;  and  it  is  overlapped  by 
the  anterior  margin  of  the  internal  jugular  vein.  In  the 
lower  part  of  its  extent  it  Hes  more  deeply :  its  superficial 
relations  are  the  skin  and  superficial  fascia,  the  deep  fascia 
and  the  sterno-mastoid;  the  anterior  jugular  vein,  crossing 
transversely,  deep  to  the  sterno-mastoid  and  above  the  upper 


246 


HEAD  AND  NECK 


border  of  the  clavicle ;  the  omo-hyoid,  the  sterno-hyoid,  and 
the  sterno  -  thyreoid  muscles.  Deep  to  the  muscles,  the 
branches  of  the  ansa  hypoglossi  descend  in  front  of  its 
sheath ;  and  the  middle  thyreoid  vein  crosses  it  to  join  the 
internal  jugular  vein. 

Posterior  to  it  lie  the  transverse  processes  of  the  cervical 
vertebrae  and  the  origins  of  the  longus  colli,  longus  capitis 
(O.T.  rectus  capitis  anticus  major),  and  the  scalenus  anterior. 
The  inferior  thyreoid  artery  crosses  posterior  to  it  at  the  level 
of  the  cricoid  cartilage ;  and  the  vertebral  artery  lies  between 
it  and  the  transverse  process  of  the  seventh  cervical  vertebra. 
On  the  right  side,  the  recurrent  branch  of  the  vagus  crosses 


Thyreo-hyoid  membrane 
Phca  vocalis 
Processus  vocalis 
Arytaenoid  cartilage 

Platysma 
Posterior  wall 
of  pharynx 
Retropharyn 
geal  space  /^ 

Carotid  sheath 


Sterno-hyoid 

Thyreo  hyoid 

Th^Teoid  cartilage 
^^^^Lj^    Omo  hyoid 
;^^^>^     Recessus  piriformis 
Superior  thyreoid 
Descendens 
hypoglossi 
(^^  Common  carotid 
iternal  jugular 

Vagus 


Scalenus  anterior 

Longus  colli 


Vertebral  artery 


Sympathetic  trunk 


Fig.  100.  — Transverse  section  through  the  Neck  at  the  level  of  upper 
part  of  Thyreoid  Cartilage. 


posterior  to  it,  immediately  above  its  origin ;  and  on  the  left 
side  the  thoracic  duct  turns  laterally  behind  it,  between  it 
and  the  vertebral  artery. 

To  its  medial  side,  below,  lie  the  trachea  and  oesophagus, 
with  the  recurrent  nerve  in  the  angle  between  their  adjacent 
borders ;  and  to  the  medial  side  of  its  upper  part  are  the 
larynx  and  pharynx.  The  lateral  lobe  of  the  thyreoid  gland 
lies  either  medial  to  the  artery,  separating  it  from  the 
oesophagus,  pharynx,  trachea,  and  larynx,  or  it  forms  a  direct 
anterior  relation  (Figs.  97,  loi).  Between  its  upper  extremity 
and  the  inferior  constrictor  muscle  of  the  pharynx  lies  the 
carotid  body.  As  a  rule,  the  terminal  divisions  are  the  only 
branches  of  the  common  carotid,  but  occasionally  the 
superior  thyreoid  or  the  ascending  pharyngeal  artery  arises 


THE  ANTERIOR  PART  OF  THE  NECK      247 

from  it,  instead  of  from  the  external  carotid.  This  is  more 
especially  the  case  when  the  division  of  the  common  carotid 
takes  place  at  a  higher  level  than  usual. 

Carotid  Body. — This  is  a  little  oval,  reddish-brown  body,  placed  upon 
the  deep  aspect  of  the  common  carotid  artery  at  the  point  where  it 
bifurcates.  To  expose  it,  therefore,  the  vessel  must  be  twisted  round  in 
such  a  manner  that  its  posterior  surface  comes  to  look  forwards.  It  is 
closely  connected  with  the  sympathetic  filaments  which  twine  around  the 
carotid  vessels  ;  and  in  structure  it  is  similar  in  its  nature  to  the  minute 
coccygeal  body,  which  rests  upon  the  anterior  aspect  of  the  coccyx.  It  is 
included,  therefore,  in  the  group  of  ductless  glands.  Entering  it  are 
numerous  minute  arterial  twigs,  which  take  origin  from  the  termination  of 
the  common  carotid  and  the  commencement  of  the  external  carotid.  The 
function  of  this  remarkable  little  body  is  quite  unknown.  ]Most  likely  it 
is  a  vestioial  structure. 


Anterior  jugular  vein 
Superior  thjTeoid  arter\ 
Pharynx,        ^ 
Descenden-i 
hypoglo-5^  ' 
Common  carotid  v^     X 

Internal  jugulai  "^ -"V^fe^ 

Vagus 
Sympathetic 


Sterno-hyoid  Crico-thyreoid 

Superior  thyreoid  artery 
-Sterno-thyreoid 

)escendens  hj-poglossi 
/Omo-hj-oid 

'Common  carotid 
'Vagus 
'Internal  jugular 
.Sympathetic 
trunk 
'Cers'ical  nerves 


Longus  colli 


Retro-pharjmgeal  space      Vertebral  artery 


Fig.  10 1. — Transverse  section  through  the  Neck  at  the  level  of  the 
Cricoid  Cartilage, 


Arteria  Subclavia. — The  relations  of  the  third  part  of  the 
subclavian  artery  were  examined  during  the  dissection  of  the 
posterior  triangle  (p.  151).  Those  of  the  first  and  second  parts 
must  now  be  studied.  On  the  right  side  a  small  portion  of  the 
first  part  is  already  exposed  between  the  lower  ends  of  the 
internal  jugular  vein  and  the  common  carotid  artery ;  the 
remainder  can  be  seen  if  the  internal  jugular  vein  is  drawn 
aside.  On  the  left  side  the  first  part  of  the  artery  is  concealed 
by  the  commencement  of  the  innominate  vein,  which  must  be 
pushed  aside.  On  both  sides  the  second  part  of  the  artery 
Hes  posterior  to  the  scalenus  anterior,  which  must  be  left  in 
position. 

The  subclavian  artery  is  the  first  portion  of  the  great 
arterial  trunk  which  carries  blood  for  the  supply  of  the  upper 

11—16  b 


248 


HEAD  AND  NECK 


extremity.  It  arises  differently  on  the  two  sides  of  the  body. 
On  the  right  side  it  takes  origin  behind  the  sterno-clavicular 
articulation  from  the   bifurcation  of   the  innominate   artery. 


Sterno-thyreoid 

Sympathetic 

Inferior  constrictor 

Thyreoid  gland 

dragged  forwards 


.External 
caiotid  artery  _ 
Internal  jugular  vein 

Scalenus  medius 


Inferior  thyreoid 
artery 

Inferior  laryngeal 

nerve 

CEsophagus 

Common  carotid 
artery 

Internal  jugular  vein 


Inferior' thyreoid  vein 

Innominate  artery 


Brachial  nerves 

.Subclavian 
essels 


^^     'Transverse  scapular  and 
\         cervical  arteries 

Thoracic  duct 
\         Pleura 
Internal  mammary  artery  and  phrenic  nerve 

Left  innominate  vein 


Fig.  102. — Deep  Dissection  of  the  Root  of  the  Neck  on  the  Left  Side  to  show 
the  Dome  of  the  Pleura  and  the  relations  of  the  Terminal  Part  of  the 
Thoracic  Duct.  The  sterno -mastoid  and  the  depressors  of  the  hyoid  and 
larynx  have  been  removed. 

On  the  left  side  it  arises  from  the  aortic  arch  in  the  superior 
mediastinum.  In  both  cases  it  takes  an  arched  course 
laterally  across  the  root  of  the  neck,  posterior  to  the  scalenus 
anterior  and  on  the  anterior  surface  of  the  cervical  dome  of 


THE  ANTERIOR  PART  OF  THE  NECK       249 


pleura,   a   short  distance   below   its  summit.      At   the   outer 
border  of  the  first  rib  it  becomes  the  axillary  artery. 

For  descriptive  purposes  the  artery  is  divided  into  three 
parts.     The  first  part  extends  from  the  origin  of  the  vessel 


•illlli'i'-/.  Basilar  artery 

—  Vertebral  artery 

Vertebral  artery 


Vertebral  artery 
5th  cervical  vertebra 
Scalenus  anterior 
Transverse  cervical  artery- 
Inferior  thyreoid  artery 
Thyreo-cervical  trunk 

Transverse  scapular  art. 

Superior  inter- 
costal arter>' 
Right  common 
carotid" 


Deep  cervical  artery 


Inferior  thyreoid  artery 
-  Scalenus  anterior 
Transverse  cervical 
artery 

Costo-cervical  trunk 
Transverse 
'scapular  artery 
Superior  intercostal  art. 
.Subclavian  artery 
Left  subclavian 
artery 

Left  common 
carotid 

I  nternal 

mammary 

artery 


-Diagram  of  Subclavian  Arteries  and  their 
branches. 

to  the  medial  margin  of  the  scalenus  anterior;  the  secojid 
portion  lies  posterior  to  that  muscle;  and  the  third  part 
extends  from  the  lateral  border  of  the  scalenus  anterior  to 
the  outer  border  of  the  first  rib. 

First  Part. — Owing  to  the  difference  of  origin,  the  relations 
of  the  first  portion  of  the  subclavian  artery  are  not  the  same 


250  HEAD  AND  NECK 

on  the  two  sides  of  the  body.  The  first  part  of  the  right 
subclavian  extends  obliquely  upwards  and  laterally,  and  at  its 
termination  at  the  medial  margin  of  the  scalenus  anterior 
it  has  reached  a  point  above  the  level  of  the  clavicle.  It  is 
placed  very  deeply.  Anteriorly,  it  is  covered  by  the  skin, 
superficial  fascia,  platysma,  deep  fascia,  and  three  muscular 
strata — viz.,  the  clavicular  origin  of  the  sterno-mastoid,  the 
sterno-hyoid,  and  the  sterno-thyreoid.  Three  veins  and  some 
nerves  are  placed  anterior  to  it.  At  the  medial  margin  of 
the  scalenus  anterior  it  is  crossed  by  the  internal  jugular 
and  vertebral  veins,  whilst  the  anterior  jugular  vein,  as  it 
passes  laterally  under  cover  of  the  sterno-mastoid,  is  separated 
from  it  by  the  sterno-hyoid  and  sterno-thyreoid  muscles.  The 
nerves  which  cross  anterior  to  it  are  the  vagus,  a  loop  from 
the  sympathetic  (ansa  subclavia),  and  in  some  cases  cardiac 
branches  of  the  vagus  and  sympathetic  as  they  run  to  the 
thorax.  At  the  lower  margin  of  the  artery  the  vagus  nerve 
gives  off  its  recurrent  branch. 

The  cervical  dome  of  the  pleura  is  both  below  and  posterior 
to  the  artery,  and  the  recurrent  branch  of  the  vagus  nerve 
hooks  round  below  and  ascends  posterior  to  it.^ 

On  the  left  side,  the  first  part  of  the  subclavian  ascends 
almost  vertically  from  its  origin  from  the  aortic  arch,  and, 
reaching  the  root  of  the  neck,  it  curves  laterally  across  the 
dome  of  the  pleura  to  the  medial  margin  of  the  scalenus 
anterior.  The  relations  of  the  cervical  part  are  somewhat 
different  from  those  on  the  right  side.  The  same  fascial 
and  muscular  layers,  and  the  same  nerves  and  veins,  are 
anterior  to  it.  Owing  to  its  different  direction,  however,  the 
nerves  and  veins  are  placed  more  or  less  parallel  to  it.  Three 
additional  relations  are  established — viz.,  the  phrenic  nerve  and 
the  left  innominate  vein  lie  anterior  to  it ;  and  the  thoracic 
duct  first  passes  upwards  in  relation  to  its  medial  or  right 
side,  and  then  arches  over  it  to  reach  the  angle  of  junction 
between  the  subclavian  and  internal  jugular  veins. 

The  recurrent  nerve  on  the  left  side  hooks  round  the  arch 
of  the  aorta,  and  lies  to  the  medial  side  of  the  subclavian 
artery. 

Second  Part. — The  second  portion  of  the  subclavian  artery 

^  If  the  lung  has  been  removed  by  the  dissector  of  the  thorax  the  lower 
and  posterior  relations  should  be  verified  by  examination  from  the  thoracic 
side. 


THE  ANTERIOR  PART  OF  THE  NECK       251 

forms  the  highest  part  or  summit  of  the  arch,  and  rises  from 
half  an  inch  to  an  inch  above  the  level  of  the  clavicle. 

In  this  part  of  its  course  the  vessel  is  not  so  deeply 
placed.  Anteriorly  it  is  covered  by — (i)  skin;  (2)  superficial 
fascia  and  platysma ;  (3)  deep  fascia;  (4)  clavicular  head 
of  the  sterno-mastoid ;  (5)  scalenus  anterior.  The  phrenic 
nerve  on  the  right  side  is  also  an  anterior  relation,  but  it  is 
separated  from  the  artery  by  the  medial  margin  of  the 
scalenus  anterior.  Posteriorly  and  inferiorly^  the  vessel  is  in 
relation  with  the  pleura,  Sibson's  fascia  intervening.  The 
subclavian  vein  lies  at  a  lower  level  than  the  artery  and  on 
an  anterior  plane,  and  is  separated  from  it  by  the  scalenus 
anterior. 

The  third  part  of  the  subclavian  artery  is  described  on 
p.  151. 

Branches  of  tlie  Subclavian  Artery. — Four  branches 
spring  from  the  subclavian  trunk  (Fig.  103).  Three  take 
origin,  as  a  general  rule,  from  the  first  part  of  the  artery 
close  to  the  scalenus  anterior,  and  one  from  the  second  part. 
They  are — 

(I.   Vertebral, 
r  Inferior  thyreoid 
_c    ^  ^     _,       I  2.   Thyreo-cervical  \  Transverse  cervical 

first  tart.       \  ■'  t^  , 

\  It ransverse  scapular. 

I  3.   Internal  mammary. 
From  the      f  ^     ^  .     ^  ( Superior  intercostal. 

second paH.      ^Costo-cervical.  [Deep  cervical. 

In  a  great  number  of  cases  a  branch  of  considerable  size  will  be 
observed  springing  from  the  third  part  of  the  subclavian  artery.  This, 
in  all  probability,  is  the  descending  branch  of  the  transverse  cervical, 
arising  directly  from  the  subclavian.  It  is  so  common  an  occurrence  that 
the  dissector  must  always  be  prepared  to  meet  it. 

Arteria  Vertebralis. — This  is  the  first  branch  which  is 
given  off  by  the  subclavian.  It  springs  from  the  upper  and 
posterior  aspect  of  the  trunk  about  a  quarter  of  an  inch  from 
the  m.edial  margin  of  the  scalenus  anterior  on  the  right  side, 
and  from  the  point  where  the  vessel  reaches  the  root  of  the 
neck  on  the  left  side.  Only  a  small  portion  of  it  is  seen  in 
the  present  dissection.  It  proceeds  upwards  in  the  interval 
between  the  longus  colli  and  the  scalenus  anterior  muscles, 
posterior  to  the  common  carotid,  and  disappears  into  the 
foramen  transversarium  of  the  transverse  process  of  the  sixth 
cervical  vertebra.     It  is  placed  very  deeply,  and  is  covered 


252  HEAD  AND  NECK 

anteriorly  by  its  companion   vein    and  the  common  carotid 
artery.     Numerous  large  sympathetic  twigs  accompany  it. 

The  vertebral  artery  on  the  left  side  is  posterior  to  the 
internal  jugular  vein  and  the  common  carotid  artery,  and  it 
is  crossed  by  the  thoracic  duct. 

The  vertebral  vein  issues  from  the  aperture  in  the  transverse 
process  of  the  sixth  cervical  vertebra.  It  passes  downwards, 
antero-lateral  to  its  companion  artery,  and  posterior  to  the 
internal  jugular  vein,  to  open  into  the  posterior  aspect  of  the 
commencement  of  the  corresponding  innominate  vein.  Near 
its  termination  it  crosses  the  subclavian  artery.  It  receives 
the  deep  cervical  and  the  anterior  vertebral  veins. 

Truncus  Thyreocervicalis  (O.T.  Thyroid  Axis). — This  is 
a  short  wide  trunk,  which  arises  from  the  anterior  aspect 
of  the  subclavian  artery,  close  to  the  medial  margin  of  the 
scalenus  anterior,  and  under  cover  of  the  internal  jugular  vein. 
It  lies  between  the  phrenic  and  vagus  nerves,  and  almost 
immediately  breaks  up  into  its  three  terminal  branches — viz., 
the  inferior  thyreoid,  the  transverse  scapular,  and  the  transverse 
cervical. 

Arteria  Thyreoidea  Inferior. — This  vessel  takes  a  sinuous 
course  to  reach  the  thyreoid  gland.  At  first,  it  ascends  for 
a  short  distance  along  the  medial  border  of  the  scalenus 
anterior,  and  under  cover  of  the  internal  jugular  vein  j  then, 
at  the  level  of  the  cricoid  cartilage,  it  turns  suddenly  medial- 
wards  and  passes  posterior  to  the  sympathetic,  the  vagus,  and 
the  common  carotid  artery,  to  the  posterior  border  of  the 
thyreoid  gland,  where  it  gives  off  branches  to  the  larynx  and 
then  descends  along  the  posterior  border  of  the  gland,  dis- 
tributing branches  to  its  substance  and  to  the  trachea  and  the 
oesophagus. 

The  following  branches  will  be  noticed  arising  from  the 
inferior  thyreoid  artery  : — 


1.  Ascending  cervical. 

2.  Inferior  laryngeal. 

3.  Tracheal. 

4.  Pharyngeal. 


5.  QEsophageal. 

6.  Glandular. 

7.  Muscular. 


Arteria  Cervicalis  Ascendens. — This  small  but  constant  vessel 
runs  upwards  in  the  interval  between  the  scalenus  anterior 
and  longus  capitis,  and  gives  branches  to  the  muscles  in 
front  of  the  vertebral  column.  It  also  gives  o^ spinal  branches^ 
which  enter  the  vertebral  canal  upon  the  spinal  nerves,  and 


THE  ANTERIOR  PART  OF  THE  NECK      253 

anastomose  with  branches  from  the  vertebral  artery.  The 
ultimate  distribution  of  the  spinal  branches  has  been  noticed 
already  (p.  193). 

Arieria  Laryngea  Inferior. — This  small  vessel  accompanies 
the  inferior  laryngeal  nerve  to  the  larynx.  The  tracheal^  oisopha- 
geal,  and  pharyngeal  bra?ickes  supply  the  trachea,  the  gullet, 
and  the  pharynx.  They  are  of  small  size,  and  anastomose 
with  the  bronchial  and  oesophageal  branches  of  the  thoracic 
aorta.  The  gla?idular  branches  are  usually  two  in  number. 
One  ascends  upon  the  posterior  aspect  of  the  lateral  lobe  of 
the  thyreoid  gland,  whilst  the  other  is  given  to  its  base  or 
lower  end.  They  inosculate  with  the  corresponding  vessels 
of  the  opposite  side,  and  also  with  the  branches  of  the 
superior  thyreoid  artery.  The  muscular  branches  are  a  series 
of  irregular  twigs  given  to  the  various  muscles  in  the 
neighbourhood. 

Vena  Thyreoidea  Inferior. — The  inferior  thyreoid  vein  does 
not  run  in  company  with  the  artery  of  the  same  name.  It  is  a 
comparatively  large  vessel  which  comes  from  the  lateral  lobe 
and  the  isthmus  of  the  thyreoid  gland,  and  descends  upon 
the  trachea  under  cover  of  the  sterno-thyreoid  muscle.  The 
veins  of  both  sides  enter  the  thorax,  and  frequently  unite  to 
form  a  short  common  stem,  which  opens  into  the  left  in- 
nominate trunk.  In  other  cases,  however,  the  right  vein 
will  be  observed  to  open  separately  into  the  angle  of  union 
between  the  two  innominate  veins.  Both  veins,  as  they 
proceed  dow^nwards,  receive  tributaries  from  the  larynx, 
trachea  and  oesophagus. 

The  afiterior  vertebral  vein  accompanies  the  ascending 
cervical  artery,  and  opens  into  the  vertebral  vein  as  it  issues 
from  the  foramen  transversarium  of  the  sixth  cervical  vertebra. 

The  Transverse  Scapular  and  Transverse  Cervical  Arteries. 
— Both  of  these  arteries  have  already  been  examined  in  the 
greater  part  of  their  courses  (p.  147).  After  taking  origin 
from  the  thyreo-cervical  trunk,  they  both  pass  laterally  across 
the  scalenus  anterior  muscle  and  the  phrenic  nerve  under 
cover  of  the  clavicular  head  of  the  sterno-mastoid.  The 
transverse  scapular  crosses  the  anterior  scalene  muscle  close 
to  its  insertion,  immediately  above  the  subclavian  vein ;  the 
transverse  cervical  is  placed  at  a  slightly  higher  level. 

The  transverse  scapular  and  transverse  cervical  veins  have 
already  been  seen  joining  the  external  jugular  vein. 


254  HEAD  AND  NECK 

Arteria  Mammaria  Interna. — The  internal  mammary  artery 
springs  from  the  lower  and  anterior  aspect  of  the  subclavian, 
directly  below  the  thyreo-cervical  trunk.  It  passes  downwards 
upon  the  anterior  surface  of  the  pleura,  posterior  to  the  medial 
end  of  the  clavicle  and  the  medial  end  of  the  subclavian  vein, 
to  reach  the  thorax.  As  it  lies  posterior  to  the  subclavian 
vein  the  phrenic  nerve  passes  from  the  lateral  to  the  medial 
side,  either  anterior  or  posterior  to  it.  In  the  neck  the  in- 
ternal mammary  artery  is  not  accompanied  by  a  vein. 

Truncus  Costocervicalis. — This  branch  takes  origin  from 
the  posterior  aspect  of  the  second  portion  of  the  subclavian 
artery,  close  to  the  medial  border  of  the  scalenus  anterior. 
On  the  left  side,  however,  it  proceeds,  as  a  rule,  from  the 
first  part  of  the  parent  trunk.  To  bring  it  into  view  the 
subclavian  artery  must  be  dislodged  from  its  position.  It 
is  a  short  trunk  which  passes  upwards  and  posteriorly  over 
the  apex  of  the  pleura  to  the  neck  of  the  first  rib,  where  it 
divides  into  the  deep  cervical  artery  and  the  superior  intercostal 
artery. 

If  the  lung  is  removed  from  the  thorax  the  dissector 
should  take  the  opportunity  of  examining  this  artery  from  the 
thoracic  aspect. 

Arteria  Cervicalis  Profunda. — This  branch  passes  dorsally 
and  disappears  from  view  between  the  transverse  process  of 
the  seventh  cervical  vertebra  and  the  neck  of  the  first  rib. 
It  has  been  already  noticed  in  the  dissection  of  the  back 
of  the  neck  (p.  173). 

The  deep  cervical  vein  is  a  large  vessel.  It  joins  the 
vertebral  vein. 

Arteria  Intercostalis  Suprema. — The  superior  intercostal 
artery  turns  downwards  anterior  to  the  neck  of  the  first  rib, 
between  the  first  thoracic  nerve  and  the  first  thoracic  ganglion 
of  the  sympathetic.  It  gives  a  posterior  intercostal  branch  to 
the  first  space  and  ends  as  the  posterior  intercostal  artery  of 
the  second  space  (Fig.  5). 

Vena  Subclavia. — The  subclavian  vein  is  the  continuation 
of  the  axillary  vein  into  the  root  of  the  neck.  It  begins 
at  the  outer  border  of  the  first  rib,  and  arches  medially 
on  the  anterior  surface  of  the  lower  end  of  the  scalenus 
anterior.  At  the  medial  margin  of  this  muscle,  and  posterior 
to  the  sternal  end  of  the  clavicle,  it  joins  with  the  internal 
jugular  to   form    the  innominate   vein.     In   connection  with 


THE  ANTERIOR  PART  OF  THE  NECK      255 

the  subclavian  vein  note:  (i)  that  the  arch  which  it  forms 
is  not  so  pronounced  as  the  arch  of  the  corresponding 
artery;  (2)  that  throughout  its  whole  course  it  lies  at  a 
lower  level,  and  upon  a  plane  anterior  to  the  artery ;  and 
(3)  that  it  is  separated  from  the  artery  by  the  scalenus 
anterior  and  the  phrenic  nerve.  In  the  whole  of  its  course 
the  vein  lies  posterior  to  the  clavicle. 

The  sheath  of  the  subclavian  vein  is  attached  to  the  posterior  surface  of 
the  costo-coracoid  membrane.  This  is  a  relation  of  some  practical  import- 
ance ;  for,  on  account  of  it,  a  forward  movement  of  the  clavicle  drags  upon 
the  vein,  and  in  cases  where  the  vessel  is  wounded  there  is  always  a  danger 
of  air  being  sucked  into  the  vein  by  such  a  movement. 

The  tributary  of  the  subclavian  vein  is  the  external  jugular 
vein,  which  joins  it  at  the  lateral  margin  of  the  scalenus 
anterior. 

Ductus  Thoracicus  et  Ductus  Lymphaticus  Dexter. — The 
thoracic  duct  is  the  vessel  by  means  of  which  the  chyle  and 
the  lymph,  derived  from  by  far  the  greater  part  of  the  body, 
are  poured  into  the  venous  system  on  the  left  side  (p.  106). 
Its  terminal  or  cervical  portion  is  displayed  in  the  dissection  of 
the  neck.  It  is  a  small,  thin-walled  vessel,  frequently  mistaken 
for  a  vein,  which  enters  the  root  of  the  neck  at  the  left 
margin  of  the  oesophagus.  It  is  there  that  it  should  be 
sought.  At  the  level  of  the  seventh  cervical  vertebra  it 
arches  laterally  and  anteriorly,  and  then  downwards,  above 
the  apex  of  the  pleura,  and  it  enters  the  innominate  vein  in  the 
angle  of  the  union  of  the  internal  jugular  vein  with  the 
subclavian.  As  the  thoracic  duct  courses  laterally  it  lies  at 
a  higher  level  than  the  subclavian  artery,  and  passes  posterior  to 
the  common  carotid  artery,  the  vagus  nerve  and  the  internal 
jugular  vein,  and  anterior  to  the  vertebral  artery  and  vein 
and  the  thyreo-cervical  artery  or  its  inferior  thyreoid  branch  ; 
and  as  it  runs  downwards  to  its  termination  it  is  separated 
from  the  scalenus  anterior  by  the  transverse  cervical  and 
transverse  scapular  arteries  and  the  phrenic  nerve.  Further, 
as  it  approaches  the  point  at  which  it  ends,  it  crosses  the 
first  part  of  the  subclavian  artery. 

A  valve  composed  of  two  segments  guards  its  entrance 
into  the  innominate  vein. 

Ductus  Lymphaticiis  Dexter. — The  right  lymph  duct  is 
the  corresponding  vessel  on  the  right  side,  but  it  is  a  com- 
paratively insignificant  channel  which  conveys  lymph  from  a 


256 


HEAD  AND  NECK 


much  more  restricted  area.  It  commences  in  the  posterior 
mediastinum,  where  it  not  uncommonly  communicates  with 
the  thoracic  duct ;  and  it  ascends  to  the  root  of  the  neck  on 


Clavicular  head  of 
sterno-mastoid 


Sterno-thyreoid 


Thyreoid  gland 
Phrenic  nerve 

Vagus 

Sternal  head  of, 
sterno-mastoid  ^~*7^, 

Sterno-hyoid 


Anterior  jugular  vein 
Clavicular  facet  on  sternum 

Left  common  carotid 

Left  innominate  vein 


External  jugular  vein 

Platysma  reflected  vi'Ith  skin 
Nervus  cutaneus  colli 

Internal  jugular  vein 


\  Supra-clavicular 
rl  nerves 


Omo-hyoid 

I  Transverse  cervical 
vein 

Brachial  plexus 

Scalenus  anterior 
Trans,  cervical  artery 
Trans,  scapular  artery 
External  jugular  vein 
.  Subclavius 
Cephalic  vein 
Axillary  vein 


First  rib 
Dome  of  left  pleura 
Thoracic  duct 
Internal  mammary  artery 
Phrenic  nerve 


Fig.  104. — Deep  Dissection  of  the  Root  of  the  Neck  on  the  Left  Side  to  show 
the  Dome  of  the  Pleura  and  the  relations  of  the  Terminal  Part  of  the 
Thoracic  Duct.  The  sterno-mastoid  and  the  depressors  of  the  hyoid  and 
larynx  have  been  removed. 

the  right  side,  where  it  terminates  in  the  commencement  of 
the  innominate  vein  by  opening  into  it  in  the  angle  of  union 
of  the  subclavian  and  internal  jugular  veins.  As  in  the  case  of 
the  thoracic  duct,  its  orifice  is  guarded  by  a  double  valve. 
Lymph  passes  to  it  from  the  intercostal  glands  which  lie  in 


THE  ANTERIOR  PART  OF  THE  NECK      257 

the  upper  interspaces  of  the  right  side,  and  from  the  thoracic 
visceral  glands  of  the  right  side.  About  half  an  inch  from 
its  termination  it  is  sometimes  joined  by  the  right  subclavian 
and  jugular  lymph  trunks,  which  convey  lymph  from  the 
right  upper  extremity  and  the  right  side  of  the  head  and 
neck,  respectively.  Under  these  circumstances  it  constitutes 
the  main  lymph  drain  for  the  following  districts:  (i)  right 
upper  limb;  (2)  right  side  of  the  head  and  neck;  (3)  upper 
part  of  right  thoracic  wall;  (4)  right  side  of  diaphragm 
and  upper  surface  of  liver;  (5)  thoracic  viscera  on  right 
side  of  median  plane,  viz.  right  side  of  heart  and  peri- 
cardium and  the  right  lung  and  pleura.  But  not  uncommonly 
the  right  jugular  and  subclavian  lymph  trunks  open 
separately  into  the  internal  jugular,  the  subclavian,  or  the 
innominate  vein. 

Cervical  Pleura. — The  pleural  sac  of  each  side,  with  the 
apex  of  the  corresponding  lung,  projects  upwards  into  the 
root  of  the  neck,  and  the  dissector  should  now  examine  the 
height  to  which  it  rises,  and  the  connections  which  it  estab- 
lishes (see  Figs,  i  and  5).  Its  height  with  reference  to  the 
first  pair  of  costal  arches  varies  in  different  subjects.  In 
some  cases  it  extends  upwards  for  two  inches  above  the 
sternal  end  of  the  first  rib ;  in  others  for  not  more  than  one 
inch.  These  differences  depend  on  the  degree  of  obliquity 
of  the  thoracic  inlet.  Posteriorly,  in  the  majority  of  cases, 
the  apex  of  the  pleura  corresponds  in  level  with  the  neck 
of  the  first  rib.  It  forms  a  dome-like  roof  for  each  side  of 
the  thoracic  cavity,  and  is  strengthened  by  a  fascial  expansion 
(frequently  termed  Sib  son' s  fascia),  which  covers  it  completely, 
and  is  attached  on  the  one  hand  to  the  transverse  process 
of  the  seventh  cervical  vertebra  and  on  the  other  to  the  inner 
margin  of  the  first  rib. 

Note  that  it  is  in  relation  with:  (i)  the  scalenus  anterior; 
(2)  the  scalenus  medius ;  (3)  the  subclavian  artery;  (4)  the 
vertebral  artery;  (5)  the  costo-cervical  trunk;  (6)  the  superior 
intercostal  artery;  (7)  the  internal  mammary  artery;  (8)  the 
innominate  vein;  (9)  the  vertebral  vein;  (10)  the  subclavian 
vein;  (i i)  the  vagus  nerve  ;  (12)  the  phrenic  nerve;  (13)  the 
recurrent  nerve  on  the  right  side;  (14)  the  first  thoracic 
nerve;  (15)  the  first  thoracic  ganglion  of  the  sympathetic; 
(16)  the  ansa  subclavia  (Vieusenii). 

The  scalenus  anterior  covers  the  antero-lateral  part  of  the 

VOL.  II — 17 


258 


HEAD  AND  NECK 


dome,  separating  it  from  the  subclavian  vein,  which  ends  at 
the  medial  border  of  the  muscle.  Immediately  above  the 
vein  the  subclavian  artery  crosses  the  dome  below  its  apex. 
The  internal  mammary  artery  descends  from  the  subclavian, 
passes  posterior  to  the  subclavian  vein,  and  is  crossed,  as  it 
lies  behind  the  vein,  by  the  phrenic  nerve,  which  passes  in 
some  cases  anterior  to,  and  in  others  posterior  to  the  artery. 


Parotid  duct 


Accessory  parotid  gland 

Internal  pterygoid 


Lingual  nerve 
Mandible 


Mylo-hyoid 
Surface  of  submaxil- 
lary gland  covered 
by  mandible 
Surface  covered  by 
integument  and  fasciae 


Mandible 

Submaxillary  duct' 
Mucous  membrane 
Sublingual  gland 

Tongue' 

Mylo-hyoid'       /        _ 
Anterior  belly  of  digastric 

Fig.  105. — Dissection  of  the  Parotid,  Submaxillary,  and  Sublingual  Glands. 

The  costo-cervical  artery  ascends  from  the  subclavian  and 
crosses  the  apex  of  the  dome ;  its  superior  intercostal  branch 
descends,  posterior  to  the  apex,  between  the  first  intercostal 
nerve  on  the  lateral  side,  and  the  first  thoracic  sympathetic 
ganglion  on  the  medial  side.  The  vagus  nerve  descends 
anterior  to  the  medial  part  of  the  subclavian  artery,  and,  on 
the  right  side,  its  recurrent  branch  turns  round  the  lower 
border  of  the  artery;  the  ansa  subclavia  lies  to  the  lateral 
side  of  the  recurrent  nerve. 


PAROTID  GLAND 


259 


It  is  not  possible  to  examine  the  relations  of  either  the  whole  of  the 
internal  jugular  vein  or  the  external  carotid  artery,  or  the  whole  of  the 
cervical  portion  of  the  internal  carotid,  until  the  parotid  gland  has  been 
removed,  the  infratemporal  and  submaxillary  regions  have  been  dissected, 
and  the  posterior  belly  of  the  digastric  and  the  styloid  process  have  been 
detached  and  displaced  anteriorly.  It  is  important,  however,  that  the 
internal  jugular  vein  should  be  retained  in  position  whilst  these  parts  of 
the  dissection  are  being  proceeded  with;  the  dissector  should  therefore 
stitch  the  subclavian  vein  to  the  anterior  surface  of  the  scalenus  anterior, 
and  the  lower  part  of  the  internal  jugular  vein  to  the  first  part  of  the  sub- 
clavian artery,  before  proceeding  to  the  study  and  removal  of  the  parotid 
gland. 


r.  Posterior  facial  vein 

2.  Sterno-mastoid 

3.  Digastric 

4.  Accessory  nerve 

5.  Internal  jugular 

6.  Stylo-hyoid 

7.  Glossopharyngeal 

ner\e 


4567 


Quadratus  labii  superioris 

Maxillary  sinus 
Zygomaticus 

Buccinator  muscle 

Temporal  muscle 

Tonsil 

Inferior  alveolar  vessels 
and  nerve 

Pharynx 

S  tyl  o-pharyngeus 
Stylo-glossus 
Internal  carotid 
Sympathetic 
Vagus  and  Hypoglossal 


Fig.  106. — Transverse  section  through  the  Head  at  the  level  of  the  Hard 
Palate.      It  shows  the  relations  of  the  parotid  gland,  etc. 

Glandula  Parotis. — The  parotid  gland  is  wedged  into  a 
more  or  less  triangular  interval,  the  parotid  space,  which  is 
bounded  anteriorly  by  the  posterior  borders  of  the  masseter, 
the  ramus  of  the  mandible,  and  the  internal  pterygoid,  and 
postero-medially  by  the  anterior  border  of  the  sterno-mastoid, 
the  mastoid  process,  the  posterior  belly  of  the  digastric,  the 
styloid  process,  and  the  stylo-hyoid  muscle.  The  space 
extends  upwards  to  the  external  acustic  meatus,  and  it  is 
prolonged  downwards  into  the  carotid  triangle,  into  which 
II — 17  a 


26o 


HEAD  AND  NECK 


the  lower  extremity  of  the  gland  descends  for  a  short 
distance  beyond  the  angle  of  the  mandible.  The  gland, 
however,  is  more  extensive  than  the  space  and  passes  for  a 
varying  distance  forwards  beyond  its  anterior  border  over  the 
superficial  surface  of  the  masseter. 

In  accordance  with  the  position  which  it  occupies  the 
gland  may  be  described  as  possessing  three  surfaces,  two 
extremities,  and  four  borders.  The  surfaces  are  superficial 
or  lateral,  postero-medial,  and  antero-medial;  the  extremities, 
upper  and  lower ;  the  borders,  anterior,  posterior,  medial,  and 


Anterior  border  of  upper  extremity 


Posterior  border 
of  upper  end 


Surface  in  contact  with  external  meatus 
Anterior  border 


Duct  of  parotid 
_, Superficial  surface 


External  jugular  vein 

Posterior  border 

Fig.   107.  —  Parotid  Gland,  lateral  view. 

superior.  The  medial  border  separates  the  antero-medial 
from  the  postero-medial  surface.  The  anterior  and  posterior 
borders  separate  the  lateral  surface  from  the  antero-medial 
and  postero-medial  surfaces,  respectively.  The  upper  border 
intervenes  between  the  upper  surface  and  the  other  three 
surfaces. 

The  superficial  surface  is  triangular  in  outline  (Fig.  105).  It 
is  covered  by  skin,  superficial  fascia,  platysma  and  risorius,  and 
deep  fascia.  Embedded  in  it  are  a  few  superficial  parotid 
lymph  glands,  which  receive  lymph  from  the  anterior  part  of 
the  scalp,  the  face  above  the  level  of  the  mouth,  and  from 
the  lateral  surface  of  the  auricle.  Posteriorly,  it  is  in 
relation  with  the  mastoid  process  and  the  anterior  border  of 


PAROTID  GLAND  261 

the  sterno-mastoid  muscle.  Above,  it  touches  the  posterior 
part  of  the  lower  border  of  the  zygoma  and  the  lower  surface 
of  the  external  meatus. 

From  beneath  the  part  in  contact  with  the  zygoma  emerge 
the  auriculo-temporal  nerve,  the  temporal  branches  of  the 
facial  nerve,  and  the  superficial  temporal  artery,  on  their  way  to 
the  scalp  ;  and  the  posterior  facial  vein  disappears  under  cover 
of  it.  Its  lower  extremity,  which  is  wedged  between  the  angle 
of  the  mandible  and  the  anterior  border  of  the  sterno-mastoid, 
is  usually  in  contact  with  one  of  the  upper  deep  cervical 
glands,  whilst  the  posterior  facial  vein,  the  commencement  of 
the  external  jugular  vein,  and  the  cervical  branch  of  the  facial 
nerve  emerge  from  it ;  the  former  passing  downwards  and 
posteriorly,  and  the  two  latter  downwards  and  anteriorly. 

From  beneath  the  anterior  border,  which  rests  upon  the 
masseter,  the  duct  of  the  gland  (Stensen's),  the  transverse 
facial  artery,  and  the  zygomatic,  buccal,  and  mandibular 
branches  of  the  facial  nerve  pass  forwards  ;  and  the  transverse 
facial  vein  disappears  under  cover  of  it. 

The  duct  of  the  parotid  gland  (Stensen's),  after  appearing 
from  under  cover  of  the  anterior  border  of  the  gland,  runs 
anteriorly  across  the  masseter,  at  the  level  of  a  line  drawn 
from  the  lobule  of  the  auricle  to  a  point  situated  midway 
between  the  red  margin  of  the  upper  lip  and  the  ala  of 
the  nose.  At  the  anterior  border  of  the  masseter  it  turns 
inwards,  at  right  angles  to  its  former  course,  and  after  piercing 
the  sucking  pad  of  fat,  the  buccinator  fascia,  the  buccinator 
muscle  and  the  mucous  membrane  of  the  vestibule  of  the 
mouth,  it  opens  into  the  vestibule,  on  the  apex  of  a  papilla, 
opposite  the  second  molar  tooth  of  the  maxilla. 

Immediately  anterior  to  the  anterior  border  of  the  gland, 
below  the  zygoma  and  above  the  duct,  lies  a  small  separated 
portion  of  the  gland  substance  called  the  accessory  parotid ;  its 
duct  opens  into  the  main  duct. 

Dissection. — The  gland  must  be  removed  piecemeal  as  the  structures 
which  pass  through  it  are  dissected  out.  The  facial  nerve  and  its  branches 
are  the  most  superficial  structures  in  the  substance  of  the  parotid  ;  therefore 
they  must  be  dissected  first.  Trace  the  terminal  branches  posteriorly  into 
the  gland  until  they  join  the  main  divisions,  which  are  the  zipper  ox  temporo- 
facial  and  the  lower  or  ce>-vico-facial.  The  temporal  and  zygomatic  branches 
spring  from  the  temporo-facial  division,  the  buccal,  mandibular,  and  cervical 
from  the  cervico -facial  division.  Follow  the  divisions  posteriorly  across 
the  posterior  facial  vein  to  their  union  with  the  trunk  of  the  nerve,  which 
pierces  the  postero-medial  surface  of  the  gland  ;  then  trace  the  trunk  across 
11—17  h 


262  HEAD  AND  NECK 

the  root  of  the  styloid  process  to  the  stylo-mastoid  foramen  and  secure  the 
branch  which  springs  from  it  to  supply  the  posterior  belly  of  the  digastric 
and  the  stylo-hyoid  muscles,  and  the  posterior  auricular  branch.  As  the  trunk 
of  the  nerve  is  being  cleaned  the  posterior  auricular  branch  of  the  external 
carotid  artery  will  probably  be  exposed,  passing  upwards  and  posteriorly 
along  the  upper  border  of  the  posterior  belly  of  the  digastric  to  the  back  of 
the  external  meatus,  and  crossing  either  superficial  or  deep  to  the  nerve. 
Next,  remove  the  deeper  parts  of  the  gland  and  expose  Ae  posterior  facial 
vein,  descending  towards  the  angle  of  the  mandible.  It  receives  the  trans- 
verse facial  and  the  internal  maxillary  veins,  and  it  gives  off  the  commence- 
ment of  the  external  jugular  vein  ;  and  then  it  passes  out  of  the  lower  end  of 
the  gland  and  unites  with  the  anterior  facial  vein  to  form  the  common  facial 
vein.  Deep  to  the  veins  will  be  found  the  upper  end  of  the  external 
carotid  artery  dividing  into  its  superficial  temporal  and  internal  maxillary 
branches  ;  and  the  transverse  facial  and  middle  temporal  offsets  of  the 
superficial  temporal  will  also  be  displayed. 

When  the  remains  of  the  deeper  part  of  the  gland  have  been  removed, 
the  styloid  process  with  the  origin  of  the  stylo-hyoid  muscle,  and  the 
posterior  belly  of  the  digastric  will  be  exposed  ;  and  the  internal  jugular  vein 
and  the  internal  and  external  carotid  arteries  will  be  seen  disappearing 
under  cover  of  the  digastric.  If  the  occipital  artery  lies  at  its  lower  level, 
it  also  will  be  noted  as  it  runs  upwards  and  posteriorly,  along  the  lower 
border  of  the  digastric,  crossing  superficial  to  the  two  large  vessels,  and 
to  the  accessory  nerve,  \yhich  emerges  from  under  cover  of  the  digastric  and 
passes  downwards  and  posteriorly  across  the  internal  jugular  vein. 

The  dissector  should  now  obtain  a  gland  which  has  been 
removed  uninjured  from  the  parotid  space,  or  a  cast  of  a 
gland,  and  proceed  to  study  the  relations  of  the  upper  end 
and  the  postero-medial  and  antero-medial  surfaces. 

The  upper  extremity  presents  a  deep  concavity  which  is 
usually  separable  into  a  larger  lateral  part  which  lies  in 
contact  with  the  cartilaginous  part  of  the  external  meatus, 
^nd  a  smaller  medial  part  which  touches  the  bony  wall  of  the 
meatus  (Fig.  109).  The  anterior  boundary  of  the  upper 
end  forms  a  sharp  ridge,  which  lies  in  the  narrow  interval 
between  the  capsule  of  the  temporo-mandibular  articulation 
and  the  front  of  the  external  meatus. 

Th-Q  postero-7?tedial  surface  is  marked  by  a  series  of  depres- 
sions which  correspond  with  the  structures  in  the  postero- 
medial boundary  of  the  parotid  space.  Above  is  a  shallow 
depression  corresponding  with  the  anterior  border  of  the 
mastoid  process,  and  below  the  latter  a  groove  caused  by  the 
anterior  border  of  the  sterno-mastoid.  More  medially  is  a 
shallow  depression  due  to  the  posterior  belly  of  the  digastric 
and  the  stylo-hyoid,  and,  still  more  medially  and  at  a  higher 
level,  a  sulcus  which  corresponds  with  the  position  of  the 
styloid  process.  Below  the  level  of  the  digastric  groove  the 
postero-medial  surface  covers  portions  of  the  internal  jugular 


PAROTID  GLAND 


263 


vein  and  the  internal  and  external  carotid  arteries.  The 
commencement  of  the  external  jugular  vein,  the  posterior 
facial  vein,  and  the  cervical  brancJi  of  the  facial  nerve  emerge 
from  this  part  of  the  surface.  Immediately  above  the  digastric 
groove,  close  to  the  medial  border,  the  external  carotid  enters 
the  gland ;  and  directly  lateral  to  the  upper  end  of  the  groove 
for  the  styloid  process  the  facial  nerve  passes  into  the  gland 
substance.  The  dissector  should  note  that  the  postero-medial 
surface  of  the  gland  is  separated  from  the  upper  parts  of  the 
internal  jugular  vein  and  the  internal  carotid  artery,  and  from 

Anterior  border  of  upper  extremity' 
Area  for  cartilage  of  external  meatus 

Area  for  bone  of  external  meatus  v^_^^: 
Postero-medial  border  of  upper  end 
Mastoid  area. 

Styloid  area * 

Facial  nerve--— — vf 

■      ■  1/   ' 

Posterior  auricular  arterj  -^^ 

Ridge  between  digastric 
and  sterno-mastoid  areas 

External  carotid  artery 

Posterior  border'^' 
Sterno-mastoid  groove 

External  jugular  vein'' 

Fig.  108. — Parotid  Gland,  postero-medial  aspect. 

the  last  four  cerebral  nerves  by  the  posterior  belly  of  the 
digastric,  the  styloid  process  and  the  muscles  attached  to  it. 

The  medial  border  of  the  gland  lies  in  the  angle  between 
the  postero-medial  and  the  anterior  boundaries  of  the  parotid 
space,  where  the  styloid  process,  the  stylo-hyoid  muscle,  and 
the  posterior  belly  of  the  digastric  disappear  under  cover  of 
the  posterior  border  of  the  internal  pterygoid  muscle ;  and 
from  it  a  process,  the  pterygoid  iobe,  usually  projects  anteriorly, 
for  a  short  distance,  between  the  internal  pterygoid  and  the 
inner  surface  of  the  ramus  of  the  mandible.  Through  the 
base  of  this  process  the  external  carotid  passes  from  the 
postero-medial  to  the  antero-medial  surface  of  the  gland. 

The    Antero-medial    Surface.  —  The    medial    part    of   the 

II — 17  c 


264 


HEAD  AND  NECK 


antero-medial  surface  is  directed  anteriorly  and  lies  in  relation 
with  the  lower  part  of  the  posterior  border  of  the  internal 
pterygoid,  the  stylo-mandibular  ligament,  and  the  posterior 
border  of  the  ramus  of  the  mandible.  The  more  lateral  part  is 
directed  medially  and  rests  against  the  lateral  surface  of  the 
masseter.  This  surface  is  pierced  (i)  by  the  external  carotid 
artery,  (2)  the  posterior  facial  and  the  internal  maxillary  veins, 
(3)  all  the  terminal  branches  of  the  facial  nerve  except  the 
cervical,  and  (4)  by  the  duct  of  the  gland. 

As  the  dissector  examines  the  parotid  space  he  will  note 
that  as  the  external  carotid  disappears  under  cover  of  the 

Anterior  border 

of  upper  extremity^. 

Posterior  facial  vein 

Area  for  neck  of  mandible 

Transverse  facial  artery. 

Superficial  temporal  artery 
Internal  maxillary  artery 


Internal  maxillary  vein 
Anterior  border 


Posterior  facial  vein 


External  carotid  artery 


Fig.  109. — Parotid  Gland,  antero-medial  aspect. 


posterior  belly  of  the  digastric  it  is  placed  so  far  anteriorly 
that  it  is  also  under  cover  of  the  posterior  border  of  the 
mandible ;  and  it  does  not  emerge  from  under  cover  of  the 
mandible  until  it  reaches  the  level  of  the  neck  of  the  bone, 
where  it  appears  on  the  antero  -  medial  surface  of  the 
gland  and  divides  into  its  two  terminal  branches.  Further, 
he  will  now  readily  recognise  the  impossibility  of  studying 
the  upper  end  of  the  cervical  part  of  the  internal  carotid, 
the  upper  part  of  the  internal  jugular  vein,  and  the  last 
four  cerebral  nerves,  until  he  is  in  a  position  to  reflect  the 
posterior  belly  of  the  digastric  and  the  styloid  process ;  and 
as  both  of  them  are,  to  a  certain  extent,  under  cover  of  the 


TEMPORAL  AND  INFRATEMPORAL  REGIONS    265 

mandible  it  is  obvious  that  the  mandible  must  be  removed. 
This  will  be  done  during  the  dissection  of  the  temporal  and 
infratemporal  regions,  which  must  now  be  proceeded  with. 


TEMPORAL   AND   INFRATEMPORAL   REGIONS. 

Fascia  Temporalis.  —  The  temporal  fascia  is  a  strong 
glistening  membrane  which  is  stretched  over  the  temporal 
fossa,  binding  down  the  temporal  muscle.  Its  upper  margin 
is  attached  to  the  upper  of  the  two  curved  lines  which 
constitute  the  temporal  ridge  on  the  lateral  aspect  of  the 
skull,  and  anteriorly  to  the  temporal  line  of  the  frontal 
bone.  As  it  approaches  the  zygomatic  arch,  it  splits  into 
two  laminae,  which  are  separated  from  each  other  by  a  narrow 
interval  filled  with  fat.  The  two  laminae  are  attached  one  to 
the  upper  border  of  the  zygomatic  arch  and  the  posterior 
border  of  the  zygomatic  bone,  and  the  other  to  the  medial 
surfaces  of  these  two  portions  of  bone.  They  can  readily 
be  demonstrated  by  dividing  the  superficial  layer  close  to  its 
attachment,  and  throwing  it  upwards ;  by  the  handle  of  the 
knife  the  attachment  of  the  deep  layer  can  then  be  made  out. 
In  the  upper  part  of  its  extent,  the  temporal  fascia  is  com- 
paratively thin  and  the  fibres  of  the  subjacent  muscle  may 
be  seen  shining  through  it ;  below,  it  is  thicker,  and  owdng 
to  the  fat  which  is  interposed  between  its  laminae,  it  is 
perfectly  opaque.  It  is  pierced  immediately  above  the 
posterior  part  of  the  zygomatic  arch  by  the  middle  temporal 
branch  of  the  superficial  temporal  artery  and  by  the  middle 
temporal  vein  (p.  157). 

Musculus  Masseter. — The  masseter  is  a  massive  quadrate 
muscle  which  covers  the  ramus  of  the  mandible.  Its 
fibres  are  arranged  in  two  sets — a  superficial  and  a  deep. 
The  superficial  part  of  the  muscle  arises  from  the  anterior  two- 
thirds  of  the  lower  border  of  the  zygomatic  arch,  and  its 
fasciculi  are  directed  downwards  and  posteriorly.  The  deep 
/(^r/  springs  from  the  w^hole  length  of  the  medial  aspect  of  the 
zygomatic  arch,  and  also  from  the  posterior  third  of  its  lower 
border.  Its  fibres  proceed  downwards  and  anteriorly.  Only 
a  small  piece  of  the  upper  and  posterior  part  of  this  portion 
appears  on  the  surface.  The  masseter  is  inserted  into  the 
lateral  surface  of  the  ramus  of  the  mandible,  over  an  area 


266  HEAD  AND  NECK 

which  extends  downwards  to  the  angle,  and  upwards  so  as  to 
include  the  lateral  aspect  of  the  coronoid  process. 

Dissection.  —  To  display  the  temporal  muscle,  and  at  the  same  time 
expose  the  nerve  and  artery  of  supply  to  the  masseter,  make  the  following 
dissection.  Divide  the  deep  part  of  the  temporal  fascia  along  the  upper 
border  of  the  zygomatic  arch  and  remove  it.  The  middle  temporal  artery 
and  the  zygomatico-temporal  nerve,  which  pierce  it,  must  be  disengaged 
from  it  and  preserved.  The  zygomatic  arch,  with  the  attached  masseter, 
must  next  be  thrown  down  by  dividing  the  bony  arch  anterior  and  posterior 
to  the  origin  of  the  muscle.  First  make  use  of  the  saw,  and  then  complete 
the  division  by  means  of  the  bone  forceps.  The  posterior  cut  should  be 
made  immediately  anterior  to  the  mandibular  (O.T.  glenoid)  fossa  and 
the  head  of  the  lower  jaw  ;  the  anterior  cut  must  extend  obliquely  through 
the  zygomatic  bone,  from  the  extreme  anterior  end  of  the  upper  margin  of 
the  arch,  downwards  and  anteriorly  to  the  point  where  the  lower  margin 
meets  the  zygomatic  process  of  the  maxilla.  When  the  division  is  com- 
pleted, and  the  nerve  and  artery  to  the  masseter  are  divided,  the  whole 
arch  and  the  attached  masseter  may  be  readily  thrown  downwards  towards 
the  angle  of  the  mandible.  The  fleshy  origin  of  the  deep  portion  of 
the  masseter  from  the  medial  surface  of  the  zygomatic  arch  can  now  be 
seen.  The  dissection  is  frequently  complicated  by  a  number  of  fibres  from 
the  temporal  muscle  joining  this  part  of  the  masseter.  In  turning  the 
masseter  down,  its  nerve  and  artery  of  supply  must  first  be  cleaned  as 
they  pass  laterally  through  the  incisura  mandibulse  (O.T.  sigmoid  notch), 
posterior  to  the  tendon  of  the  temporal  muscle.  Leave  the  masseter 
attached  to  the  angle  of  the  jaw  and  clean  the  temporal  muscle. 

Musculus  Temporalis. — The  temporal  muscle  is  fan-shaped. 
It  arises  from  the  whole  extent  of  the  temporal  fossa,  from  the 
lower  of  the  two  lines  which  constitute  the  temporal  ridge  to 
the  infratemporal  crest  on  the  great  wing  of  the  sphenoid. 
It  receives  additional  fibres  also  from  the  deep  surface  of 
the  temporal  fascia.  From  this  broad  origin  the  fasciculi 
converge  towards  the  coronoid  process  of  the  mandible. 
The  anterior  fibres  descend  vertically,  the  posterior  fibres  at 
first  pursue  a  nearly  horizontal  course,  whilst  the  intermediate 
fasciculi  proceed  with  varying  degrees  of  obliquity.  As  it 
approaches  its  insertion,  a  tendon  is  developed  upon  its 
superficial  aspect,  and  this  is  inserted  into  the  summit  and 
anterior  edge  of  the  coronoid  process.  The  deep  part  of  the 
muscle  remains  fleshy,  and  gains  insertion  to  the  medial 
surface  of  the  same  bony  prominence  by  an  attachment  which 
reaches  as  low  down  as  the  point  where  the  anterior  margin  of 
the  ramus  merges  into  the  body  of  the  mandible.  The  inser- 
tion cannot  be  fully  examined  at  present ;  it  will  be  dealt  with 
later. 

Dissection. — Detach  the  coronoid  process  from  the  mandible,  and  turn 
it  upwards  with  the  attached  temporal  muscle.       A  very  oblique  cut  is 


TEMPORAL  AND  INFRATEMPORAL  REGIONS    267 

required  ;  it  should  extend  from  the  centre  of  the  incisura  above,  down- 
wards and  anteriorly,  to  the  point  where  the  anterior  margin  of  the  ramus 
meets  the  l:)ody  of  the  mandible.  First  use  the  saw,  and  then  complete 
the  division  with  the  bone  forceps.  The  buccinator  tierve  (O.T.  lottg  buccal) 
and  its  companion  artery  are  in  a  position  of  danger  during  this  dissection, 
and  must  be  carefully  guarded.  They  proceed  downwards  and  anteriorly 
under  cover  of  the  lower  part  of  the  temporal  muscle,  and  not  infrequently 
the  nerve  traverses  its  substance.  The  coronoid  process  and  the  temporal 
muscle  must  be  thrown  well  upwards,  and  the  muscular  fibres  separated, 
by  the  handle  of  the  knife,  from  the  bone  forming  the  lower  part  of  the 
temporal  fossa.  This  will  bring  into  view  the  deep  temporal  nef-ves  and 
artei-ies  as  they  ascend  between  the  cranial  wall  and  the  muscle.  This  is 
the  time  to  follow  the  middle  temporal  artejy  also.  It  will  be  noticed  to 
give  branches  to  the  muscle,  and  it  extends  upwards  upon  the  squamous  part 
of  the  temporal  bone.  The  zygomatico-temporal  nerve  also  should  be 
traced  to  the  point  where  it  emerges  from  the  minute  aperture  on  the 
temporal  surface  of  the  zygomatic  bone.  At  this  point  it  lies  under  cover 
of  the  temporal  muscle. 

The  infratemporal  region  (O.T.  pterygo-maxillary)  may  now  be  fully 
opened  up  by  removing  a  portion  of  the  ramus  of  the  mandible.  •  Two  hori- 
zontal cuts  must  be  made — one  through  the  neck  of  the  mandible,  and  the 
other  immediately  above  the  level  of  the  mandibular  (O.T.  inferior  dental) 
foramen.  To  find  the  level  of  the  foramen,  the  handle  of  the  knife  should  be 
thrust  between  the  ramus  and  the  subjacent  soft  parts,  and  carried  down- 
wards. Its  progress  will  soon  be  arrested  by  the  entrance  of  the  inferior 
alveolar  vessels  and  nerve  into  the  foramen,  and  the  lower  border  of  the 
instrument  will  correspond  with  the  line  along  which  the  bone  should  be 
cut.  Both  incisions  should  be  made  with  the  saw,  until  the  lateral  table 
of  the  bone  is  cut  through,  and  then  the  bone  forceps  may  be  employed  to 
complete  the  division. 

Parts  displayed  by  the  above  Dissection. — When  the  fat 
and  areolar  tissue  are  removed,  the  pterygoid  muscles  will 
come  into  view.  The  external  pterygoid  extends  horizontally 
to  the  neck  of  the  mandible.  The  internal  pterygoid,  embrac- 
ing the  anterior  part  of  the  external  pterygoid  muscle  between 
its  two  heads  of  origin,  proceeds  downwards  and  posteriorly 
upon  the  deep  surface  of  the  ramus  of  the  mandible.  It 
bears  very  much  the  same  relation  to  the  medial  aspect  of  the 
ramus  that  the  masseter  presents  to  its  lateral  surface.  The 
great  blood  vessel  of  the  space — the  internal  maxillary  artery 
— proceeds  anteriorly  upon  (frequently  under  cover  of)  the 
external  pterygoid  muscle.  The  nerves  of  the  region  also  will 
be  found  in  close  relationship  to  the  same  muscle.  Thus, 
emerging  from  between  its  upper  border  and  the  cranial  wall, 
at  the  level  of  the  infratemporal  crest,  are  the  masseteric  and 
the  two  deep  te?nporal  nerves ;  appearing  from  under  cover  of 
its  lower  border  are  the  inferior  alveolar  and  the  lifigital 
nerves;  whilst  the  aitriculo-temporal  nerve  is  related  to  its 
medial  surface  posteriorly  and  the  buccinator  nerve  anteriorly. 


268 


HEAD  AND  NECK 


The  former  appears  posterior  to  the  temporo-mandibular  joint, 
and  the  buccinator  nerve  either  pierces  it  or  emerges  from 
between  its  two  heads  of  origin.  The  spheno-ma7idibular 
ligament  also  will  be  seen.  It  is  the  thin  strip  of  membrane 
which  lies  medial  to  the  inferior  alveolar  nerve. 

Musculus  Pterygoideus  Extemus. — The  external  pterygoid 


Temporal  muscle 

Deep  temporal  artery- 


Deep  temporal  nerve 
Deep  temporal  artery 


Internal 
maxillary 
Posterior 
sup.  alveolar 
Buccinator 
nerve  and 
artery  '^^S 


Deep  temporal  nerve 
Masseteric  nerve 


Superficial  temporal  artery 
Auriculo-temporal  nerve 

External  pterygoid 
Middle  meningeal  artery 


Mastoid  process 
External  carotid 


Accessory  meningeal  artery 
Inferior  alveolar  artery 


Buccinator 


^Mylo-hyoid  artery  and  nerve 
^Inferior  alveolar  nerve 
Lingual  nerve 
Internal  pterygoid  muscle 


Fig.  no. — Dissection  of  the  Infratemporal  Region. 

arises  in  the  infratemporal  fossa  by  two  heads,  an  upper  and 
a  lower.  The  upper  head  springs  from  the  infratemporal 
ridge  and  surface  of  the  great  wing  of  the  sphenoid ;  the 
lower  head  takes  origin  from  the  lateral  surface  of  the  lateral 
pterygoid  lamina  (O.T.  external  pterygoid  plate).  The 
muscle  diminishes  in  width  as  it  passes  posteriorly,  and  it  is 
inserted  into  the  fovea  pterygoidea  on  the  anterior  surface 
of  the  neck  of  the  mandible,  and  also  into  the  anterior  margin 
of  the  discus  articularis  of  the  temporo-mandibular  articulation. 


TEMPORAL  AND  INFRATEMPORAL  REGIONS    269 

Musculus  Pterygoideus  Intemus. — The  internal  pterygoid 
also  is  bicipital  at  its  origin,  and  its  two  heads  embrace  the 
origin  of  the  lower  head  of  the  external  pterygoid.  The 
superficial  and  smaller  head  of  the  internal  pterygoid  springs 
from  the  lower  and  posterior  part  of  the  tuberosity  of  the 
maxilla,  and  also  from  the  lateral  surface  of  the  pyramidal 
process  (O.T.  tuberosity)  of  the  palate  bone ;  the  deep  head, 
hidden  by  the  external  pterygoid,  arises  in  the  pterygoid 
fossa  from  the  medial  surface  of  the  lateral  pterygoid  lamina, 
and  from  the  surface  of  the  pyramidal  process  of  the  palate 
bone  which  appears  between  the  two  pterygoid  laminae. 
The  two  heads  of  the  muscle  unite  at  the  lower  margin  of  the 
anterior  part  of  the  external  pterygoid,  and  the  fibres  proceed 
downwards  with  a  postero  -  lateral  inclination  and  gain 
insertion  into  the  angle  of  the  mandible,  and  into  the  lower 
and  posterior  part  of  the  medial  aspect  of  the  ramus  as 
high  as  the  mandibular  foramen. 

Arteria  Maxillaris  Interna. — This  vessel  is  the  larger  of 
the  two  terminal  branches  of  the  external  carotid  artery.  It 
takes  origin  immediately  posterior  to  the  neck  of  the 
mandible  and  proceeds  anteriorly  to  the  anterior  part  of  the 
infratemporal  fossa,  where  it  disappears  from  view  by  dipping 
between  the  two  heads  of  origin  of  the  external  pterygoid 
muscle  and  entering  the  pterygo-palatine  fossa.  It  is 
divided  into  three  parts  for  convenience  of  description.  The 
first  part  runs  horizontally  between  the  neck  of  the  mandible 
and  the  spheno-mandibular  ligament.  It  lies  along  the 
lower  border  of  the  posterior  part  of  the  external  pterygoid 
muscle,  and  usually  crosses  the  inferior  alveolar  nerve  super- 
ficially. The  second  part  extends  obliquely  upwards  and 
anteriorly  upon  the  lateral  surface  of  the  external  pterygoid 
muscle,  under  cover  of  the  insertion  of  the  temporal  muscle. 
The  third  part  dips  between  the  two  heads  of  the  external 
pterygoid  into  the  pterygo-palatine  fossa. 

This  is  the  most  frequent  arrangement,  but  it  is  not 
uncommon  to  find  the  second  part  of  the  artery  lying  in  a 
deeper  plane,  viz.  between  the  internal  and  external  pterygoid 
muscles.  In  that  case  the  vessel  makes  a  bend  laterally 
between  the  heads  of  the  external  pterygoid  muscle,  and 
appears  on  its  surface  before  entering  the  pterygo-palatine 
fossa. 

The  brafiches  of  the  internal  maxillary  artery  are  classified 


270 


HEAD  AND  NECK 


according  to  the  portion  of  the  vessel  from  which  they  spring. 
Only  one  branch  of  the  third  part,  viz.  the  posterior  superior 
alveolar  artery,  can  be  studied  in  this  dissection.  Those 
arising  from  the  first  and  second  parts  are : — 


From  the  First  Part. 

From  the  Second  Part. 

1.  Arteria  auricularis  profunda. 

2.  Arteria  tympanica. 

3.  Arteria  meningea  media. 

4.  Ramus  meningeus  accessorius. 

5.  Arteria  alveolaris  inferior. 

1.  Arteria  masseterica. 

2.  Rami  pterygoidei. 

3.  Arterice  temporales  profundse. 

4.  Arteria  buccinatoria. 

The  Deep  Auricular  Artery. — This  small  vessel  pierces 
the  anterior  wall  of  the  external  acustic  meatus  to  supply 
the  skin  which  lines  it,  and  also  the  superficial  part  of  the 
tympanic  membrane. 

The  Meningeal  and  Tympanic  Branches  proceed  upwards 
under  cover  of  the  external  pterygoid  muscle,  and,  therefore, 
cannot  be  fully  studied  until  that  muscle  is  reflected. 

The  Inferior  Alveolar  Artery  arises  opposite  the  middle 
meningeal,  and  runs  downwards,  upon  the  spheno-mandibular 
ligament,  to  enter  the  mandibular  foramen.  It  is  generally 
accompanied  by  two  venae  comites,  and  it  is  placed  posterior  to 
the  inferior  alveolar  nerve.  Just  before  entering  the  foramen, 
the  inferior  alveolar  artery  gives  off  the  slender  mylo-hyoid 
branch,  which  is  carried  downwards  and  anteriorly,  with  the 
corresponding  nerve,  upon  the  deep  aspect  of  the  mandible, 
to  the  digastric  triangle  of  the  neck. 

The  branches  from  the  second  part  are  given  off  for  the 
supply  of  the  neighbouring  muscles.  The  Masseteric  passes 
horizontally,  posterior  to  the  temporal  muscle,  with  the  nerve 
of  the  same  name,  and  has  been  seen  entering  the  masseter 
muscle.  The  Pterygoid  Branches  are  irregular  twigs  to  the 
pterygoid  muscles.  The  Deep  Temporal  Branches  are  two  in 
number — anterior  and  posterior;  they  pass  upwards  in  the 
temporal  fossa,  between  the  bony  wall  of  the  cranium  and  the 
temporal  muscle.  They  supply  twigs  to  the  temporal  muscle, 
and  they  anastomose  with  the  middle  temporal  artery.  The 
Buccinator  Branch  accompanies  the  buccinator  nerve,  and 
is   distributed    to    the    buccinator    muscle    and    the    mucous 


TEMPORAL  AND  INFRATEMPORAL  REGIONS    271 

membrane  of  the  cheek.  It  anastomoses  with  the  external 
maxillary  (O.T.  facial)  artery. 

The  Posterior  Superior  Alveolar  Branchy  from  the  third  part 
of  the  internal  maxillary  artery,  descends  upon  the  posterior 
aspect  of  the  maxilla,  and  sends  branches  through  the  alveolar 
canals  of  the  maxilla  for  the  supply  of  the  upper  molar 
and  prgemolar  teeth  (Fig.  no).  Some  small  twigs  go  to  the 
gum  and  others  supply  the  lining  membrane  of  the  maxillary 
sinus. 

Pterygoid  and  Internal  Maxillary  Veins. — The  veins  in 
this  region  are  very  numerous,  but  they  cannot  be  studied 
satisfactorily  in  an  ordinary  dissection.  They  constitute  a 
dense  plexus,  termed  the  pterygoid  plexus^  around  the  external 
pterygoid  muscle.  Tributaries  corresponding  to  the  branches 
of  the  internal  maxillary  artery  open  into  this  network, 
•whilst  the  blood  is  led  away  from  its  posterior  part  by  a  short 
wide  trunk,  called  the  internal  maxillary  vein.  This  vessel 
accompanies  the  first  part  of  the  internal  maxillary  artery 
into  the  parotid  gland,  and  joins  the  posterior  facial  vein 
behind  the  neck  of  the  mandible. 

The  pterygoid  venous  plexus  is  connected  with  the 
cavernous  sinus  by  an  emissary  vein.  It  communicates  with 
the  inferior  ophthalmic  vein,  through  the  inferior  orbital  fissure, 
and  with  the  anterior  facial  vein  by  an  anastomosing  channel 
called  the  deep  facial  vein  which  descends  across  the  external 
surface  of  the  buccinator  muscle. 

Articulatio  Mandibularis. — Before  the  external  pterygoid 
muscle  is  thrown  anteriorly,  the  temporo-mandibular  joint 
must  be  examined.  It  is  a  diarthrodial  joint  of  the  ginglymus 
type,  and  its  cavity  is  separated  into  an  upper  and  a  lower 
part  by  a  discus  articularis.  In  connection  with  it  there  are 
the  following  ligaments  : — 


Ligaments  Proper. 


1.  Capsule. 

2.  Temporo-mandibular. 


Accessory  Ligaments. 


1.  Spheno-mandibular. 

2.  Stylo-mandibular. 


Discus  Articularis. 


The  capsule  encloses  the  joint  cavity.     Above,  it  is  attached 
posteriorly,  laterally,  and  medially  to  the  margin  of  the   man- 


272 


HEAD  AND  NECK 


dibular  fossa,  and  anteriorly  to  the  anterior  margin  of  the 
articular  tubercle.  Below,  it  is  attached  to  the  neck  of  the 
mandible ;  and  between  its  upper  and  lower  attachments  it  is 
connected  with  the  margins  of  the  discus  articularis. 

The  temporo-mandibular  ligament  (O.T.  external  lateral)  is 
a  strong  triangular  band  which  is  attached  above  to  the 
lateral  surface  of  the  posterior  part  of  the  zygoma  and  to  the 
tubercle  at  the  root  of  the  zygoma.  Its  fibres  run  down- 
wards and  posteriorly  to  the  neck  of  the  mandible. 

The  spheno-fnandibular  ligament  (O.T.  internal  lateral)  is  a 
long  membranous  band  which  extends  from  the  spine  of  the 
sphenoid  to  the  lingula  and  to  the  sharp  medial  margin  of  the 


Tuberculuni  articulare 


Upper  joint  cavity 
Discus  articularis 
Lower  joint  cavity     \ 
Capsule  \       \ 


/ 
Mastoid  process 


Styloid  process 


Fig.  III. — Section  through  Temporo-mandibular  Joint, 

mandibular  foramen.  It  is  not  in  direct  relationship  with  the 
joint.  Above,  it  lies  medial  to  the  external  pterygoid  muscle 
and  the  auriculo-temporal  nerve ;  lower  down,  the  internal 
maxillary  vessels  intervene  between  it  and  the  neck  of  the 
mandible ;  whilst,  still  lower,  the  inferior  alveolar  vessels  and 
nerve  are  interposed  between  it  and  the  ramus  of  the  mandible. 

The  stylo-mandibular  ligament  has  been  noticed  already.  It 
is  a  fibrous  band,  derived  from  that  portion  of  the  deep 
cervical  fascia  which  forms  a  part  of  the  capsule  of  the 
parotid  gland.  It  is  attached  above  to  the  styloid  process, 
and  below  to  the  angle  and  posterior  border  of  the  ramus  of 
the  mandible,  between  the  internal  pterygoid  and  masseter 
muscles. 

An   examination  of  these   ligaments  will   show  that  very 


TEMPORAL  AND  INFRATEMPORAL  REGIONS    273 


little  is  added  to  the  strength  of  the  joint  by  their  presence. 
The  security  of  the  joint  depends  not  so  much  upon  its  liga- 
ments as  upon  the  strong  muscles  of  mastication,  which  keep 
the  head  of  the  mandible  in  its  place. 

The  discus  articularis  is  an  oval  plate  of  fibro-cartilage,  with 
its  long  axis  directed  transversely.  It  is  interposed  between 
the  condyle  of  the  mandible  below  and  the  mandibular  fossa 
(O.T.  glenoid)  and  the  articular  tubercle  (O.T.  eminentia 
articularis)  above,  and  it  divides  the  joint  cavity  into  upper 
and  lower  parts,  each  of  which  is  provided  with  a  separate 
synovial  lining.  To  expose  the  cartilage,  the  temporo-man- 
dibular  ligament  must  be  removed.  The  disc  will  then  be 
seen  to  be  adapted  to  the 
two  bony  surfaces  between 
which  it  lies.  Above,  it  is 
concavo  -  convex  in  corre- 
spondence with  the  tuber- 
culum  articulare  and  the 
mandibular  fossa  of  the  tem- 
poral bone ;  whilst  below,  it 
is  concave,  and  fits  upon 
the  upper  aspect  of  the  con- 
dyle of  the  mandible.  In 
the  centre  it  is  thin,  and  in 
some  cases  it  is  perforated. 
Its  circumference  is  thick, 
more  especially  posteriorly. 
It  should  be  noted  also  that 
the  external  pterygoid  muscle  is  partly  inserted  into  its 
anterior  border. 

The  syfiovial  stratum  which  lines  the  capsule  enclosing  the 
upper  cavity  of  the  joint  is  of  greater  extent  and  looser  than 
that  of  the  lower  compartment.  This  is  in  association  with 
the  larger  size  of  the  articular  surface  of  the  temporal  bone 
as  contrasted  with  the  condylar  surface. 

Movements.  —  The  movements  which  the  mandible  can  perform  at 
the  temporo- mandibular  joint  are  the  following:  —  (i)  depression;  (2) 
elevation  ;  (3)  protraction  ;  (4)  retraction  ;  (5)  lateral  or  chewing  move- 
ments. When  the  mandible  is  depressed  the  discus  articularis  and  the 
condyle  move  anteriorly  on  the  mandibular  fossa,  and  the  condyle  finally 
takes  up  a  position  on  the  tuberculum  articulare.  This  forward  gliding 
of  the  disc  and  condyle  in  the  upper  compartment  of  the  joint  is  accom- 
panied by   another  movement   in  the   lower   compartment    of  the  joint, 

VOL.  II — 18 


Fig.  112. — Diagram  of  the  different 
positions  occupied  by  the  head  of  the 
mandible  and  the  discus  articularis 
as  the  mouth  is  opened  and  closed. 


2  74  HEAD  AND  NECK 

which  consists  in  a  rotation  of  the  condyle  of  the  mandible  on  the 
lower  surface  of  the  articular  disc.  Elevation  of  the  mandible  or  closure 
of  the  mouth  is  brought  about  by  a  reverse  series  of  changes  in  both 
compartments  of  the  joint.  Whilst  these  movements  are  going  on,  the 
mandible  rotates  around  a  transverse  axis  which  traverses  the  bone  in 
the  neighbourhood  of  the  mandibular  foramen.  This  is  the  point,  there- 
fore, of  least  movement,  and  consequently  in  opening  and  shutting  the 
mouth  the  inferior  alveolar  vessels  and  nerves  are  not  unduly  stretched. 
In  protraction  and  retraction  the  movement  is  chiefly  confined  to  the 
upper  compartment  of  the  joint,  and  the  condyle  of  the  mandible  with 
the  articular  disc  glides  anteriorly  and  posteriorly  upon  the  temporal 
articular  surface.  In  the  lateral  movements  of  the  jaw  the  mandible  is 
carried  alternately  from  side  to  side,  as  in  the  process  of  chewing. 

The  muscles  on  each  side  which  are  chiefly  engaged  in  producing  these 
movements  are  the  following: — (i)  depressors— \\\q  platysma,  the  mylo- 
hyoid, and  the  anterior  belly  of  the  digastric  ;  (2)  elevators — the  masseter, 
internal  pterygoid,  temporal ;  (3)  protractors — the  external  pterygoid,  and 
to  some  extent  the  internal  pterygoid  and  the  superficial  fibres  of  the 
masseter  ;  (4)  retractor — the  posterior  fibres  of  the  temporal  and  the  deep 
fibres  of  masseter  ;  (5)  lateral  movement  is  produced  by  the  muscles  of 
opposite  sides  acting  alternately. 

Reflection  of  External  Pterygoid. — The  condyle  of  the  mandible  must 
now  be  disarticulated  and  thrown  anteriorly  with  the  attached  external 
pterygoid  muscle.  It  is  well  to  detach  the  discus  articularis  with  the 
head  of  the  bone,  in  order  that  it  may  be  more  thoroughly  examined. 
Care  must  be  taken  not  to  injure  the  auriculo-temporal  nerve,  which  lies 
in  close  proximity  to  the  medial  aspect  of  the  joint.  When  the  dis- 
articulation is  complete,  the  muscle  may  be  displaced  anteriorly  by  gently 
pushing  the  condyle  under  the  internal  maxillary  artery. 

The  reflection  of  the  external  pterygoid  muscle  brings  into  view,  after 
a  little  dissection,  the  mandibular  division  of  the  trigeminal  7ierve, 
emerging  from  the  foramen  ovale,  and  breaking  up  into  its  branches  of 
distribution.  The  slender  chorda  tympani  will  be  found  proceeding  down- 
wards and  anteriorly  to  join  the  lingual  nerve  ;  and  the  middle  meningeal, 
tympanic,  and  accessory  meningeal  arteries  may  be  traced  to  the  points 
where  they  leave  the  infratemporal  region. 

Arterise  Meningea  Media  et  Tympanica  and  Ramus  Menin- 
geus  Accessorius. — The  middle  meningeal  artery  has  already 
been  seen  arising  from  the  first  part  of  the  internal  maxillary 
artery.  It  proceeds  upwards,  medial  to  the  external  ptery- 
goid muscle  and  lateral  to  the  tensor  palati,  and  disappears 
from  view  through  the  foramen  spinosum,  by  which  it  enters 
the  cranial  cavity  (p.  212).  It  is  usually  embraced  by  the 
two  roots  of  the  auriculo-temporal  nerve. 

The  accessory  meningeal  artery  and  the  tyjjipanic  artery  generally  arise 
from  the  middle  meningeal.  The  accessory  meningeal  inclines  anteriorly  and 
upwards,  and  enters  the  cranial  cavity  by  passing  through  the  foramen 
ovale ;  the  tympanic  runs  upwards  and  posteriorly,  and  reaches  the  , 
tympanum  by  passing  through  the  petro-tympanic  fissure  (O.T.  Glaserian). 
In  the  tympanic  cavity  it  anastomoses  with  the  styloid-mastoid  branch  of 
the  posterior  auricular  artery. 


TEMPORAL  AND  INFRATEMPORAL  REGIONS    275 


Nervus  Mandibularis. — The  mandibular  branch  of  the 
tricreminal  nerve  arises  within  the  cranium  from  the  semilunar 
(O^T.  Gasserian)  ganglion,  and  enters  the  infratemporal 
region  through  the  foramen  ovale.  It  is  composed  of 
sensory  fibres,  but  it  is  accompanied  through  the  foramen 
by  the  small  77iotor  root  of  the  trigeminal  nerve ;  and  by  the 
union  of  the  sensory  and  motor  parts,  immediately  after 
they  gain  the  exterior  of  the  cranium,   a  7nixed  7ierve-trunk 


Facial  nerve 


Tympanic  plexus 


Tj'mpanic  branch  of 
glosso-pharj'ngeal 


Chorda  tympani . . 

Auriculo-temporal  ' 
Inferior  alveolar  nerve 


Stylo-glossus 
Mylo-hyoid  nerve 


Anterior  deep  temporal 
Buccinator  nerve 


Mj'lo-hyoid  muscle  '' 
Branches  of  mj-lo-hyoid  nerve 


Communication  to  hypoglossal 

Submaxillary  ganglion 

H5'oglossus 

—  Genio-glossus 


Mental  branch 
Incisive  branch 
Digastric 


Fig.  113. — Diagram  of  Mandibular  Nerve.      By  Prof.  A.  M.  Paterson. 


1.  Ganglion  geniculi 

2.  Carotico-tympanic  nerve 

3.  Small  superficial  petrosal  nerve 

4.  Internal  carotid  artery 

5.  Middle  meningeal  artery 

6.  Symp.  root  of  otic  ganglion 


7.  Otic  ganglion 

8.  Nerve  to  tensor  tympani 

9.  Nerve  to  tensor  palati 

10.  Nerve  to  internal  pterj'goid 

11.  Mandibular  nerve  trunk 

12.  Anterior  division 


13.  Masseteric   and    post,    deep 

temporal 

14.  Lingual  nerve 

■'I'    \  Pterj'goid  branches 


results.  This  nerve-trunk  lies  medial  to  the  external  pterygoid 
muscle  and  lateral  to  the  tensor  palati,  and  after  a  very  short 
course  (not  exceeding  5  mm.)  it  ends  by  dividing  into 
two  parts,  named  the  anterior  and  posterior  divisio?is  of  the 
mandibular  nerve  (Fig.  113). 

The  trunk  of  the  mandibular  nerve  gives  off  two  branches 
before  it  divides,  viz.,  (i)  nervus  spi?iosus  (O.T.  recurrent  7iej-ve\ 
and  (2)  the  nerve  to  the  internal  pterygoid  muscle. 

The   7iervus  spinosus  is  a  very  slender  twng  which  enters 

II— 18  a 


2  76  HEAD  AND  NECK 

the  cranium  by  accompanying  the  middle  meningeal  artery 
through  the  foramen  spinosum.      It  supplies  the  dura  mater. 

The  nerve  to  the  internal  pterygoid  will  be  found  passing 
under  cover  of  the  posterior  border  of  the  internal  pterygoid 
muscle  at  its  upper  end.  In  close  relation  to  the  root  of 
this  nerve  is  the  otic  ganglion. 

From  the  two  terminal  divisions  of  the  mandibular 
trunk  the  chief  branches  of  distribution  arise.  The  anterior 
division  is  much  the  smaller  of  the  two,  and  is  composed  almost 
entirely  of  motor  fibres  derived  from  the  motor  root  of  the 
trigeminal  nerve.  The  only  sensory  fibres  which  it  contains 
are  those  which  form  the  buccinator  nerve.  It  gives  off  the 
following  branches : — 


1.  Masseteric. 

2.  Two  deep  temporal. 


3.  External  pterygoid. 

4.  Buccinator. 


The  large  posterior  division  is  chiefly  sensory.  It  contains 
only  a  very  few  fibres  from  the  motor  root,  and  these  are 
prolonged  into  its  inferior  alveolar  branch,  and  afterwards 
come  off  in  the  form  of  the  mylo-hyoid  nerve.  The  branches 
of  the  posterior  division  are:  (i)  auriculo-temporal ;  (2) 
inferior  alveolar  ;  (3)  lingual. 

Nervus  Massetericus. — The  masseteric  nerve  runs  hori- 
zontally above  the  external  pterygoid  muscle,  and,  passing 
through  the  incisura  mandibulae  (O.T.  sigmoid  notch) 
posterior  to  the  temporal  muscle,  it  enters  the  posterior  and 
upper  part  of  the  deep  surface  of  the  masseter.  Before 
reaching  the  masseter  it  gives  one  or  two  twigs  to  the 
temporo-mandibular  joint. 

Nervi  Temporales  Profundi.  —  There  are  usually  two 
deep  temporal  nerves,  anterior  and  posterior.  The  posterior 
nerve  is  the  smaller  of  the  two ;  it  frequently  arises  by  a 
common  root  with  the  masseteric.  Both  deep  temporal 
nerves  pass  laterally  above  the  external  pterygoid,  and  then 
turn  upward  on  the  medial  wall  of  the  temporal  fossa.  They 
supply  the  temporal  muscle. 

Nervus  Buccinatorius. — The  buccinator  nerve  (O.T.  long 
buccal)  is  the  largest  of  the  branches  arising  from  the 
anterior  division  of  the  mandibular  nerve.  It  proceeds 
laterally  between  the  two  heads  of  the  external  pterygoid 
muscle,  and  then  runs  downwards  and  anteriorly  under 
cover  of  the  temporal  muscle,  and  under  cover  of  the  anterior 


TEMPORAL  AND  INFRATEMPORAL  REGIONS    277 

border  of  the  masseter  also,  to  reach  the  outer  surface  of  the 
buccinator  muscle.  There  it  unites  with  branches  of  the 
facial  nerve  to  form  the  buccal  plexus^  from  which  branches  are 
distributed  to  the  mucous  membrane  and  skin  of  the  cheek. 

The  buccinator  nerve  is  a  sensory  nerve,  and  all  the  sensory 
fibres    in    the    anterior    division    of    the    mandibular    nerve 
enter  into   its   composition.     A  few   motor  fibres,    however, 
are  also  prolonged  into  it ;  these  come   off  from  it   in  two 
branches,    viz.,    (i)    in   the   nerve   to    the    external  pterygoid^ 
which,  as  a  rule,  arises  in  common  with  the  buccinator  nerve  ; 
and  (2)  in  a  third  twig  of  supply  to  the  temporal  muscle.     This 
te7nporal  branch  springs  from  the  buccinator  nerve,  after  it  has 
reached   the  lateral  surface   of   the    external   pterygoid,   and 
proceeds  upwards  to  supply  the  anterior  part  of  the  temporal 
muscle    (Fig.    no).       In    some   cases  the    buccinator  nerve 
pierces  the  temporal  muscle  instead  of  passing  under  cover  of  it. 
Nervus    Auriculo  -  Temporalis.  — The    auriculo  -  temporal 
nerve  springs   by  two  roots  from    the   posterior   division   of 
the  mandibular  nerve,  under  cover  of  the  external  pterygoid. 
The    two   roots  are   composed   of   sensory   fibres    and    each 
receives  a  communication  from  the  otic  ganglion,  by  means  of 
which  it  is  brought  indirectly  into  association  with  the  glosso- 
pharyngeal nerve.     The  roots  embrace  the  middle  meningeal 
artery,  and  unite  posterior  to  it  to  form  a  stem  which  runs 
posteriorly    between    the    neck    of    the    mandible    and    the 
spheno-mandibular  ligament.     At  the  interval  between  the  ear 
and  mandible  it  turns  upwards,  in  relation  to  the  deep  surface 
of  the  parotid  gland,  crosses  the  zygoma  in   company  with 
the  superficial  temporal  artery,  and  enters  the  scalp,  where  it 
breaks  up  into  terminal  branches. 

Its  branches  are:  (i)  one  or  two  strong  branches  of 
communication  to  the  temporo-facial  nerve;  (2)  a  few  slender 
filaments  which  enter  the  posterior  aspect  of  the  temporo- 
mandibular joint ;  (3)  some  twigs  to  the  parotid  gland ;  (4) 
terminal  filaments  to  the  skin  over  the  temporal  region  and 
summit  of  the  head  ;  (5)  auricular  branches. 

The  auricular  branches  are  usually  two  to  the  skin  lining 
the  interior  of  the  external  meatus,  and  two  to  the  integument 
over  the  upper  and  anterior  part  of  the  auricle.  The  former 
gain  the  interior  of  the  meatus  by  passing  between  the  osseous 
and  cartilaginous  portions  of  the  canal. 

Nervus  Alveolaris  Inferior. — The  inferior  alveolar  nerve 
n— 18  h 


278  HEAD  AND  NECK 

(O.T.  inferior  dental)  is  the  largest  branch  of  the  mandibular 
nerve.  Emerging  from  under  cover  of  the  external  pterygoid, 
at  the  lower  border  of  the  muscle,  it  passes  downwards  upon 
the  spheno-mandibular  ligament  and  enters  the  mandibular 
foramen.  The  inferior  alveolar  artery  runs  downwards 
posterior  to  it,  whilst  the  lingual  nerve  is  anterior  to  it 
and  upon  a  somewhat  deeper  plane.  The  inferior  alveolar 
is  a  sensory  nerve,  but  a  few  fibres  from  the  motor  root 
are  prolonged  downwards  within  its  sheath  as  far  as  the 
mandibular  foramen.  At  this  point  they  come  off  as  the 
slender  mylo-hyoid  nerve. 

The  mylo-hyoid  nerve,  accompanied  by  the  artery  of  the 
same  name,  pierces  the  spheno-mandibular  ligament  and 
proceeds  downwards  and  anteriorly  in  a  groove  upon  the 
inner  surface  of  the  mandible  to  the  digastric  triangle.  A 
narrow  prolongation  of  the  spheno  -  mandibular  ligament 
bridges  over  the  groove  and  holds  the  nerve  and  vessel  in 
position.  In  the  digastric  triangle  the  mylo-hyoid  nerve  has 
been  dissected  already  (p.  230).  It  breaks  up  into  numerous 
branches  for  the  supply  of  two  muscles,  viz.,  (i)  the  mylo- 
hyoid, and  (2)  the  anterior  belly  of  the  digastric. 

Nervus  Lingualis. — The  lingual  nerve  is  entirely  sensory. 
In  the  first  part  of  its  course,  like  the  other  branches  of  the 
mandibular  nerve,  it  lies  medial  to  the  external  pterygoid 
muscle.  As  it  descends  it  appears  at  the  lower  border  of 
the  muscle.  Then  it  proceeds  downwards  and  anteriorly, 
between  the  internal  pterygoid  muscle  and  the  mandible,  and 
enters  the  submaxillary  region,  where  it  will  afterwards  be 
traced  to  the  tongue.  It  lies  anterior  to  and  on  a  slightly 
deeper  plane  than  the  inferior  alveolar  nerve.  It  gives  off 
no  branches  in  the  infratemporal  region,  but,  whilst  still 
under  cover  of  the  external  pterygoid,  it  is  joined  at  an  acute 
angle  by  the  chorda  tympani  branch  of  the  facial  nerve.  Not 
infrequently,  also,  a  communicating  twig  passes  between  it 
and  the  inferior  alveolar  nerve. 

Chorda  Tympani. — This  is  a  slender  nerve  which  arises 
from  the  facial  in  the  canalis  nervi  facialis  (O.T.  aqueduct  of 
Fallopius).  It  gains  the  infratemporal  region  by  traversing 
the  tympanic  cavity  and  appearing  through  the  medial  part 
of  the  petro-tym  panic  fissure  (O.T.  Glaserian),  whence  it  runs 
downwards  and  anteriorly,  medial  to  the  spheno-mandibular 
ligament.     It  is  joined  by  a  slender  filament  from  the  otic 


SUBMAXILLARY  REGION  279 

ganglion,  and  it  unites  with  the  lingual  nerve  a  short  distance 
below  the  upper  end  of  the  latter. 

Dissection. — The  student  should  now  endeavour,  by  means  of  a  Key's 
saw,  a  chisel,  and  the  bone  forceps,  to  remove  the  outer  table  of  the  mandible, 
and  thus  open  up  the  mandibular  canal. 

Structures  within  the  Mandibular  Canal. — The  mandibular 
canal  is  traversed  by  the  inferior  alveolar  vessels  and  nerve, 
which  give  off  twigs  to  the  roots  of  the  molar  and  praemolar 
teeth.  Both  the  artery  and  the  nerve  terminate  by  dividing 
into  a  mental  and  incisor  branch. 

The  mental  artery  and  nerve  appear  on  the  face  through 
,the  mental  foramen,  and  have  been  examined  already;  the 
incisor  artery  and  nerve  pass  anteriorly  to  the  symphysis  and 
send  up  twigs  to  the  canine  and  incisor  teeth.  The  vessel 
anastomoses  in  the  bone  with  the  corresponding  artery  of 
the  opposite  side. 


SUBMAXILLARY  REGION. 

The  superficial  area  of  the  submaxillary  region  has  been 
dissected  already,  under  the  name  of  the  anterior  part  of  the 
digastric  triangle  (p.  230).  It  is  now  necessary  to  carry  the 
dissection  to  a  deeper  plane,  in  order  to  expose  a  number 
of  parts  in  connection  with  the  tongue  and  floor  of  the 
mouth.     The  structures  thus  displayed  are  : — 

1.  Submaxillary  gland  and  its  duct. 

2.  Sublingual  gland. 

3.  Side  of  the  tongue,  and  the  mucous  membrane  of  the  mouth. 

(  Mylo-hyoid. 
Digastric. 
Stylo-hyoid. 

4.  Muscles.     \   Hyoglossus. 
Stylo-glossus. 
Genio-hyoid. 
Genio-glossus. 

(  Mylo-hyoid. 
Hypoglossal. 

5.  Nerves.       X   Lingual. 

1,  Glosso-pharyngeal. 

6.  Submaxillary  ganglion. 

7.  Lingual  artery  and  veins. 

8.  Part  of  the  external  maxillary  artery. 

9.  Stylo-hyoid  ligament. 

Dissection.— To  prepare  the  part  for  dissection,  it  is  necessary  to  throw 
back  the  head  to  its  full  extent,  and  turn  it  slightly  to  the  opposite  side. 
II— 18  c 


28o  HEAD  AND  NECK 

If  the  stuffing  in  the  mouth  has  not  been  previously  removed,  it  should 
be  taken  out  now.  When  this  has  been  done,  divide  the  external  maxillary 
artery  and  the  anterior  facial  vein  at  the  point  where  they  cross  the  lower 
border  of  the  mandible.  Next  detach  the  anterior  belly  of  the  digastric  from 
its  attachment  to  the  anterior  part  of  the  medial  aspect  of  the  lower  border 
of  the  mandible  ;  and  then,  with  the  saw,  cut  through  the  mandible  lateral 
to  the  median  plane.  ^  It  is  essential  that  the  division  of  the  anterior  part 
of  the  mandible  should  be  slightly  lateral  to  the  median  plane  on  each 
side,  in  order  that  the  median  part  of  the  bone,  with  the  attachments 
of  the  genioid  muscles,  may  be  left  intact. 

After  the  division  of  the  bone  has  been  completed  the  lower  border  of 
the  lateral  part  of  the  mandible  must  be  everted,  turned  slightly  upwards, 
and  fixed  in  position  with  hooks.  When  this  has  been  done  the  boundaries 
and  contents  of  the  submaxillary  region  can  be  examined. 

Part  of  the  region  has  already  been  seen  as  the  digastric  portion  of  the 
anterior  triangle  of  the  neck,  but  it  will  now  be  obvious  that  the  region 
occupied  by  the  submaxillary  gland  is  much  more  extensive  than  the 
digastric  triangle  ;  for,  although  both  are  bounded  anteriorly  and  posteriorly 
by  the  anterior  and  posterior  bellies  of  the  digastric  muscle,  the  upper 
boundary  of  the  digastric  triangle  is  the  lower  border  of  the  mandible, 
whilst  the  submaxillary  region  extends  upwards  to  the  level  of  the  mylo- 
hyoid ridge  on  the  inner  surface  of  the  mandible. 

After  the  mandible  has  been  turned  upwards  the  dissector  should 
proceed,  in  the  first  place,  to  exam.ine  the  relations  of  the  digastric  and 
stylo-hyoid  muscles,  then  the  mylo-hyoid  muscle,  and  afterwards  he  must 
study  the  submaxillary  and  sublingual  glands  and  the  deeper  structures 
which  are  found  in  the  medial  boundary  of  the  submaxillary  region. 

Musculus  Digastricus. — This  muscle  limits  the  sub- 
maxillary region  inferiorly  and  separates  it  from  the  carotid 
and  submental  triangles. 

The  anterior  belly  of  the  digastric  springs  from  the  inner 
surface  of  the  lower  border  of  the  mandible  close  to  the 
symphysis ;  and  the  posterior  belly  arises  from  the  mastoid 
notch  of  the  temporal  bone  on  the  medial  side  of  the  mastoid 
process.  The  two  bellies  converge  upon  the  upper  border  of 
the  hyoid  bone,  where  they  are  united  by  an  intermediate 
tendon,  which  is  attached  to  the  hyoid  bone  at  the  junction 
of  the  body  with  the  great  cornu,  by  a  strong  loop  of  fibrous 
tissue  developed  from  the  deep  cervical  fascia.  Posterior  to 
the  loop,  through  which  it  plays,  the  intermediate  tendon 
passes  through  the  cleft  lower  end  of  the  stylo-hyoid  muscle. 

Relations. — The  anterior  belly  is  covered  by  the  skin, 
superficial  fascia  and  the  platysma,  and  the  deep  fascia.  It 
is  overlapped  by  the  anterior  border  of  the  submaxillary  gland, 
and  its  deep  surface  is  in  contact  with  the  mylo-hyoid  muscle. 
Its  anterior  border  is  the  posterior  boundary  of  the  submental 

^  If  the  part  is  soft  and  pliable  there  may  be  no  necessity  to  make  this 
division  of  the  bone. 


SUBMAXILLARY  REGION  281 

triangle,  and  its  posterior  border  is  the  anterior  boundary  of 
tlie  digastric  triangle. 

The  relations  of  the  posterior  belly  are  more  numerous 
and  important.  Posteriorly,  it  is  covered  by  the  mastoid 
process  and  the  attachments  of  the  sterno -mastoid  and 
splenius  capitis  muscles.  Between  the  mastoid  process  and 
the  angle  of  the  mandible  it  forms  part  of  the  postero-medial 
boundary  of  the  parotid  space  and  is  covered  by  the  parotid 
gland ;  next  it  is  covered  by  the  angle  of  the  mandible  and 
the  insertion  of  the  internal  pterygoid  muscle.  As  it  lies  in 
the  anterior  triangle  it  is  covered  by  the  skin,  the  superficial 
fascia  and  platysma,  and  the  deep  fascia ;  it  is  crossed  by 
the  anterior  facial  vein,  and  is  overlapped  by  the  posterior 
part  of  the  submaxillary  gland. 

It  is  superficial  to  the  internal  jugular  vein,  the  internal 
and  the  external  carotid  arteries,  the  external  maxillary  artery, 
the  middle  constrictor  of  the  pharynx,  and  the  lower  and 
posterior  part  of  the  hyoglossus  muscle.  The  accessory 
nerve  passes  posteriorly  and  downwards  between  it  and  the 
internal  jugular  vein,  and  the  occipital  artery  passes  upwards 
and  posteriorly  under  cover  of  its  lower  border,  superficial 
to  the  accessory  nerve.  The  hypoglossal  nerve  descends 
vertically  on  its  deep  surface  in  the  angle  between  the 
internal  jugular  vein  and  the  internal  carotid  artery,  and 
the  glosso-pharyngeal  nerve  passes  anteriorly  and  downwards 
between  it  and  the  internal  carotid.  The  posterior  auricular 
artery  runs  upwards  and  posteriorly  along  the  posterior  part 
of  its  upper  border  under  cover  of  the  postero-medial  surface 
of  the  parotid,  and  the  stylo-hyoid  muscle  descends  along  the 
same  border. 

The  posterior  belly  is  supplied  by  the  facial  nerve,  and  the 
anterior  belly  by  the  mylo-hyoid  branch  of  the  inferior  alveolar 
nerve. 

Musculus  Stylohyoideus. — The  stylo-hyoid  muscle  is  a 
small  muscular  bundle  which  springs  from  the  posterior 
border  and  lateral  surface  of  the  middle  third  of  the  styloid 
process  and  descends  along  the  upper  border  of  the  posterior 
belly  of  the  digastric.  It  divides  below  into  two  slips  which 
embrace  the  intermediate  tendon  of  the  digastric  and  are  then 
inserted  into  the  hyoid  bone,  at  the  junction  of  the  great 
cornu  with  the  body.  Its  main  relations  are  practically  the 
same  as  those  of  the  posterior  belly  of  the  digastric,  but  it  is 


2«2 


HEAD  AND  NECK 


not  under  cover  of  the  mastoid  process,  the  sterno-mastoid, 
and  the  splenius  muscles.     It  is  supplied  by  \\\^  facial  nerve. 

Dissection. — Turn  the  anterior  part  of  the  submaxillary  gland  posteriorly, 
and  clean  the  posterior  part  of  the  mylo-hyoid  muscle,  which  lies  deep  to 
it.  Note  that  a  process,  the  deep  part  of  the  gland,  springs  from  the 
medial  surface  of  the  superficial  part  and  passes  anteriorly,  deep  to  the 
mylo-hyoid.  Dissect  the  external  maxillary  artery  out  of  the  deep  sulcus  in 
the  posterior  part  of  the  gland,  without  injuring  its  submental  branch 
which  runs  anteriorly  along  the  lower  border  of  the  mandible  ;  then  displace 
the  posterior  part  of  the  gland  anteriorly  and  expose  the  hypoglossal  nerve 
immediately  above  the  great  cornu  of  the  hyoid  bone,  and,  at  a  higher 
level,  the  lingual  nerve.  Both  nerves  lie  on  the  lateral  surface  of  the 
hyogiossus  muscle.  Hanging  from  the  lower  border  of  the  lingual  nerve  is 
the  small  submaxillary  ganglion,  from  which  several  branches  pass  to  the 
gland.  Note  again  the  deep  part  of  the  gland,  springing  from  the  medial 
surface  of  the  superficial  part,  and  also  the  duct  of  the  gland  emerging 
from  the  superficial  part  of  the  gland  and  passing  anteriorly,  with  the 
deep  part,  between  the  mylo-hyoid  muscle  laterally  and  the  hyo-glossus 
medially.  Then  study  the  position  and  relations  of  the  superficial  portion 
of  the  gland.  The  relations  of  the  deep  part  will  be  seen  after  the  mylo- 
hyoid is  reflected. 

Glandula  Submaxillaris. — The  submaxillary  salivary  gland 
consists  of  a  superficial  larger  portion  and  a  deep  smaller 
portion.  The  superficial  portion  is  lodged  in  a  space  which 
is  bounded  anteriorly  by  the  anterior  belly  of  the  digastric ; 
posteriorly  by  the  posterior  belly  of  the  digastric,  the  stylo-hyoid, 
and  the  stylo-mandibular  ligament ;  below  by  the  deep  fascia 
of  the  neck ;  and  laterally  by  the  inner  surface  of  the  body 
of  the  mandible  and  the  lower  part  of  the  medial  surface  of 
the  internal  pterygoid  muscle.  The  fascial  relations  of  the 
gland  have  been  described  already  (p.  226).  The  dissector 
should  note  now  that,  in  accordance  with  the  contour  of  the 
space  in  which  it  lies,  he  can  recognise  that  the  superficial 
part  of  the  gland  possesses  an  anterior  and  a  posterior 
extremity,  and  three  more  or  less  well-defined  surfaces, 
inferior,  lateral,  and  medial.  The  posterior  extremity  abuts 
against  the  stylo-mandibular  ligament,  which  separates  it  from 
the  parotid,  and  it  overlaps  the  stylo-hyoid  and  posterior 
belly  of  the  digastric.  It  is  cleft  by  a  groove  in  which 
lies  the  external  maxillary  artery.  The  anterior  extremity 
rests  on  the  anterior  belly  of  the  digastric. 

The  inferior  surface  is  covered  by  the  layer  of  deep 
cervical  fascia  which  extends  upwards  from  the  great  cornu 
of  the  hyoid  bone  to  the  lower  border  of  the  mandible ;  it 
is  crossed  posteriorly,  under  cover  of  the  deep  fascia,  by  the 


SUBMAXILLARY  REGION 


283 


anterior  facial  vein.  Along  its  upper  border  lie  the  majority 
of  the  subnnaxillary  lymph  glands ;  the  external  maxillary 
artery  turns  round  between  it  and  the  lower  border  of  the 
mandible  at  the  anterior  border  of  the  masseter  ;  and  the  sub- 
mental branch  of  the  external  maxillary  artery  runs  anteriorly 
in  the  angle  between  it  and  the  bone. 

The  lateral  surface  is  in  relation  posteriorly  with  the  lower 


Parotid  duct 

Accessory  parotid  gland 

Internal  pterygoid 


Lingual  nerve 
Mandible 

Mylo-hyoid 

n  III  1i1  ^^^'^^^^^^^W^^^B^^^^^^!'!!!^^Ki'^'''^^s^^^^^^^KI^MW'''~~~  ~~~^ Surface  of  submaxil- 
01  J      V^^l^^^^^^^KK!^  ^I^HII^HHf'^SiHHHV  *  ~         lary  gland  covered 

Submaxillary  duel/      /       /      /        /  ^fc ,  y  \' JlMIIHWfe. 'IMP^  by  mandible 

Mucous  membrane/     /      /       /      /li|M4\ 

Sublingual  glahd/      /       /      /     imlill«i\%\lWM^-      ilMMl  integument  and  fascia 

Tongue* 
Mylo-hyoid 
Anterior  belly  of  digastric' 

Fig.  114. — Dissection  of  the  Parotid,  Submaxillary,  and  Sublingual  Glands. 

part  of  the  medial  surface  of  the  internal  pterygoid,  and 
anteriorly  with  the  inner  surface  of  the  body  of  the  mandible 
below  the  mylo-hyoid  ridge.  The  external  maxillary  artery, 
after  it  emerges  from  the  groove  in  the  posterior  end  of  the 
gland,  and  before  it  turns  round  the  lower  border  of  the 
mandible,  runs  anteriorly  and  downwards  between  this  surface 
and  the  internal  pterygoid  ;  and  the  mylo-hyoid  artery  and 
nerve  lie  between  it  and  the  body  of  the  mandible  before 
they  pass,  more  anteriorly,  to  the  medial  surface  of  the  gland. 


284  HEAD  AND  NECK 

The  medial  surface  is  in  relation  with  the  mylo-hyoid  and 
hyoglossus,  the  lingual  nerve  and  the  submaxillary  ganglion, 
and  the  hypoglossal  nerve.  It  overlaps  the  stylo-hyoid 
muscle,  both  bellies  of  the  digastric,  and  the  great  cornu  of 
the  hyoid  bone ;  and  the  deep  part  of  the  gland  and  the  duct 
both  spring  from  this  surface  before  they  pass  anteriorly 
between  the  mylo-hyoid  and  the  hyoglossus  muscles. 

The  nerve  supply  of  the  gland  is  derived  from  the  lingual 
nerve,  the  submaxillary  ganglion,  the  sympathetic  plexus  on 
the  external  maxillary  artery ;  and  its  vascular  supply  consists 
of  small  submaxillary  branches  from  the  external  maxillary 
artery. 

The  relations  of  the  deep  part  of  the  gland  and  the  duct 
will  be  investigated  after  the  mylo-hyoid  has  been  reflected. 

Dissection. — Displace  the  superficial  part  of  the  gland  and  the  submental 
branch  of  the  external  maxillary  artery  posteriorly  ;  cut  the  mylo-hyoid 
vessels  and  nerve,  and  turn  the  anterior  belly  of  the  digastric  downwards ; 
then  clean  the  mylo-hyoid  muscle  and  examine  its  attachments. 

Musculus  Mylohyoideus.  —  This  is  a  thin  sheet  of 
muscular  fibres,  which  arises  from  the  mylo-hyoid  ridge 
upon  the  inner  surface  of  the  body  of  the  mandible,  by 
an  origin  which  extends  from  the  last  molar  tooth  to  the 
symphysis.  Its  fibres  are  directed  downwards,  medially, 
and  anteriorly,  and  present  two  different  modes  of  insertion. 
The  posterior  fibres  are  inserted  into  the  body  of  the  hyoid 
bone ;  these,  however,  form  a  comparatively  small  part  of 
the  muscle.  The  greater  number  of  the  fibres  are  inserted 
into  a  median  raphe,  which  extends  between  the  symphysis 
of  the  lower  jaw  and  the  body  of  the  hyoid  bOne.  The 
two  mylo-hyoid  muscles,  therefore,  stretch  across  from  one 
side  of  the  body  of  the  mandible  to  the  other,  in  front  of  the 
hyoid  bone,  and  constitute  a  floor  for  the  anterior  part  of  the 
mouth.  This  floor  is  frequently  termed  the  diaphragma  oris. 
The  mylo-hyoid  muscle  is  supplied  by  the  mylo-hyoid  branch 
of  the  inferior  alveolar  nerve. 

Dissection. — Cut  the  mylo-hyoid  muscle  a  little  below  its  origin  from  the 
mylo-hyoid  ridge  and  turn  it  downwards  and  anteriorly.  Whilst  doing 
this  be  careful  not  to  injure  the  mvicous  membrane  of  the  mouth  which 
lies  in  contact  with  it  above. 

Parts  exposed  by  the  Reflection  of  the  Mylo-hyoid  (Fig. 
115). — The  side  of  the  tongue  is  now  brought  into  view, 
with  a   number   of  structures  in  connection   with   it.      First 


SUBMAXILLARY  REGION 


285 


note  the  mucous  membrane  stretching  from  the  tongue  to 
the  gum  of  the  lower  jaw ;  then  identify  the  various  muscles. 
The  hyoglossus,  a  portion  of  which  was  previously  visible 
behind  the  mylo-hyoid,  is  fully  exposed.  It  is  a  quadrangular 
sheet  of  fleshy  fibres  which  extends  from  the  hyoid  bone  to 
the  side  of  the  tongue.  Mark  its  position,  because  all  the 
structures  in  this  region  have  a  more  or  less  intimate  relation- 
ship to  it.  Thus,  posterior  and  also  superficial  to  its  upper 
part,  the  stylo-glossus  muscle  will  be  recognised,  whilst  anterior 


glossus 

lo-pharyngeus 
Glosso-pliaryngeal 
ner\e 

Stylo-hyoid 
igament 

Lingual  nerve 


Deep  part  of  submaxillary  gland 
Submaxillary  ganglion 

Submaxillary  duct  (Wharton's) 

Cut  edge  of  mucous  membrane 
Sublingual  gland 

Sublingual  artery 

Genio- 
glossus 


Lingual  artery 
Middle  constrictor 


Lingual  artery 


enio-hyoid 


Hypoglossal  nerve 
Supra-hyoid  artery 

Fig.  115. — Dissection  of  Submaxillary  Region. 

to  it  are  the  gento-glossus  and  the  genio-hyoid.  The  genio- 
hyoid muscle  occupies  the  antero-inferior  part  of  the  region, 
whilst  the  anterior  part  of  the  genio-glossus  is  seen  in  the 
interval  between  it  and  the  hyoglossus.  Upon  the  surface  of 
the  hyoglossus,  the  lingual  and  hypoglossal  nerves,  the  con- 
necting loop  between  them,  the  deep  portion  of  the  sub- 
maxillary gland  with  the  submaxillary  duct,  and  the  submaxillary 
ganglion  are  to  be  dissected.  The  lingual  nerve  occupies  the 
highest  level,  and  passes  anteriorly  upon  the  muscle  near  its 
insertion  into  the  tongue.  The  hypoglossal  nerve,  with  its 
ve7ia  comitans,  crosses  it  close  to  the  hyoid  bone,  whilst  the 


286 


HEAD  AND  NECK 


deep  part  of  the  submaxillary  gland  and  the  submaxillary  duct 
(Wharton's)  occupy  an  intermediate  place.  Although  the 
submaxillary  ganglion  is  very  minute,  its  relations  are  so 
precise  that  it  is  very  easily  found.  By  seizing  the  lingual 
nerve  and  dissecting  carefully  in  the  interval  between  it 
and  the  deep  part  of  the  submaxillary  gland,  the  ganglion 
will  be  exposed,  and  its  roots  and  branches  of  distribution 
made    out.         Upon    the    genio  -  glossus,    anterior    to    the 


Internal  pterygoid^ 
External  pterygoid 


Inferior  nasal  concha  (O.T.  inferior  turbinal) 
Soft  palate 


Temporal  muscle 


Stylo-glossus 

Inferior  alveolar 

vessels  and  nerve 

Lingual  nerve 

External 
maxillary  artery 
Superficial  part  of    ^  „ 
submaxillary  gland     V; 
Submaxillary  duct^<' 
Deep  part  of 
submaxillary  gland 
Hypoglossal  nerve 

Lingual  artery 

Hyoglossus 
Mylo-hyo 
Digastric  tendon 

Genio-hyoid 


Tongue 


Inferior  alveolar 
vessels  and  nerve 
in  the  mandib- 
ular canal 
External 
maxillary  artery 


/^7\Mylo-hyoid 
/, '^Lingual  nerve 
■\Deep  part  of 
.^Ky^y\    submaxillary  gland 
V>\,^    Submaxillary  duct 
^^        Hypoglossal  nerve 

_  Lmgual  artery 
Digastric 
Hyoglossus 


Genio-hyoid 


Fig. 


-Frontal  section  through  the  Tongue  and  Submaxillary  Region 
in  a  plane  posterior  to  the  molar  teeth. 


hyoglossus,  the  dissector  will  note  the  sublingual  gland  with 
its  artery  of  supply.  If  the  stylo-hyoid  and  the  posterior 
belly  of  the  digastric  are  displaced  posteriorly,  certain 
structures  will  be  seen  passing  under  cover  of  the  posterior 
margin  of  the  hyoglossus  muscle.  These  are: — (i)  the 
glosso-pharyngeal  nerve  immediately  below  the  stylo-glossus 
muscle;  (2)  the  stylo-hyoid  ligament  a  little  lower  down; 
and  (3)  the  lingual  artery  close  to  the  hyoid  bone. 

Musculus  Hyoglossus. — This  is  a  quadrate,  flat  muscle  which 
arises  from  the  whole  length  of  the  greater  cornu,  and  also  from 


SUBMAXILLARY  REGION 


2^7 


the  body  of  the  hyoid  bone.  Its  fibres  pass  upwards  to  the 
posterior  part  of  the  side  of  the  tongue,  medial  to  the  stylo- 
glossus. The  hyoglossus  is  supplied  by  the  hypoglossal 
nerve. 

Musculus  Stylo-glossus. — The  stylo-glossus   muscle  is  an 
elongated  fleshy  slip  which  takes  origin  from  the  anterior  aspect 
of  the  styloid  process  near  its  tip,  and,  to  a  slight  extent,  from 
the  upper  part  of  the  stylo-hyoid  ligament  also.     Passing  down- 
inferior  meatus  of  nose 
Maxillary  sinus 


Tongue. 


Great  posterior 
palatine  artery 
and  nerve 
Vestibule  of 
mouth 


Buccinator 


Arteria  profunda 
linguae 


/, Sublingual  gland 

Inferior  alveolar 
artery  and  ner\'e 
in  the  mandibular 
canal 


Mylo-hyoid 


Genio-glossus 


Genio-hyoid 


Platysma 


Anterior  bellj'  of  digastric 


Fig.   117. — Frontal  section  through  the  Closed  Mouth  in  the  plane 
of  the  second  molar  teeth. 

wards  and  anteriorly  its  fibres  may  be  traced  upon  the  side 
of  the  tongue  as  far  as  the  tip.  Some  of  them  decussate 
with  the  fasciculi  of  the  hyoglossus  muscle.  The  nerve  of 
supply  to  the  stylo-glossus  comes  from  the  hypoglossal. 

Musculus  Geniohyoideus.  —  The  genio-hyoid  muscle  is 
placed  close  to  the  median  plane,  in  contact  with  its  fellow  of 
the  opposite  side.  It  is  a  short  muscle  which  arises  from 
the  spina  mentalis  upon  the  posterior  surface  of  the  symphysis 
of  the  mandible,  and  extends  downwards  and  posteriorly  to 
gain  insertion  into  the  anterior  aspect  of  the  body  of  the 
hyoid  bone.     The  hypoglossal  nerve  supplies  the  genio-hyoid. 


288  HEAD  AND  NECK 

The  Deep  Part  of  the  Submaxillary  Gland. — It  has  been 
noted  already  that  the  small  deep  part  of  the  submaxillary 
gland  springs  from  the  medial  surface  of  the  superficial  part  at 
the  posterior  border  of  the  mylo-hyoid  muscle.  It  will  now  be 
obvious  that  it  passes  anteriorly  and  upwards,  between  the 
mylo-hyoid  laterally  and  the  hyo-glossus  and  genio-glossus 
medially,  until  it  comes  into  contact  with  the  sublingual  gland. 
It  is  accompanied  by  the  lingual  nerve  and  the  submaxillary 
duct,  both  of  which  lie  on  its  medial  surface. 

Ductus  Submaxillaris. — The  duct  of  the  submaxillary 
gland  (O.T.  Wharton's  duct)  emerges  from  the  medial  surface 
of  the  main  part  of  the  gland,  and  proceeds,  with  the  deep 
part  of  the  gland,  anteriorly  and  upwards  upon  the  hyo- 
glossus  muscle.  At  first  it  lies  between  the  lingual  nerve 
above  and  the  hypoglossal  nerve  below.  Reaching  the 
surface  of  the  genio-glossus  muscle,  it  is  crossed  laterally, 
and  then  below  and  medially,  by  the  lingual  nerve.  Then  it 
passes  to  the  medial  side  of  the  sublingual  gland,  and  gains  the 
floor  of  the  mouth,  where  it  opens  by  a  small  orifice  placed 
on  the  summit  of  a  papilla  which  lies  close  to  the  side  of  the 
frenulum  linguae. 

The  wall  of  the  duct  is  much  thinner  than  that  of 
the  parotid  duct.  If  a  small  opening  be  made  in  it,  the 
dissector  will  experience  little  difficulty  in  passing  a  fine  probe 
or  bristle  along  it  into  the  mouth. 

G-landula  Sublingualis. — The  sublingual  gland  lies  in  the 
floor  of  the  mouth,  and  is  the  smallest  of  the  larger  salivary 
glands.  It  is  almond  shaped,  about  one  inch  and  a  half 
long  ;  and  its  relations  are  very  definite.  Its  prominent  upper 
border  can  be  seen  within  the  mouth,  beneath  the  anterior 
part  of  the  tongue,  where  it  is  covered  by  a  fold  of  mucous 
membrane  termed  the  plica  sublingualis  (Fig.  146).  Medially 
it  rests  upon  the  genio-glossus  muscle,  whilst  laterally  it  is 
lodged  in  a  fossa  on  the  inner  aspect  of  the  mandible, 
immediately  lateral  to  the  symphysis  and  above  the  mylo- 
hyoid ridge.  Below,  it  is  supported  by  the  mylo  -  hyoid 
muscle.  Its  anterior  extremity  reaches  the  median  plane, 
above  the  anterior  border  of  the  genio  -  glossus,  and  is  in 
contact  with  its  fellow  of  the  opposite  side.  The  duct  of 
the  submaxillary  gland  and  the  lingual  nerve  are  prolonged 
anteriorly  medial  to  the  sublingual  gland. 

Numerous  small  ducts  (the   number   varying  from   eight 


SUBMAXILLARY  REGION  289 

to  twenty)  proceed  from  the  sublingual  gland.  These,  as  a 
rule,  open  into  the  mouth  on  the  summit  of  the  plica  sub- 
lingualis (Birmingham). 

NervTis  Lingualis. — In  the  dissection  of  the  infratemporal 
region,  the  lingual  nerve  was  seen  passing  downwards  between 
the  ramus  of  the  mandible  and  the  internal  pterygoid  muscle. 
As  it  descends  it  inclines  anteriorly,  and,  after  passing 
over  the  attachment  of  the  superior  constrictor  muscle  of 
the  pharynx  to  the  posterior  end  of  the  mylo-hyoid  ridge, 
it  lies  below  and  posterior  to  the  last  molar  tooth  between  the 
mucous  membrane  of  the  mouth  and  the  body  of  the  mandible. 
At  this  point  it  is  in  danger  of  being  hurt  by  the  clumsy 
extraction  of  one  of  the  lower  molars,  and  here  also  it  may 
be  divided  by  the  surgeon,  from  the  inside  of  the  mouth. 
In  its  further  course  the  nerve  keeps  close  to  the  side  of 
the  tongue,  crossing  the  styloglossus  and  the  upper  part  of 
the  hyoglossus,  and,  beyond  that,  the  submaxillary  duct. 
Its  terminal  branches  are  placed  immediately  under  the 
mucous  membrane  of  the  mouth,  and  it  can  be  traced  as 
far  as  the  tip  of  the  tongue. 

The  branches  which  proceed  from  the  lingual  nerve  in  the 
submaxillary  region  are  of  two  kinds — (i)  twigs  of  com- 
munication ;  (2)  branches  of  distribution. 


r  I.   Two  or  more  to  the  submaxillary  ganglion. 
I   2.    ' 


Twigs  of         I   2.   One    or   two    which   descend   along   the   anterior 
border  of  the  hyoglos 
the  hypoglossal  nerve. 


Communication."!  border  of  the  hyoglossus  muscle  to  unite  with 


■D         1  r  I.   Slender  filaments  to  the  mucous  membrane  of  the 

israncnes  ,,        j 

c  I  mouth  and  gums. 

Distribution.  1   ^-   A  few  twigs  to  the  sublingual  gland. 
V  3.   -Branches  to  the  tongue. 

The  lingual  branches  pierce  the  substance  of  the  tongue, 
and  then  incline  upwards  to  supply  the  mucous  membrane 
with  the  papillae  over  the  anterior  two-thirds  of  this  organ. 

Ganglion  Submaxillare. — This  is  a  minute  ganglion  which 
lies  upon  the  upper  part  of  the  hyoglossus  muscle  in  the  interval 
between  the  lingual  nerve  and  the  deep  part  of  the  sub- 
maxillary gland.  In  size,  it  is  not  larger  than  the  head  of  a 
large  pin;  and,  when  freed  from  the  connective  tissue  surround- 
ing both  it  and  its  branches,  it  will  be  seen  to  be  suspended 
from  the  lingual  nerve  by  two  short  branches,  which  enter  its 
upper  border,  and  are  separated  by  a  distinct  interval.  Of  these, 
the  posterior  connecting  twig  is  frequently  in  the  form  of  two 

VOL.  II — 19 


290  HEAD  AND  NECK 

or  three  filaments,  which  convey  to  the  gangUon  its  sensory 
and  secretory  roots,  whilst  the  anterior  connecting  branch  must 
be  looked  upon  as  a  twig  given  by  the  ganglion  to  the  lingual 
nerve. 

In  common  with  the  other  ganglia  developed  in  connection 
with  the  branches  of  the  trigeminal  nerve,  this  ganglion  has 
three  roots — viz.  (i)  a  sensory  root  from  the  lingual  nerve  ;  (2) 
a  secretory  root  from  the  chorda  tympani ;  and  (3)  a  sympathetic 
root  from  the  plexus  around  the  external  maxillary  artery. 

From  its  lower  border  several  minute  twigs  proceed,  and 
these  are  distributed  —  (i)  to  the  submaxillary  gland  and 
duct ;  (2)  to  the  sublingual  gland  from  the  branch  which 
it  gives  to  the  lingual  nerve ;  and  (3)  to  the  mucous  mem- 
brane of  the  mouth. 

Nervus  Hypoglossus. — This  nerve  has  been  traced  in  the 
dissection  of  the  anterior  triangle  to  the  point  where  it 
disappears  under  cover  of  the  mylo-hyoid  muscle  (p.  231). 
It  is  now  seen  passing  anteriorly  upon  the  hyoglossus  muscle, 
above  the  hyoid  bone  and  below  the  level  of  the  deep 
part  of  the  submaxillary  gland.  At  the  anterior  border  of 
the  hyoglossus  it  gains  the  surface  of  the  genio  -  glossus 
muscle,  into  the  substance  of  which  it  sinks ;  and  finally 
it  breaks  up  into  branches  which  supply  the  muscular  sub- 
stance of  the  tongue.  Upon  the  hyoglossus  muscle  it  is 
accompanied  by  a  vena  comitans. 

The  branches  which  spring  from  the  hypoglossal  nerve  in 
this  region  are  very  numerous,  and  are  entirely  distributed  to 
muscles.  It  supplies — (i)  thestylo-glossus;  (2)  the  hyoglossus; 
(3)  the  genio-glossus ;  (4)  the  genio-hyoid ;  and  (5)  the 
intrinsic  muscles  of  the  tongue. 

In  addition,  it  communicates  freely  with  the  lingual 
nerve.  The  more  apparent  of  these  connections  take  place 
in  the  form  of  one  or  more  loops  in  relation  to  the  anterior 
border  of  the  hyoglossus.  Other  communications  with  the 
same  nerve  are  effected  in  the  substance  of  the  tongue. 

Reflection  of  the  Hyoglossus. — The  hyoglossus  should  now  be 
carefully  detached  from  the  hyoid  bone,  and  thrown  upwards  towards 
the  tongue.  In  doing  this  there  is  no  need  to  divide  the  structures 
which  lie  upon  its  surface.  By  the  reflection  of  this  muscle  the  follow- 
ing structures  will  be  fully  displayed — (i)  the  profunda  linguae  artery 
and  the  veins  which  accompany  it ;  (2)  the  dorsales  linguae  arteries  and 
veins  ;  (3)  the  posterior  part  of  the  genio-glossus  ;  (4)  the  origin  of  the 
middle  constrictor  of  the  pharynx  ;  and  (5)  the  attachment  of  the  stylo- 
hyoid ligament. 


SUBMAXILLARY  REGION  291 

Musculus  Genioglossus. — This  is  a  flat  triangular  muscle, 
the  medial  surface  of  which  is  in  contact  with  its  fellow  of 
the  opposite  side  in  the  median  plane.  It  arises  by  a  short 
pointed  tendon  from  the  upper  mental  spine  on  the  posterior 
aspect  of  the  symphysis  of  the  mandible,  and  from  this  its 
fleshy  fasciculi  spread  out  in  a  fan-shaped  manner.  By  far 
the  greater  part  of  the  muscle  is  inserted  into  the  tongue  by 
an  insertion  which  extends  throughout  the  whole  length  of 
the  organ  from  the  tip  to  the  base ;  below  the  tongue,  a 
few  fibres  reach  the  side  of  the  pharynx.  The  genio-glossus 
is  supplied  by  twigs  from  the  hypoglossal  nerve. 

Arteria  Lingualis.  —  As  the  lingual  artery  is  now  fully 
exposed,  it  can  be  conveniently  studied  at  this  stage. 
It  springs  from  the  anterior  aspect  of  the  external  carotid, 
and  is  separable  into  two  parts — viz.  (i)  a  part  extending 
from  its  origin  to  the  posterior  border  of  the  hyoglossus 
muscle;  (2)  a  part  lying  in  relation  to  the  upper  border  of 
the  hyoid  bone  and  extending  to  the  anterior  border  of  the 
hyoglossus,  where  it  divides  into  two  terminal  branches,  the 
sublingual  and  the  deep  artery  of  the  tongue. 

The  first  part  has  been  fully  examined  in  a  previous 
dissection.  It  lies  in  the  carotid  triangle  of  the  neck,  and 
is  therefore  comparatively  superficial.  It  is  crossed  by  the 
hypoglossal  nerve,  and  lies,  medially,  against  the  middle 
constrictor.  The  second  part  proceeds  anteriorly  along  the 
upper  border  of  the  great  cornu  of  the  hyoid  bone,  and 
is  covered  by  the  hyoglossus  muscle,  which  intervenes 
between  it  and  the  hypoglossal  nerve.  The  nerve,  how- 
ever, is  placed  at  a  slightly  higher  level.  The  deep  or 
medial  relations  of  the  artery  in  this  stage  of  its  course 
are  the  middle  constrictor  of  the  pharynx  and  the  genio- 
glossus. 

The  branches  of  the  lingual  artery  are  : — 

1.  Suprahyoid  from  'CtvQ  first  part  (p.  233). 

2.  Dorsalis  lingua  from  the  second  part. 

3.  Sublingual. 

4.  Profunda. 

Ra7ni  Dorsales  Linguce. — The  dorsalis  linguae  is  generally 
represented  by  two  or  more  well-marked  branches,  which 
pass  upwards,  under  cover  of  the  hyoglossus  muscle,  to  end 
in  twigs  to  the  mucous  membrane  covering  the  pharyngeal 
part  of  the  dorsum  of  the  tongue.  Some  twigs  are  supplied 
II— 19  a 


292  HEAD  AND  NECK 

also  to  the  muscular  substance  of  the  organ,  and  a  few  may 
be  traced  backwards  into  the  tonsil. 

Arteria  Sublingualis. — This  springs  from  the  termination 
of  the  second  part  and  emerges  from  under  cover  of  the 
anterior  border  of  the  hyoglossus,  and  then  ascends  upon  the 
genio-glossus  to  reach  the  sublingual  gland,  which  it  supplies. 
It  gives  branches  to  the  surrounding  muscles  also ;  and 
it  anastomoses  with  its  fellow  of  the  opposite  side  and  with 
the  submental  branch  of  the  external  maxillary  artery. 

Arteria  Profunda  Linguce. — The  deep  artery  of  the  tongue 
ascends  almost  vertically  upon  the  genio-glossus,  overlapped 
by  the  anterior  border  of  the  hyoglossus  ;  when  it  reaches 
the  under  surface  of  the  tongue,  it  runs  towards  the  tip  and 
ends  in  terminal  branches.  It  can  easily  be  exposed  by 
dividing  the  mucous  membrane  along  its  course,  when  it  will 
be  seen  to  lie  close  to  the  attachment  of  the  frenulum  of 
the  tongue,  and  to  be  continued  forwards  in  the  interval 
between  the  genio-glossus  and  the  inferior  longitudinal 
muscle.  Its  course  is  tortuous  to  allow  of  the  protrusion  or 
elongation  of  the  organ,  and  it  gives  off  numerous  branches. 

Lingual  Veins. — The  lingual  artery  is  accompanied  by 
two  small  venae  comites  which  lie  with  it  under  cover  of 
the  hyoglossus ;  but  the  main  vein  of  the  tongue  crosses 
the  lateral  surface  of  the  hyoglossus,  and  another  smaller  vein, 
the  vena  comitans  hypoglossi,  accompanies  the  hypoglossal 
nerve.  The  venae  comites  of  the  artery  and  the  vena  comitans 
hypoglossi  unite  with  the  main  vein  to  form  the  lingual  vein, 
which  opens  into  the  common  facial  vein  or  into  the  internal 
jugular  vein. 

Stylo-hyoid  Ligament. — This  is  the  last  structure  to  be 
examined  in  this  dissection.  It  is  a  fibrous  cord  which 
springs  from  the  tip  of  the  styloid  process  and  passes 
antero-inferiorly  to  be  attached,  under  cover  of  the  hyo- 
glossus muscle,  to  the  lesser  cornu  of  the  hyoid  bone.  It  is 
not  uncommon  to  find  it  partially  ossified ;  in  other  cases 
it  may  assume  a  ruddy  hue  and  contain  muscular  fibres. 

OTIC    GANGLION    AND    TENSOR   PALATL 

During  the  dissection  of  the  submaxillary  region  the 
dissector  has  noted  a  nerve  ganglion,  the  submaxillary  ganglion^ 
connected  with  the  lingual  branch  of  the  mandibular  nerve. 


OTIC  GANGLION  AND  TENSOR  PALATI     293 

and  when  he  was  examining  the  infratemporal  region  refer- 
ence was  made  to  the  otic  gangHon,  which  is  associated 
with  the  trunk  of  the  mandibular  nerve  and  the  branch  which 
it  supplies  to  the  internal  pterygoid  muscle.  This  ganglion 
and  its  connections  should  now  be  displayed,  and  afterwards 
the  tensor  palati  muscle  should  be  cleaned  and  followed  from 
its  origin  to  the  hamulus  of  the  medial  pterygoid  lamina. 

Dissection. — Cut  the  lingual  and  inferior  alveolar  nerves  immediately 
below  their  origins  ;  evert  the  upper  part  of  the  mandibular  nerve  and 
examine  the  otic  ganglion  ;  then  divide  the  internal  pterygoid,  along  the 
posterior  border  of  the  lateral  pterygoid  lamina,  depress  the  lower  part  of 
the  muscle  and  clean  the  tensor  palati,  which  forms  the  medial  relation 
of  the  middle  meningeal  artery,  the  otic  ganglion  and  the  mandibular  nerve, 
separating  them  from  the  lateral  surface  of  the  auditory  tube  (Eustachian). 

Ganglion  Oticum. — This  is  a  minute  oval  body  about 
4  mm.  in  length.  It  lies  immediately  below  the  foramen 
ovale,  between  the  mandibular  nerve  laterally,  the  tensor  veli 
palatini  medially,  and  the  middle  meningeal  artery  posteriorly ; 
and  it  is  intimately  associated  with  the  origin  of  the  nerve  to 
the  internal  pterygoid. 

The  otic  ganglion  is  usually  described  as  receiving  motor,  sensory,  and 
sympathetic  roots.  The  7notor  root  is  suppUed  by  the  nerve  to  the  internal 
pterygoid  muscle  ;  the  sympathetic  root  comes  from  the  plexus  around  the 
middle  meningeal  artery.  In  addition  to  these,  the  small  superficial  petrosal 
nerve  enters  the  posterior  border  of  the  ganglion,  and  conveys  to  it  sensory 
fibres. 

The  following  are  the  branches  which  proceed  from  the  otic  ganglion  : — 

f  A  tv»dg  which  passes  downwards  and  anteriorly  to  the 
Branches  of     |        tensor  veli  palatini.     (Tensor  palati.) 
distribution,    "j  A   twig   which    proceeds   upwards    and    posteriorly    to 

y       supply  the  tensor  tympani. 

{One  or  more  fine  filaments  to  one  or  both  of  the  roots 
of  the  auriculo-temporal  nerve. 
A    minute    communicating    filament     to    the    chorda 
tympani. 

Musculus  Tensor  Veli  Palatini. — This  flat  and  band-like 
muscle  is  closely  applied  to  the  deep  surface  of  the  internal 
pterygoid  muscle.  It  arises  from  the  scaphoid  fossa  at  the 
root  of  the  medial  pterygoid  lamina,  from  the  posterior 
border  of  the  lower  surface  of  the  great  wing  of  the  sphenoid, 
from  the  spine  of  the  sphenoid,  and  from  the  lateral  aspect  of 
the  auditory  tube  (O.T.  Eustachian).  It  descends  to  the 
lower  end  of  the  medial  pterygoid  lamina  and  ends  in  a 
tendon  which  turns  horizontally  under  the  hamulus  into 
the  soft  palate,  where  its  attachments  will  be  seen  later. 

11—19  h 


294  HEAD  AND  NECK 


THE    GREAT    VESSELS    AND    NERVES 
OF    THE    NECK. 

As  soon  as  the  dissection  of  the  infratemporal  and  the 
submaxillary  regions  is  completed  the  dissector  should  turn 
to  the  study  of  the  external  carotid  artery  and  its  relations. 

Arteria  Carotis  Externa. — The  external  carotid  is  one 
of  the  two  terminal  branches  of  the  common  carotid.  It 
commences  therefore  at  the  level  of  the  upper  border  of  the 
thyreoid  cartilage,  opposite  the  disc  between  the  third  and 
fourth  cervical  vertebrae ;  and,  after  running  upwards  and 
posteriorly  to  the  level  of  the  neck  of  the  mandible,  it 
terminates,  between  that  portion  of  bone  and  the  upper  part 
of  the  antero-medial  surface  of  the  parotid  gland,  by  dividing 
into  two  terminal  branches,  the  superficial  temporal  and  the 
internal  maxillary.  At  its  commencement  it  lies  anterior  and 
medial  to  the  internal  carotid ;  and  it  is  called  external  not 
on  account  of  its  relation  to  the  internal  carotid,  but  because 
it  is  distributed  mainly  to  the  parts  on  the  exterior  of  the 
skull.  It  is  at  first  comparatively  superficial  in  the  upper 
part  of  the  carotid  triangle ;  next  it  passes  under  cover  of  the 
lower  part  of  the  postero-medial  surface  of  the  parotid  and  the 
posterior  belly  of  the  digastric  and  the  stylo-hyoid  muscles. 
At  the  upper  border  of  the  stylo-hyoid  it  enters  a  groove  in 
the  medial  border  of  the  parotid,  through  which  it  passes  to 
the  upper  part  of  the  antero-medial  surface  of  the  gland, 
posterior  to  the  neck  of  the  mandible,  where  it  terminates. 

Relations. — As  it  lies  in  the  carotid  triangle  it  is  covered 
by  the  skin,  superficial  fascia  and  platysma,  branches  of  the 
nervus  cutaneus  colli  and  the  cervical  branch  of  the  facial 
nerve,  and  the  deep  fascia.  Beneath  the  deep  fascia  it  is 
crossed  superficially  by  the  common  facial  and  lingual  veins 
and  the  hypoglossal  nerve ;  and,  at  the  upper  end  of  the 
triangle,  it  is  concealed  by  the  lower  end  of  the  parotid  gland 
and  it  is  crossed  from  behind  forwards  by  the  posterior  facial 
vein.  After  it  leaves  the  carotid  triangle  it  is  overlapped  by 
the  angle  of  the  mandible,  and  is  crossed  by  the  posterior 
belly  of  the  digastric  and  the  stylo-hyoid.  At  its  termina- 
tion it  is  concealed  by  the  upper  part  of  the  parotid  and  is 
crossed  by  branches  of  the  facial  nerve. 


GREAT  VESSELS  AND   NERVES  OF  NECK     295 


To  its  medial  side  lies  the  wall  of  the  pharynx,  from  which 
it  is  separated,  in  the  region  of  the  carotid  triangle,  by  the 
external    and    internal    laryngeal    branches    of   the    superior 


Accessory 


-Vagus 

-Jugular  ganglion 


Ganglion 
nodosum 

Pharyngeal 
branch 


Superior  laryngeal 


Hypoglossal 


Descendens  hypcfglossi 

Ascending  pharyngeal 
Internal  carotid 


Glosso-pharyngeal 
Superficial  temporal 

Internal  maxillary 


External 
carotid 


Posterior 
auricular 

^Occipital 


External 
maxillary 

Lingual 

Branch  to 
thyreo-hj'oid 
Internal 
laryngeal 


External 
lar^'ngeal 


Common  carotid 


Fig    118  —Diagram  of  Carotid  System  of  Vessels  in  the  Neck  with  the 
Glosso-pharyngeal,  Vagus,  Accessory,  and  Hypoglossal  Nerves. 

laryngeal  nerve.  The  medial  relations  at  a  higher  level  will 
be  seen  to  greater  advantage  at  a  later  stage  when  the  styloid 
process  is  detached  and  displaced.  They  are  the  pharyngeal 
branch  of  the  vagus,  the  stylo-pharyngeus,  the  glosso-pharyngeal 
11—19  c 


296  HEAD  AND  NECK 

nerve,  and  the  styloid  process  or  the  stylo-hyoid  Hgament. 
These  structures  he  to  its  medial  side  after  they  have  passed 
obhquely  between  it  and  the  internal  carotid,  which  has 
gradually  attained  a  plane  posterior  and  medial  to  that  in 
which  the  external  carotid  Hes. 

In  the  whole  of  its  extent  the  external  carotid  is  accom- 
panied by  numerous  sympathetic  nerve  fibres,  derived  from 
the  upper  cervical  sympathetic  gangfion  ;  they  constitute  the 
external  carotid  plexus^  which  distributes  offsets  along  all  the 
branches  of  the  artery. 

Branches. — The  branches  of  the  external  carotid  artery  are 
the  superior  thyreoid,  the  lingual,  and  the  external  maxillary 
from  its  anterior  aspect ;  the  occipital  and  the  posterior 
auricular  from  its  posterior  aspect ;  the  ascending  pharyngeal 
from  its  medial  side ;  and  the  superficial  temporal  and  the 
internal  maxillary  are  its  terminal  branches. 

Arteria  Thyreoidea  Superior. — This  vessel  arises  within 
the  carotid  triangle,  from  the  anterior  aspect  of  the  external 
carotid  close  to  its  origin.  It  runs  downwards  and  anteriorly, 
under  cover  of  the  omo-hyoid,  sterno-hyoid,  and  sterno-thyreoid 
muscles,  to  the  apex  of  the  lateral  lobe  of  the  thyreoid  gland, 
where  it  ends  by  breaking  up  into  three  terminal  branches. 

The  following  branches  proceed  from  it : — 


1.  Hyoid. 

2.  Superior  laryngeal. 

3.  Sterno-mastoid. 


4.  Crico-thyreoid. 

5.  Glandular. 


Ramus  Hyoideus. — This  is  a  minute  twig,  which  springs 
from  the  superior  thyreoid  in  the  carotid  triangle.  It  runs 
along  the  lower  border  of  the  hyoid  bone,  under  cover  of  the 
thyreo-hyoid  muscle,  and  anastomoses  with  its  fellow  of  the 
opposite  side,  and  with  the  hyoid  branch  of  the  lingual 
artery. 

Arteria  Laryngea  Superior. — This  is  a  larger  vessel.  It 
springs  from  the  superior  thyreoid  in  the  carotid  triangle, 
and,  associating  itself  with  the  internal  laryngeal  nerve,  it 
enters  the  pharynx  after  piercing  the  thyreo-hyoid  mem- 
brane. 

Arteria  Sternocleidomastoidea. — The  sterno-mastoid  branch 
is  a  small  vessel  which  runs  downwards  and  posteriorly,  across 
the  carotid  sheath  along  the  upper  border  of  the  anterior 
belly  of  the  omxO-hyoid  muscle,  to  reach  the  deep  surface  of 
the    sterno-mastoid   muscle,  into  which  it  sinks.      It    gives. 


GREAT  VESSELS  AND  NERVES  OF  NECK     297 

in  addition,  minute  twigs  to  the  depressor  muscles  of  the 
larynx. 

Ramus  Cricothyreoideiis. — The  crico- thyreoid  artery  runs 
medially  upon  the  crico-thyreoid  ligament,  and  anastomoses 
with  its  fellow  of  the  opposite  side.  It  has  already  been 
noticed  in  the  dissection  of  the  middle  line  of  the  neck 
(p.  229). 

Rmni  Glandulares. — The  glandular  rami  are  the  three 
terminal  branches.  They  spring  from  the  main  trunk  at 
the  apex  of  the  lateral  lobe  of  the  thyreoid  gland.  The 
largest  is  distributed  on  the  medial  surface  of  the  lateral 
lobe ;  the  smallest  ramifies  on  its  lateral  surface ;  whilst 
the  third  runs  downwards  upon  the  anterior  border  of  the 
lateral  lobe,  and  then  along  the  upper  border  of  the  isthmus 
towards  its  fellow  of  the  opposite  side.  The  anastomosis 
between  the  thyreoid  arteries  of  the  two  sides  is  by  no  means 
free. 

Vena  Thyreoidece  Superiores. — The  superior  thyreoid  veins 
emerge  from  the  gland  and  form  a  trunk  which  receives 
tributaries  corresponding  in  a  great  measure  with  the  branches 
of  the  artery.  It  crosses  the  upper  part  of  the  common 
carotid  and  joins  the  internal  jugular  vein. 

Arteria  Lingualis. — The  lingual  artery  springs  from  the 
external  carotid  at  the  level  of  the  great  cornu  of  the 
hyoid  bone  in  the  carotid  triangle.  It  runs  along  the  upper 
border  of  the  great  cornu.  As  its  name  indicates  it  is 
the  artery  of  supply  to  the  tongue.  It  has  already  been 
dissected  in  the  carotid  triangle  and  the  submaxillary  region, 
and   the    details  of   its  course  and    relations    are    given    on 

PP-  233.  291. 

Arteria  Maxillaris  Externa  (O.T.  Facial  Artery). — The  ex- 
ternal maxillary  artery  can  be  studied,  at  the  present  stage  of 
the  dissection,  from  its  origin  up  to  the  point  where  it  mounts 
upon  the  mandible  to  reach  the  face.  This  is  termed  the 
cervical  part  oi  the  artery.  It  springs  from  the  anterior  aspect 
of  the  external  carotid,  immediately  above  the  lingual,  in 
the  upper  part  of  the  carotid  triangle,  and  passes  vertically 
upwards,  on  the  lateral  surface  of  the  middle  constrictor 
muscle  of  the  pharynx,  to  the  angle  of  the  mandible,  w^here 
it  disappears  under  cover  of  the  posterior  belly  of  the 
digastric  and  the  stylo-hyoid  muscle.  At  this  point  the 
superior  constrictor  is  medial  to  it  and   separates  it  from  the 


298 


HEAD  AND  NECK 


lateral  surface  of  the  tonsil.  At  the  upper  border  of  the 
stylo-hyoid  it  enters  a  deep  groove  in  the  posterior  end  of 
the  submaxillary  gland.  Emerging  from  this  it  turns  down- 
wards and  anteriorly  between  the  lateral  surface  of  the  gland 


Superficial  temporal 

Frontal  branch  of 
li^ophthalmic  artery 
m.    ^Supra-orbital  branch  of 
ophthalmic  artery- 
Middle  temporal 

Transverse  facial 

Angular 
Lateral  nasal 

Infra-orbital 
Superior  labial 

Inferior  labial 

(O.T.  inferior 
labial.)     See  p.  131 


External  maxillary 
Fig.  119. — Arteries  of  the  Face 


Buccinator  branch  of  internal  maxillary 


and  the  internal  pterygoid  muscle,  and  turning  round  the  lower 
border  of  the  mandible  at  the  anterior  border  of  the  masseter 
it  enters  the  face.  For  details  of  its  facial  course  see  p.  129. 
Four  named  branches  spring  from  the  external  maxillary 
artery  in  the  cervical  part  of  its  course  : — 


GREAT  VESSELS  AND  NERVES  OF  NECK     299 


1.  Ascending  palatine. 

2.  The  tonsillar. 


3.  Glandular. 

4.  The  submental. 


Arteria    Palatina    Ascendens. — The  ascending     palatine 

branch   is   given  off  for  the   supply  of  the   soft  palate,  but 

it     distributes    branches    to    the    tonsil  and   auditory    (O.T. 

Eustachian)    tube    also.       It    ascends  between    the    stylo- 


Superficial 
temporal  artery 
Internal  maxil- 
lary artery 

Posterior  auricu- 
lar artery 

External  carotid 


Occipital  artery 

Sterno-mastoid  arterj' 

Hj'poglossal  nerve 

Ascending  phar^mgeal  artery 


Submental 

artery 
External  maxillary 
artery 


Internal  carotid  artery 
Descendens  hypoglossi 

Superior  thy'reoid  artery- 
Sterno-mastoid  artery 


Inferior  hyoid  artery 

J|^|^§~^ Internal  laryngeal  artery 
Prominentia  laryngea 


Sterno-hyoid 


Common  carotid  artery 


Omo-hyoid 


Fig.  120. — Diagram  of  the  External  Carotid  Artery  and 
its  Branches. 


pharyngeus  and  stylo-glossus  muscles,  and  will  be  seen  when 
the  styloid  process  is  reflected. 

Ra?fius  Tonsillaris. — The  tonsillar  branch  runs  upwards 
between  the  internal  pterygoid  and  stylo-glossus  muscles,  then 
turns  medially,  pierces  the  superior  constrictor,  and  enters 
the  tonsil. 

The  glandular  branches  are  given  to  the  submaxillary 
gland  as  the  external  maxillary  artery  passes  through  it. 


300  HEAD  AND  NECK 

Arteria  Submentalis. — This  is  a  branch  of  some  size.  It 
arises  close  to  the  base  of  the  mandible,  and  runs  towards 
the  chin  upon  the  mylo-hyoid  muscle.  Near  the  symphysis 
it  changes  its  direction,  and  is  carried  upwards  over  the  border 
of  the  mandible,  to  end  in  branches  for  the  muscles  and 
integument  of  the  chin  and  lower  lip.  In  the  submaxillary 
region  it  gives  numerous  twigs  to  the  surrounding  muscles 
and  glands,  and  anastomoses  with  the  sublingual  artery  by 
branches  which  pierce  the  mylo-hyoid  muscle.  It  anasto- 
moses, in  the  face,  with  the  inferior  labial  branch  of  the 
external  maxillary  and  the  mental  branch  of  the  inferior 
alveolar. 

Vena  Facialis  Anterior. — The  cervical  portion  of  the 
anterior  facial  has  already  been  seen  (p.  23 1)  passing  posteriorly 
and  downwards,  superficial  to  the  submaxillary  gland.  After 
receiving  tributaries  corresponding  to  the  branches  of  the 
similar  part  of  the  external  maxillary  artery,  it  joins  the 
posterior  facial  vein.  The  short  trunk  thus  formed  is  termed 
tYiQ  common  facial  vein,  and  it  pours  its  blood  into  the  internal 
jugular  at  the  level  of  the  hyoid  bone. 

Arteria  Occipitalis. — The  occipital  artery  springs  from  the 
posterior  aspect  of  the  external  carotid  at  the  same  level  as 
the  external  maxillary.  It  takes  the  lower  border  of  the 
posterior  belly  of  the  digastric  muscle  as  its  guide,  and  runs 
upwards  and  posteriorly,  under  cover  of  the  sterno-mastoid 
muscle,  and  generally  under  cover  of  the  lower  border  of  the 
posterior  belly  of  the  digastric,  to  reach  the  interval  between 
the  mastoid  portion  of  the  base  of  the  skull  and  the  transverse 
process  of  the  atlas.  Thence  onwards  it  has  been  studied 
in  the  dissection  of  the  scalp  and  the  back  of  the  neck 
(pp.  162,  170).  The  first  part  of  the  vessel  crosses  the  internal 
carotid  artery,  the  vagus  nerve,  the  accessory  nerve,  and  the 
internal  jugular  vein,  whilst  the  hypoglossal  nerve  hooks 
round  it. 

The  only  branches  which  spring  from  this  portion  of  the 
occipital  are:  (i)  muscular  twigs;  and  (2)  a  meningeal 
branch. 

The  muscular  twigs  are  given  to  the  neighbouring  muscles, 
and  one  of  them,  larger  than  the  others  and  very  constant,  is 
termed  the  sterno-mastoid  bra?ich,  runs  parallel  with  the 
accessory  nerve,  and  sinks  with  it  into  the  substance  of 
the  sterno-mastoid  muscle. 


GREAT  VESSELS  AND  NERVES  OF  NECK     301 

A  77ieningeal  branch  associates  itself  with  the  internal 
jugular  vein,  and  can  be  followed  upwards  upon  it  to 
the  jugular  foramen,  through  w^hich  it  passes  into  the 
cranium. 

Arteria  Auricularis  Posterior. — The  posterior  auricular 
artery  will  be  found  above  the  level  of  the  posterior  belly  of 
the  digastric,  and,  like  the  occipital,  it  takes  origin  from  the 
posterior  aspect  of  the  external  carotid  artery.  In  the  first 
part  of  its  course  it  is  placed  deeply,  and  runs  upwards  and 
posteriorly  betw^een  the  styloid  process  of  the  temporal  bone 
and  the  postero-medial  surface  of  the  parotid  gland  to  reach 
the  interval  between  the  mastoid  process  and  the  back  of 
the  auricle.  Then  it  joins  the  posterior  auricular  nerve. 
Its  further  course  has  been  studied  in  the  dissection  of  the 
scalp  (p.  157). 

This  portion  of  the  posterior  auricular  artery  gives  off 
(i)  muscular  twigs  ;  (2)  a  few  branches  to  the  parotid  gland; 
and  (3)  the  stylo-mastoid  artery. 

Arteria  Stylomastoidea. — This  is  a  slender  vessel  which 
enters  the  stylo-mastoid  foramen.  In  the  interior  of  the  tem- 
poral bone  it  has  an  extensive  distribution.  It  supplies  twigs 
to  the  mastoid  cells  and  to  the  tympanic  cavity  and  is  carried 
onwards  in  the  canalis  facialis  (O.T.  Fallopian)  to  anastomose 
with  the  petrosal  branch  of  the  middle  meningeal. 

Arteria  Maxillaris  Interna. — The  commencement  of  the 
internal  maxillary  artery,  from  the  termination  of  the  external 
carotid,  between  the  neck  of  the  mandible  and  the  antero- 
medial  surface  of  the  parotid  gland,  has  been  seen  already,  and 
the  artery  has  been  traced  through  the  infratemporal  region 
to  the  pterygo-palatine  fossa,  where  its  terminal  branches  will 
be  dissected  at  a  later  period. 

Arteria  Temporalis  Superficialis.  —  Like  the  internal 
maxillary,  this  artery  commences  between  the  neck  of  the 
mandible  and  the  antero-medial  surface  of  the  parotid  gland. 
It  passes  upwards  and,  as  it  emierges  from  under  cover  of 
the  upper  end  of  the  parotid,  it  crosses  the  posterior  end 
of  the  zygomatic  arch  and  enters  the  superficial  fascia  of  the 
scalp,  in  which  it  ascends  on  the  superficial  surface  of  the 
temporal  fascia,  and  anterior  to  the  auricle  it  breaks  up 
into  two  branches,  frontal  and  parietal.  These  anastomose 
with  each  other  and  with  their  fellows  of  the  opposite 
side.     The  frontal   anastomoses   with   the   supra-orbital   and 


302 


HEAD  AND  NECK 


frontal  branches  of  the  ophthalmic  also,  and  the  parietal 
with  the  posterior  auricular  and  the  occipital  arteries.  Whilst 
it  is  still  under  cover  of  the  parotid  it  gives  branches  to  the 


Superficial 
temporal  arteries 
Zygomatico- 
temporal nerve 

Auriculo-temporal 
nerve 


Parotid 


Facial  net 
Poster    I 
auricu' 
DigasLiiv. 
Occipital  artery 

Great  auricular 

Internal  carotid 

External  carotid 

External  jugular  vein 

Nervus  cutaneus 

colli 

Communicans 

cervicalis 

Sterno-mastoid 


Fig.  121.- 


-^     Parotid  duct 
Transverse  facial 

Buccinator 


Masseter 
Ext.  maxillary  artery  and 
\  anterior  facial  vein 

Submaxillary  gland 
Hypoglossal  nerve 
Ij   \       Lingual  artery 

Superior  thyreoid  artery 
Thyreo-hyoid  muscle 
Ansa  hypoglossi 


-Dissection  of  the  Parotid  Region  and  the  upper  part  of  the 
Anterior  Triangle  of  the  Neck. 


gland  ;  anterior  auricular  branches Xo  the  auricle ;  the  transverse 
facial^  which  passes  along  the  lower  border  of  the  zygomatic 
arch  across  the  masseter.  As  the  superficial  temporal  crosses 
the  zygoma  it  gives  off  a  zygojnatico-orbitai  branch,  which  runs 
to    the   lateral    border   of   the   orbit,   and   a   middle  temporal 


GREAT  VESSELS  AND  NERVES  OF  NECK     303 

branchy  which  perforates  the  temporal  fascia  and  anastomoses 
in  the  temporal  fossa  with  the  deep  temporal  branches  of  the 
internal  maxillary.  The  course  of  this  branch  and  also  the 
distribution  of  the  terminal  branches  have  been  followed  in 
earlier  stages  of  the  dissection  (pp.  266,  267). 

Dissection. — Divide  the  posterior  belly  of  the  digastric  immediately 
below  its  origin,  and  turn  it  downwards  and  anteriorly  towards  the  hyoid 
bone  ;  then  examine  the  stylo-pharyngeus  muscle.  It  may  be  necessary  to 
cut  the  occipital  and  posterior  auricular  arteries  in  order  to  gain  free  access 
to  the  deeper  parts,  but  this  should  not  be  done  unless  it  is  necessary. 
Care  must  be  taken  whilst  cleaning  the  stylo-pharyngeus  to  avoid  injuring 
the  glosso-pharyngeal  nerve,  which  turns  round  its  posterior  border  and 
crosses  its  superficial  surface. 

Musculus  Stylopharyngeus. — This  is  the  longest  of  the 
three  slender  muscles  which  spring  from  the  styloid  process. 
It  arises  from  its  deep  or  medial  surface  close  to  its  root,  and 
extends  downwards  and  anteriorly  to  gain  the  side  of  the 
pharynx,  where  it  disappears  under  cover  of  the  upper  border 
of  the  middle  constrictor  muscle.  Whilst  under  cover  of 
the  middle  constrictor  its  fibres  blend  with  those  of  the  palato- 
pharyngeus,  and,  with  these,  are  inserted  into  the  posterior 
border  of  the  corresponding  lamina  of  the  thyreoid,  cartilage. 
Some  of  the  fibres,  however,  are  lost  in  the  wall  of  the  pharynx. 
If  the  dissector  removes  the  fascia  at  the  posterior  part  of 
the  thyreo-hyoid  space  he  will  expose  the  lower  fibres  of  the 
middle  and  the  upper  fibres  of  the  inferior  constrictor,  and 
in  the  interval  between  them,  on  a  deeper  plane,  the  lateral 
surface  of  the  lower  part  of  the  stylo-pharyngeus. 

Dissection. — Snip  through  the  base  of  the  styloid  process  with  the  bone 
forceps,  and  throw  it  and  the  attached  muscles  downwards  and  anteriorly. 
The  upper  parts  of  the  internal  carotid  artery  and  the  internal  jugular  vein 
are  now  exposed,  and  the  ascending  pharyngeal  artery  can  be  followed  to 
the  base  of  the  skull. 

Arteria  Pharyngea  Ascendens. — To  expose  this  vessel  the 
dissector  must  push  the  external  carotid  anteriorly  and  clean 
the  interval  between  it  and  the  internal  carotid.  The 
ascending  pharyngeal  springs  from  the  medial  surface  of  the 
external  carotid  close  to  its  lower  end  and  is  its  smallest 
branch.  It  ascends  along  the  lateral  border  of  the  pharynx, 
lying  between  the  stylo-pharyngeus  laterally  and  the  con- 
strictors of  the  pharynx  medially,  first  in  a  plane  between  the 
external  and  internal  carotid  arteries,  and  then  to  the  medial 
side  of  the  internal  carotid.     As  it  passes  upwards  it  gives 


304  HEAD  AND  NECK 

pharyngeal  branches  to  the  wall  of  the  pharynx  and 
prevertebral  branches  to  the  prevertebral  muscles.  At 
the  base  of  the  skull  it  gives  off  meningeal  branches^  which 
enter  the  cranial  cavity  through  the  hypoglossal  canal,  the 
jugular  foramen,  and  the  foramen  lacerum ;  and  palatine 
branches^  which  pierce  the  pharyngeal  aponeurosis  above  the 
upper  border  of  the  superior  constrictor  and  descend,  along 
the  levator  palati,  to  the  soft  palate.  Offsets  from  these 
branches  are  given  to  the  auditory  tube  (O.T.  Eustachian) 
and  to  the  tonsil. 

Dissection. — After  the  ascending  pharyngeal  artery  has  been  examined, 
the  internal  carotid  artery,  the  glossopharyngeal,  vagus,  accessory,  and 
hypoglossal  nerves,  and  the  superior  cervical  ganglion,  with  their  various 
connections  and  branches,  must  be  dissected.  A  dense  and  tough  fascia 
envelops  these  structures,  and  a  great  amount  of  patience  is  required  to 
trace  the  branches  of  the  nerves  through  it.  One  nerve — the  pharyngeal 
branch  of  the  vagus — which  proceeds  downwards  and  anteriorly  upon  the 
superficial  or  lateral  aspect  of  the  internal  carotid,  is  especially  liable  to 
injury,  and  must  therefore  be  borne  in  mind  from  the  very  outset  of 
the  dissection.  The  internal  laryngeal  and  the  external  laryngeal  nerves 
have  been  previously  displayed  in  the  anterior  triangle  of  the  neck.  These, 
if  traced  upwards,  will  lead  to  the  superior  laryngeal  branch  of  the  vagus, 
which  lies  in  relation  with  the  deep  aspect  of  the  internal  carotid  artery. 
Near  the  base  of  the  skull  all  the  nerve-trunks  will  be  found  making 
their  appearance,  close  together,  in  the  interval  between  the  internal 
jugular  vein  and  the  internal  carotid  artery  ;  whilst  posterior  to  the  vein 
the  rectus  lateralis  muscle  and  the  first  loop  of  the  cervical  plexus  will  be 
seen. 

Arteria  Carotis  Interna. — The  internal  carotid  artery  is 
one  of  the  two  terminal  branches  of  the  common  carotid, 
and  it  commences  at  the  level  of  the  upper  border  of  the 
thyreoid  cartilage.  From  this  point  it  proceeds  upwards 
in  the  neck,  in  a  vertical  direction,  until  it  reaches  the 
base  of  the  skull;  there  it  disappears  from  view  by  entering 
the  carotid  canal  of  the  petrous  portion  of  the  temporal 
bone,  through  which  it  reaches  the  interior  of  the  cranium. 
The  internal  carotid  artery  can  therefore  be  very  appropri- 
ately divided  into  three  parts — viz.  (i)  a  cervical ;  (2) 
a  petrous ;  and  (3)  an  intracranial.  The  cervical  part 
alone  comes  under  the  notice  of  the  student  in  the  present 
dissection. 

In  the  first  part  of  its  extent  the  internal  carotid  artery 
lies  in  the  carotid  triangle,  and  is  therefore  comparatively 
superficial.  It  is  covered  by  the  integument,  platysma,  and 
fascia,  and  is  overlapped  by  the  sterno-mastoid  muscle  and 


GREAT  VESSELS  AND   NERVES  OF  NECK     305 

the  anterior  border  of  the  internal  jugular  vein ;  it  is  crossed 
by  the  hypoglossal  nerve  and  the  sterno-mastoid  branch  of  the 
occipital  artery,  the  lingual  and  common  facial  veins  ;  and  the 


Accessory 


-Vagus 

-Jugular  ganglion 


Ganglion 
nodosum 

Pharyngeal 
branch 


Superior  laryngeal 


Hypoglossal 


Descendens  hypoglossi 


Ascending  pharyngeal 


Internal  carotids 


— GlosFO-pharyngeal 
-Superficial  temporal 

Internal  maxillary 


External 
carotid 

Posterior 
auricular 

Occipital 


External 
maxillary 

Lingual 

Branch  to 
thyreo-hyoid 
Internal 
laryngeal 


External 
laryngeal 


Common  carotid 


Fig.  122. — Diagram  of  Carotid  System  of  Vessels  in  the  Neck  with  the 
Glosso-pharyngeal,  Vagus,  Accessory,  and  Hypoglossal  Nerves. 


descendens  hypoglossi  descends  on  its  superficial  surface.  As 
it  proceeds  upwards,  it  comes  to  lie  under  cover  of  the  lower 
end  of  the  parotid  gland,  and  then  at  a  higher  level  under 
cover  of  the  posterior  belly  of  the  digastric,  the  stylo-hyoid, 
VOL.  II — 20 


3o6 


HEAD  AND  NECK 


the  stylo-pharyngeus,  and  the  styloid  process,  which  separate 
it  from  the  postero-medial  surface  of  the  parotid  gland.  It 
will  be  noted  also  that  three  nerves  and  two  arteries  cross  the 
vessel  superficially,  viz.  : — 


1.  The  occipital  artery. 

2.  The  posterior  auricular  artery. 


1.  The  hypoglossal  nerve. 

2.  The  glosso-pharyngeal  nerve. 

3.  The    pharyngeal   branch    of    the 

vagus  nerve. 

The  hypoglossal,  as  already  noted,  crosses  it  in  the  carotid 
triangle  ;  the  other  nerves  cross  it  under  cover  of  the  posterior 


Thyreo-hyoid  membrane 
Plica  vocalis 
Processus  vocalis 
Arytaenoid  cartilage 

Platys 
Posterior  wall 
of  pharynx 
Retropharyn 
geal space 

Carotid  sheatb 


Sterno-hyoid 

Thyreo-hyoid 

Thyreoid  cartilage 
^.      Omo-hyoid 
^C^<s<C       Recessus  piriformis 
Superior  thyreoid 
X      Descendens 
^/  hj'poglossi 

Common  carotid 
Internal  jugular 

_  Vagus 


Scalenus  anterior^  /  /  ^  Sympathetic  trunk 

Longus  colli  Vertebral  artery 

Fig.   123. — Transverse  section  through  the  Neck  at  the  level  of  tipper 
part  of  Thyreoid  Cartilage. 

belly  of  the  digastric.  The  occipital  artery  crosses  it  at  the 
level  of  the  lower  border  of  the  posterior  belly  of  the  digastric, 
and  the  posterior  auricular  at  the  level  of  its  upper  border. 

The  relationship  of  the  external  carotid  artery  to  the 
internal  carotid  is  a  varying  one.  At  first  the  external 
carotid  lies  antero-medial  to  it ;  but  soon,  owing  to  its  in- 
clination posteriorly,  it  comes  to  lie  directly  superficial  to  the 
internal  carotid.  The  following  structures  intervene  between 
the  two  vessels  : — 


1.  Styloid  process. 

2.  Stylo-pharyngeus  muscle. 

3.  Glosso-pharyngeal  nerve. 


of 


vagus 


4.  Pharyngeal   branches 

and  sympathetic. 

5.  A  portion  of  the  parotid  gland 


Posterior  to  the  internal  carotid  is  the  longus  capitis  (O.T. 
rectus  capitis  anticus  major)  and  the  sympathetic  trunk ; 
postero-laterally  are  the  glosso-pharyngeal,  the  vagus,  the 
accessory  and  the  hypoglossal  nerve  \  and  still  more  laterally 


GREAT  VESSELS  AND  NERVES  OF  NECK    307 

and  posteriorly  is  the  internal  jugular  vein.  On  its  medial 
aspect  the  internal  carotid  is  related  to  the  pharynx,  the 
ascending  pharyngeal  artery  and  the  levator  veli  palatini. 

Before  leaving  this  vessel,  note  that  near  the  base  of  the 
skull  four  nerves  appear  in  the  interval  between  it  and  the 
internal  jugular  vein;  these  are  the  glosso -pharyngeal,  the 
vagus,  the  accessory,  and  the  hypoglossal. 

Vena  Jugularis  Interna.— The  internal  jugular  vein  is  the 
largest  venous  channel  of  the  neck.  It  enters  the  neck  through 
the  posterolateral  compartment  of  the  jugular  foramen,  where 
it  is  directly  continuous  with  the  transverse  sinus  of  the  cranial 
cavity.  From  the  jugular  foramen  it  proceeds  downwards, 
until  it  reaches  the  posterior  aspect  of  the  medial  end  of 
the  clavicle,  where  it  joins  the  subclavian  vein  to  form  the 
innominate  vein.  Its  commencement  in  the  jugular  foramen 
shows  a  slight  dilatation,  termed  the  bulb,  the  lumen  of  which 
remains  at  all  times  patent  owing  to  the  connection  of  its 
walls  to  the  margins  of  the  foramen.  The  skull  cap  should 
be  removed  and  a  probe  should  be  passed  from  the  trans- 
verse sinus  into  the  internal  jugular  vein,  to  demonstrate  the 
continuity  of  the  two  channels. 

Relations.— hX  its  commencement  the  internal  jugular 
vein  lies  postero-lateral  to  the  upper  end  of  the  cervical 
part  of  the  internal  carotid  artery,  from  which  it  is  partially 
separated  by  the  last  four  cerebral  nerves.  As  it  descends 
it  assumes  a  more  directly  lateral  relationship,  first  to  the 
internal  and  then  to  the  common  carotid,  overlapping  each 
vessel  to  a  slight  extent  anteriorly ;  and  it  is  enclosed  with  them 
and  the  vagus  nerve  in  a  common  sheath  of  deep  cervical 
fascia,  the  nerve  lying  in  its  own  compartment  of  the  sheath 
between  the  arteries  medially  and  the  vein  laterally,  and  in  a 
posterior  plane. 

The  superficial  or  lateral  relations  of  the  vein  m  the  upper 
part  of  its  extent  are  the  styloid  process,  with  the  stylo- 
pharyngeus  and  stylo-hyoid  muscles,  and  the  posterior  belly 
of  the  digastric,  which  separate  it  from  the  upper  part  of  the 
postero-medial  surface  of  the  parotid  gland.  In  this  part 
of  its  extent  it  is  crossed  superficially,  along  the  upper  border 
of  the  posterior  belly  of  the  digastric,  by  the  posterior 
auricular  artery,  and  at  the  lower  border  of  the  digastric 
by  the  accessory  nerve,  passing  downwards  and  posteriorly, 
and  by  the  occipital  artery  passing  upwards  and  posteriorly 
11—20  a 


3o8 


HEAD  AND  NECK 


superficial  to  the  nerve.  At  a  slightly  lower  level  it  is  con- 
cealed by  the  lower  part  of  the  postero-medial  surface  of  the 
parotid,  and  it  is  crossed  by  the  sterno-mastoid  branch  of  the 
occipital  artery.  After  it  emerges  from  under  cover  of  the 
parotid,  it  lies  under  cover  of  the  anterior  border  of  the 
sterno-mastoid,  except  in  the  region  of  the  upper  part  of  the 
carotid  triangle,  where  it  may  project  anteriorly,  beyond  the 
anterior  border  of  the  muscle,  for  a  short  distance.  It  is 
separated  from  the  sterno-mastoid  by  numerous  deep  cervical 
lymph  glands ;  and  under  cover  of  the  muscle  it  is  crossed 
superficially,  at  the  level  of  the  upper  part  of  the  thyreoid 


Sheath  of  dura  mater 

around  vagus  and 

accessory  nerves 


Ganglion  nodosum 

Internal  jugular  vein 

Superior  laryngeal  nerve 

Accessory  nerve 


Vagus  nerve 


Sheath  of  dura  mater  around 
glosso-pharyngeal  nerve 

Inferior  petrosal  sinus 
Internal  carotid  artery 

Glosso-pharyngeal  nerve 


Pharyngeal  branch  of 
vagus 


Internal  laryngeal  nerve 
External  laryngeal  nerve 


Fig.  124. — Diagram  of  the  relation  of  parts  in  the 
Jngular  Foramen. 

cartilage,  by  the  communicans  cervicalis  from  the  cervical 
plexus,  and,  at  the  level  of  the  cricoid  cartilage,  by  the 
intermediate  tendon  of  the  omo-hyoid,  the  sterno-mastoid 
branch  of  the  superior  thyreoid  artery  and  the  nerve  to  the 
posterior  belly  of  the  omo-hyoid.  Below  the  omo-hyoid  it 
is  covered  by  the  posterior  border  of  the  sterno-hyoid,  and  is 
crossed  by  the  anterior  jugular  vein ;  and  at  its  termination 
it  lies  posterior  to  the  sternal  end  of  the  clavicle. 

Posteriorly,  it  is  in  relation  with  the  rectus  capitis  lateralis  ; 
the  rectus  capitis  anterior  (O.T.  anticus  minor) ;  and  the  loop 
between  the  first  and  second  cervical  nerves.  At  a  lower 
level  its  posterior  relations  are  the  transverse  processes  of  the 
cervical  vertebrse  and  the  muscles  attached  to  their  anterior 
tubercles,  viz.,  the  longus  capitis  (O.T.  rectus  capitis  anticus 


GREAT  VESSELS  AND  NERVES  OF  NECK     309 

major)  and  the  scalenus  anterior.  Between  its  posterior 
surface  and  the  scalenus  anterior  are  the  ascending  cervical 
artery,  the  phrenic  nerve,  and,  crossing  superficial  to  the  latter, 
the  transverse  cervical  and  the  transverse  scapular  arteries. 
On  the  left  side  the  terminal  part  of  the  thoracic  duct  also 
crosses  the  phrenic  nerve  posterior  to  the  internal  jugular  vein. 
At  the  medial  border  of  the  scalenus  anterior  the  thyreo- 
cervical  artery  is  posterior  to  it,  and  at  a  lower  level,  the 
first  part  of  the  subclavian  artery  and  the  dome  of  the  pleura. 

The  right  vein  is  usually  the  larger  of  the  two ;  and  as 
they  approach  the  root  of  the  neck  both  veins  incline  slightly 
to  the  right,  with  the  result  that,  on  the  right  side,  the  lower 
part  of  the  vein  is  separated  from  the  common  carotid  artery 
by  a  small  triangular  interval  bounded  below  by  the  subclavian  * 
artery,  whilst  on  the  left  side  the  vein  overlaps  the  anterior 
aspect  of  the  common  carotid  artery. 

Ti'ibutaries. — Immediately  below  its  commencement  the 
internal  jugular  vein  is  joined  by  the  inferior  petrosal  sinus, 
and  then,  successively,  by  offsets  from  the  pharyngeal  plexus, 
by  the  lingual  vein,  the  common  facial  vein,  the  superior  and 
middle  thyreoid  veins.  In  some  cases  it  is  joined  near  its 
upper  end  by  a  vena  conies  which  runs  with  the  occipital 
artery ;  and,  occasionally,  near  its  lower  end,  it  receives  the 
lymph  trunks  which  usually  open  into  the  commencement 
of  the  innominate  vein. 

Dissection. — Slit  open  the  lower  part  of  the  vein  and  examine  the  valve 
which  lies  close  to  its  extremity.  It  consists  of  two  or  three  semilunar 
flaps  which  prevent  regurgitation  of  blood  from  the  innominate  vein  into 
the  internal  jugular.  > 

Nervi  Glosso-pharyngeus,  Vagus,  Accessorius.  —  After 
the  removal  of  the  brain  these  nerves  were  seen  leaving 
the  cranial  cavity  through  the  middle  compartment  of  the 
jugular  foramen  in  the  interval  between  the  com.mencement 
of  the  internal  jugular  vein  postero-laterally  and  the  inferior 
petrosal  sinus  antero-medially  (p.  215,  and  Fig.  125,  p.  310). 
The  dissector  should  again  examine  the  interior  of  the  cranial 
cavity  and  refresh  his  memory  as  to  the  manner  in  which 
they  enter  the  foramen.  The  glosso-pharyjigeal  occupies 
the  most  anterior  position,  and  it  is  cut  off  from  the  others 
by  a  separate  tube-like  sheath  of  dura  mater.  The  accessory 
is  placed  posterior  to  the  vagus,  and  both  are  included 
within  the  same  sheath  of  dura  mater.  They  therefore 
11—20  h 


3IO 


HEAD  AND  NECK 


traverse  the  foramen  in  close  contact  with  each  other. 
Reaching  the  exterior  of  the  skull,  the  three  become 
associated  with  the  hypoglossal  nerve ;  and  the  four  nerves 
lie  for  a  short  distance  in  the  interval  between  the  internal 
jugular  vein  and  the  internal  carotid  artery,  but  soon  they 
choose  different  routes.  The  accessory  inclines  posteriorly, 
superficial  or  deep  to  the  internal  jugular  vein ;  the  glosso- 
pharyngeal runs  anteriorly,  superficial  to  the  internal  carotid. 


Oculo-motor  nerve 


Trochlear  nerve 

Sensory  root  of  the  trigeminal  nerve 
Motor  root  of  the  trigeminal 
nerve 

Abducent  nerve 

Motor  root  of  facial 
nerve 

Cut  edge  of  the 
tentorium 


'—Sensory  root  of 

facial  nerve 
Acustic  nerve 

Right  transverse 
sinus 
Glosso-pharyngeal 
nerve 
Vagus  nerve 

Accessory  nerve 

^~^ Vertebral  artery 
Hypoglossal  nerve 
f  irst  spinal  nerve 
Accessory  nerve 


Fig.  125. — Section  through  the  Head  a  little  to  the  right  of  the  Median  Plane. 
It  shows  the  posterior  cranial  fossa  and  the  upper  part  of  the  vertebral 
canal  after  the  removal  of  the  brain  and  the  medulla  spinalis. 


and  under  cover  of  the  posterior  belly  of  the  digastric  ;  at 
a  lower  level  the  hypoglossal  turns  anteriorly  across  the 
external  and  internal  carotid  arteries  ;  and  the  vagus  proceeds 
vertically  downwards,  first  between  the  internal  jugular  vein 
and  the  internal  carotid,  and  then  between  the  vein  and  the 
common  carotid  (Fig.  100). 

In  an  ordinary  dissection  it  is  impossible  to  follow  out  many  of  the 
minute  twigs  which  take  origin  from  these  nerves  in  the  region  of  the 
basis  cranii.  To  do  so  it  is  necessary  to  possess  a  perfectly  fresh  part 
which  has  been  specially  prepared  by  having  the  soft  parts  toughened  with 
spirit  and  the  bone  softened  by  immersion  in  a  weak  solution  of  acid. 


GREAT  VESSELS  AND  NERVES  OF  NECK    311 

Even  then  the  dissection  is  a  difficult  one,  although  it  should  certainly  be 
undertaken  by  the  advanced  student,  in  the  event  of  his  being  able  to  obtain 
a  part  for  the  purpose. 

In  the  following  description  of  these  nerves  the  account 
of  the  branches  which  can  in  all  cases  be  traced  is  printed  in 
ordinary  type,  whilst  that  of  those  requiring  special  dissection 
is  printed  in  small  type. 

Nervus  Glosso-pharyngeus. — The  glosso-pharyngeal  nerve 
inclines  downwards  and  anteriorly  and  crosses  the  internal 
carotid  artery  superficially.  At  first  it  lies  medial  to  the 
styloid  process  and  the  stylo  -  pharyngeus  muscle,  then  it 
hooks  round  the  lower  border  of  the  muscle  and  curves 
anteriorly  upon  its  superficial  surface  to  gain  the  base  of 
the  tongue.  In  the  dissection  of  the  submaxillary  region, 
its  terminal  part  was  seen  disappearing  under  cover  of  the 
hyoglossus  muscle,  where  it  ends  in  lingual  branches. 

In  the  present  dissection  the  following  branches  should  be 
made  out : — 


1.  Communicating   branch    from 

the  facial. 

2.  Nerve  to  the  stylo-pharyngeus. 


3.  Pharyngeal. 

4.  Tonsillitic. 

5.  Lingiial. 


The  communicating  branch  from  the  facial  springs  from  the  nerve  to 
the  posterior  belly  of  the  digastric,  and,  as  a  rule,  emerges  from  midst  the 
fibres  of  that  muscle  to  join  the  glosso-pharyngeal  close  to  the  lower  part  of 
the  jugular  foramen. 

The  stylo-pharyngeal  nerve  is  a  small  twig  which  enters  the 
muscle  of  the  same  name.  The  greater  part  of  its  fibres, 
however,  are  continued  through  the  muscle  to  the  mucous 
membrane  of  the  pharynx. 

The. pharyngeal  branches  consist — (i)  of  one  or  two  small 
twigs  which  perforate  the  superior  constrictor  to  reach  the 
mucous  membrane  of  the  pharynx ;  and  (2)  a  larger  nerve 
which  comes  off  higher  up  and  passes  with  the  pharyngeal 
branch  of  the  vagus  to  the  pharyngeal  plexus.  It  frequently 
divides  into  two  or  more  branches. 

The  tonsillitic  branches  proceed  from  the  glosso-phar}^ngeal 
near  the  base  of  the  tongue.  They  form  a  plexus  over  the 
tonsil,  termed  the  circulus  tonsillaris.,  and  give  twigs  to  the 
mucous  membrane  of  the  isthmus  faucium  and  the  soft 
palate. 

The  terminal  or  li?igiml  branches  will  be  followed  in  the 
dissection  of  the  tongue. 

11—20  c 


312  HEAD  AND  NECK 

There  are  still  other  points  in  connection  with  the  glosso-pharyngeal 
nerve  which  require  mention.  At  the  lower  part  of  the  jugular  foramen 
two  small  ganglia  are  formed  upon  its  trunk,  and  from  the  lower  of  these 
certain  minute  branches  are  given  off.  The  upper  ganglion  is  called  the 
ganglion  superucs ;  the  lower  one  is  termed  the  ganglion  petrosum. 

The  superior  ganglion  is  a  small  ganglionic  swelling,  which  involves 
only  a  portion  of  the  fibres  of  the  nerve  trunk.  It  is  placed  in  the 
upper  part  of  the  bony  groove  in  which  the  nerve  lies  as  it  proceeds  through 
the  jugular  foramen.     No  branches  arise  from  it. 

The  petrous  ganglion  is  a  larger  swelling,  which  involves  the  entire 
nerve-trunk,  and  lies  at  the  opening  of  the  jugular  foramen,  between  the 
vagus  nerve  and  the  inferior  petrosal  sinus  (which  intervenes  between  it 
and  the  anterior  border  of  the  foramen).  Its  length  is  not  more  than  two 
or  three  lines.  Three  branches  of  communication  enter  or  proceed  from  it. 
These  connect  it  with — (i)  the  superior  cervical  sympathetic  ganglion ;  (2) 
the  auricular  branch  of  the  vagus ;  and  (3)  the  jugular  ganglion  of  the 
vagus. 

In  addition  to  these  twigs  the  tympanic  nerve  takes  origin  from  the 
petrous  ganglion. 

Tympanic  Nerve. — The  ultimate  destination  of  this  nerve  may  be 
regarded  as  the  otic  ganglion,  but  it  takes  a  very  circuitous  route  to  gain 
that  structure  and  it  gives  off  branches  on  the  way.  It  enters  a  small  foramen 
on  the  ridge  which  separates  the  jugular  fossa  from  the  carotid  foramen 
on  the  lower  surface  of  the  petrous  bone,  and  it  is  conducted  by  a  narrow 
canal  to  the  tympanic  cavity.  It  crosses  the  inner  wall  of  this  chamber, 
grooving  the  promontory.  Having  gained  the  anterior  part  of  the 
tympanum,  it  enters  the  bone  a  second  time,  and  runs  in  a  minute  canal, 
which  tunnels  the  petrous  bone  below  the  upper  end  of  the  channel  in 
which  is  lodged  the  tensor  tympani  muscle.  In  this  part  of  its  course  the 
tympanic  nerve  is  joined  by  a  branch  from  the  ganglion  geniculi  of  the 
facial  nerve,  and,  after  the  junction  is  effected,  it  is  termed  the  small  super- 
ficial petrosal  neT^e. 

The  canal  in  which  the  small  superficial  petrosal  nerve  is  lodged  opens 
into  the  cranial  cavity  upon  the  anterior  surface  of  the  petrous  bone, 
immediately  lateral  to  the  hiatus  canalis  facialis  (O.T.  Fallopii).  Through 
this  the  nerve  emerges,  and  soon  leaves  the  interior  of  the  cranium  by 
passing  downwards  in  the  interval  between  the  great  wing  of  the  sphenoid 
and  the  petrous  part  of  the  temporal  bone,  or  through  the  canaliculus 
innominatus,  or  through  the  foramen  ovale.  Outside  the  skull  it  ends  by 
joining  the  otic  ganglion. 

In  the  tympanic  cavity  the  tympanic  nerve  gives  branches  of  supply 
— (i)  to  the  mucous  membrane  of  the  tympanum;  (2)  to  the  lining 
membrane  of  the  mastoid  cells  ;  and  (3)  to  the  mucous  membrane  of  the 
auditory  tube  (Eustachian).  It  is  connected  with  the  sympathetic  plexus 
on  the  internal  carotid  artery  by  the  superior  and  inferior  carotico -tympanic 
branches  which  pierce  the  substance  of  the  petrous  part  of  the  temporal 
bone. 

Nervus  Vagus. — The  vagus  passes  through  the  middle 
compartment  of  the  jugular  foramen  in  company  with  the 
accessory — both  being  included  within  the  same  sheath  of 
dura  mater.  In  the  neck  it  pursues  a  vertical  course, 
lying,  at  first,  between  the  internal  jugular  vein  and  the 
internal  carotid   artery,    and  afterwards    between    the    same 


GREAT  VESSELS  AND  NERA^ES  OF  NECK    313 

vein  and  the  common  carotid  artery,  enclosed  within  the 
sheath  which  envelops  the  vessels,  but  on  a  plane  posterior 
to  them.  Its  posterior  relations,  therefore,  are  similar  to 
those  of  the  internal  and  common  carotid  arteries.  At  the 
root  of  the  neck  it  enters  the  thorax,  and  has  different 
relations  on  the  two  sides.  On  the  right  side  it  crosses 
the  first  part  of  the  subclavian  artery ;  on  the  left  side,  after 
crossing  anterior  to  the  thoracic  duct,  it  proceeds  downwards 
between  the  common  carotid  and  left  subclavian  arteries, 
posterior  to  the  left  innominate  vein.  For  its  thoracic 
relations  see  p.  99. 

The  vagus,  like  the  glosso-pharyngeal,  has  two  ganglia  in 
connection   with    its   upper  part.       These  are    the   ganglion 
jiigidare  and  the  ganglion  nodosui?i. 

Ganglion  Jugulare  (O.T.  Ganglion  of  Root).^This  is  situated  within  the 
jugular  foramen.  It  is  a  rounded  swelling  which  is  connected  by  com- 
municating twigs  with  several  of  the  nerves  in  the  neighbourhood,  and 
it  gives  off  two  branches  of  distribution. 

Branches  of  Communication. — (i)  With  the  facial  nerve;  (2)  with  the 
petrous  ganglion  of  the  glosso-pharyngeal ;  (3)  with  the  accessory  ;  (4)  with 
the  superior  ganglion  of  the  sympathetic. 

Branches  of  Distribution. — (i)  Meningeal;  (2)  Auricular  nerve. 

The  7neningeal  bi-anch  is  a  minute  twig  which  runs  upwards  through 
the  jugular  foramen,  and,  dividing  into  two  branches,  is  distributed  to 
the  dura  mater  in  the  posterior  cranial  fossa. 

The  atiricular  nerve  (O.T.  Arnold's  nerve)  obtains  a  filament  of  com- 
munication from  the  petrous  ganglion  of  the  glosso-pharyngeal,  and  passes 
posteriorly  upon  the  lateral  surface  of  the  bulb  of  the  internal  jugular  vein 
to  enter  a  minute  aperture  on  the  posterior  part  of  the  lateral  wall  of  the 
jugular  fossa.  A  narrow  canal  then  conducts  it  through  the  substance 
of  the  temporal  bone,  and,  on  its  way,  it  crosses  the  canalis  facialis  a 
short  distance  above  the  stylo-mastoid  foramen.  It  is  thus  brought  into 
close  relation  with  the  facial  nerve  and  is  connected  with  it  by  an 
ascending  and  a  descending  branch  of  communication.  Finally,  it  appears 
on  the  surface  of  the  skull,  in  the  interval  between  the  mastoid  process  and 
the  external  acustic  meatus,  where  it  communicates  with  the  posterior 
auricular  branch  of  the  facial.  It  supplies  the  skin  on  the  posterior  aspect 
of  the  outer  surface  of  the  walls  of  the  meatus,  the  skin  covering  the  lower 
half  of  the  inner  surface  of  the  wall  of  the  meatus,  and  the  lower  half  of 
the  tympanic  membrane. 

Ganglion  Nodosum.  —  After  emerging  from  the  jugular 
foram.en,  the  vagus  nerve  is  joined  by  the  cerebral  portion  of 
the  accessory  nerve,  and  swells  out  into  the  ganglion  nodosum 
(O.T.  ganglion  of  trunk). 

The  ganglion  nodosum  is  an  elongated  reddish-coloured 
swelling  of  about  three-quarters  of  an  inch  in  length,  which 
is    developed   upon   the    stem    of   the    vagus    half  an    inch 


314  HEAD  AND  NECK 

below  the  base  of  the  cranium.  Strong  branches  of  com- 
munication pass  between  it  and  the  first  loop  of  the 
cervical  plexus,  and  the  superior  cervical  ganglion  of  the 
sympathetic.  Further,  the  hypoglossal  nerve  is  generally 
closely  bound  to  it  by  fibrous  attachment,  in  the  midst  of 
which  some  interchange  of  nerve  filaments  takes  place. 

Branches  of  Distribution  of  the  Cervical  Part  of  the 
Vagus. — The  branches  which  spring  from  the  vagus  as  it 
traverses  the  neck  are  the  following:  (i)  pharyngeal; 
(2)  superior  laryngeal ;  (3)  recurrent;  (4)  cardiac. 

Ramus  Pharyngeus.  —  The  pharyngeal  branch  springs 
from  the  upper  part  of  the  ganglion  nodosum  and  runs 
downwards  and  anteriorly,  superficial  to  the  internal  carotid 
artery,  to  end  in  the  pharyngeal  plexus.  It  is  frequently 
replaced  by  two  branches,  of  which  the  upper  is  the  larger. 

Nervus  Laryngeus  Superior. — This,  a  much  larger  branch, 
arises  from  the  middle  of  the  ganglion  nodosum.  It  passes 
downwards  and  anteriorly,  but  differs  from  the  preceding 
nerve  by  passing  deep  to  the  internal  carotid  artery.  In 
this  situation  it  ends  by  dividing  into  the  internal  laryngeal 
and  external  laryngeal  nerves ;  both  of  these  have  been 
previously  seen  in  the  dissection  of  the  anterior  triangle 
(p.  232). 

Before  it  divides,  the  superior  laryngeal  effects  communications  by 
means  of  fine  twigs  with  the  superior  cervical  ganglion  of  the  sympathetic, 
and  it  also  receives  one  or  two  filaments  from  the  pharyngeal  plexus. 

The  internal  laryngeal  nerve  runs  to  the  interval  between 
the  hyoid  bone  and  the  thyreoid  cartilage ;  there,  after 
disappearing  under  cover  of  the  posterior  border  of  the 
thyreo  -  hyoid  muscle,  it  pierces  the  membrane  of  the  same 
name,  and  enters  the  pharynx,  and  then  descends  to  the 
larynx. 

The  external  laryngeal  nerve  is  a  very  slender  branch,  which 
inclines  downwards  and  anteriorly  to  reach  the  crico-thyreoid 
muscle,  in  which  it  ends. 

It  supplies  a  few  filaments  to  the  inferior'constrictor  of  the  pharnyx  and  a 
fine  twig  to  the  superior  cardiac  branch  of  the  sympathetic,  whilst  it 
receives  a  communicating  branch  from  the  superior  cervical  ganglion  of 
the  sympathetic. 

Nervus  Recurrens.  —  The  recurrent  nerve  arises  differ- 
ently on  the  two  sides.     On  the  right  side,  after  springing 


GREAT  VESSELS  AND  NERVES  OF  NECK    315 

from  the  vagus  as  the  latter  crosses  the  first  part  of  the 
subclavian  artery,  it  hooks  round  the  artery  and  ascends  to 
its  termination.  On  the  left  side,  it  arises  in  the  thorax, 
and  hooks  round  the  aortic  arch.  In  the  neck  each  nerve 
ascends  in  the  groove  between  the  trachea  and  oesophagus, 
along  the  medial  side  of  the  lateral  lobe  of  the  thyreoid 
gland,  and,  passing  posterior  or  anterior  to  the  inferior 
thyreoid  artery,  it  disappears  as  the  inferior  laryjigeal  nerve 
under  cover  of  the  lower  border  of  the  inferior  constrictor 
muscle,  and  enters  the  larynx. 

Before  the  recurrent  nerve  reaches  the  larynx  it  gives 
off  several  branches  —  viz.,  (i)  cardiac  branches;  (2)  twigs 
to  the  trachea  and  oesophagus;  and  (3)  a  few  filaments  to  the 
inferior  constrictor  as  it  passes  under  cover  of  its  lower  margin. 

Cardiac  Branches. — Two  cardiac  branches  arise  from  the 
vagus  in  the  neck.  On  the  right  side,  both  of  these  enter 
the  thorax  by  passing  posterior  to  the  subclavian  artery  and 
they  end  in  the  deep  cardiac  plexus.  On  the  left  side,  the  upper 
nerve  joins  the  deep  cardiac  plexus,  whilst  the  lower  nerve 
enters  into  the  formation  of  the  superficial  cardiac  plexus. 

Nervus  Accessorius. — This  nerve  consists  of  two  parts — 
a  spinal  and  a  cerebral.  In  the  foramen  jugulare  the  cerebral 
portion  is  connected  by  one  or  two  fine  twigs  with  the  jugular 
ganglion  of  the  vagus,  and  below  the  basis  cranii  it  leaves 
the  spinal  part  and  joins  the  vagus. 

.  The  cerebral  part  of  the  accessory  nerve  contributes  to  the  vagus 
the  greater  proportion  of  its  motor  fibres.  They  pass  over  the  surface 
of  the  ganglion  nodosum,  and  are  continued  into  the  pharyngeal  and 
into  the  superior  laryngeal  nerves.  Some,  of  the  fibres  are  carried  down 
the  stem  of  the  vagus  into  the  cardiac  branches  and  also  into  the  recurrent 
nerve. 

The  spinal  part  of  the  accessory  is  directed  posteriorly 
under  the  transverse  process  of  the  atlas.  It  crosses  the 
internal  jugular  vein,  and  disappears  into  the  substance 
of  the  sterno-mastoid  muscle.  Its  further  course  has  been 
studied  already  (pp.  147  and  150).  It  is  distributed  to  two 
muscles — viz.,  the  sterno-mastoid  and  the  trapezius. 

Plexus  Pharyngeus. — This  is  a  mesh-work  of  fine 
nerve  filaments,  which  is  formed  upon  the  wall  of  the 
pharynx  at  the  level  of  the  middle  constrictor  muscle. 
The  pharyngeal  branches  of  the  vagus,  glosso-pharyngeal, 
and  superior  cervical  ganglion  of  the  sympathetic  enter  into 


3i6  HEAD  AND  NECK 

its  construction,  and  one  or  more  minute  ganglia  are 
developed  in  connection  with  it.  Its  terminal  twigs  are  given 
to  the  muscles  and  mucous  membrane  of  the  pharynx,  and 
one  branch  (the  ramus  lingualis  vagi)  connects  the  plexus 
with  the  hypoglossal  nerve. 

Nervus  Hypoglossus. —  The  hypoglossal  nerve  makes  its 
exit  from  the  cranium  through  the  canalis  hypoglossi 
(O.T.  anterior  condyloid  foramen).  It  pierces  the  dura  mater 
in  two  separate  parts,  which  unite  into  one  stem  at  the  exit 
of  the  bony  canal.  As  it  issues  from  the  canal  it  hes  deeply, 
medial  to  the  internal  jugular  vein  and  the  internal  carotid 
artery ;  immediately  afterwards  it  inclines  laterally,  and, 
taking  a  half  spiral  turn  around  the  ganglion  nodosum  of  the 
vagus,  it  appears  between  the  two  vessels,  and  descends  between 
them  to  the  lower  border  of  the  posterior  belly  of  the  digastric 
muscle,  where  it  passes  into  the  carotid  triangle.  Its  close 
connection  with  the  ganglion  nodosum  of  the  vagus  has 
been  noted  already  (p.  314).  In  the  carotid  triangle  it  hooks 
round  the  lower  end  of  the  occipital  artery,  below  its  sterno- 
mastoid  branch,  and,  turning  anteriorly,  it  crosses  the  occipital, 
the  internal  and  external  carotid  arteries  and  the  loop  of  the 
lingual  artery  superficially.  Then  it  passes  on  the  medial 
sides  of  the  posterior  belly  of  the  digastric  and  the  stylo-hyoid, 
and  enters  the  digastric  triangle,  where  it  disappears  medial 
to  the  mylo-hyoid,  and  at  the  anterior  border  of  the  hyoglossus 
it  enters  the  base  of  the  tongue. 

Branches  of  Comnnmication. — Near  the  base  of  the  skull  the  hypoglossal 
is  brought  into  connection  with — (i)  the  superior  cervical  ganglion  ;  (2)  the 
vagus  ;  and  (3)  the  first  cervical  nerve  ;  as  it  turns  round  the  occipital 
artery  it  receives  (4)  the  ramus  lingualis  vagi  from  the  pharyngeal  plexus  ; 
and  on  the  surface  of  the  hyoglossus  it  communicates  with  (5)  the  lingual 
nerve  (p.  290). 

Branches  of  Distributio?i. — (i)  The  meningeal  bi'ancJi  arises 
in  the  upper  part  of  the  canalis  hypoglossi,  and,  regaining  the 
interior  of  the  cranium,  it  is  distributed  to  the  dura  mater 
around  the  foramen  magnum.  (2)  Vascular  twigs  are  said  to 
be  supplied  to  the  deep  aspect  of  the  internal  jugular  vein. 
(3)  The  descendens  hypoglossi^  which  conveys  fibres  of  the 
first  cervical  nerve  to  the  infra-hyoid  muscles.  (4)  The  nerve 
to  the  thyreo-hyoid,  which  also  consists  of  first  cervical  nerve 
fibres.  (5)  The  terminal  branches,  which  supply  the  genio- 
hyoid and  all  the  intrinsic  and  extrinsic  muscles  of  the  tongue, 
except  the  palato-glossus. 


GREAT  VESSELS  AND  NERVES  OF  NECK    317 

Dissection. — In  the  dissection  of  the  neck  the  greater  part  of  the  cervical 
sympathetic,  with  the  branches  which  proceed  from  it,  has  been  displayed. 
The  inferior  ganglion,  which  lies  deeply  in  the  hollow  between  the 
transverse  process  of  the  seventh  cervical  vertebra  and  the  neck  of  the  first 
rib,  is  still  to  a  certain  extent  concealed,  and  must  now  be  displayed. 
Dislodge  the  subclavian  artery  from  its  place  on  the  first  rib  behind  the 
scalenus  anterior  muscle,  and  turn  it  medially.  To  do  this  efficiently, 
it  will  be  necessary  to  cut  the  costo-cervical  artery  at  its  origin.  Great  care 
must  be  taken  to  preserve  uninjured  the  fine  nerves  which  proceed  down- 
wards anterior  to  the  first  part  of  the  subclavian  artery.  If  more  space  for 
the  dissection  is  required,  the  anterior  part  of  the  first  rib  may  be  removed 
by  the  bone-forceps,  but,  as  a  general  rule,  this  will  not  be  necessary. 

Truncus  Sympathicus  in  the  Neck. — The  cervical  part  of 
the  sympathetic  trunk  takes  a  vertical  course  through  the  neck, 
anterior  to  the  roots  of  the  transverse  processes  of  the  vertebrae. 
It  Hes  between  the  internal  and  common  carotid  arteries 
anteriorly  and  the  longus  capitis  (O.T.  rectus  capitis  anticus 
major)  and  longus  colli  muscles  posteriorly.  Above.,  it  is  pro- 
longed upwards  in  the  form  of  a  stout,  ascending  nerve-trunk, 
the  nervus  caroticus  internus,  which  accompanies  the  internal 
carotid  artery  into  the  carotid  canal ;  below,  it  becomes  con- 
tinuous, over  the  neck  of  the  first  rib  and  posterior  to  the 
apex  of  the  pleura,  with  the  thoracic  portion  of  the  sympa- 
thetic. Only  three  ganglia  are  developed  upon  this  part  of 
the  trunk  and  no  white  rami  communicantes  from  the  cervical 
nerves  enter  either  the  trunk  or  the  ganglia. 

Ganglion  Cervicale  Superius. — This,  the  largest  of  the 
three  ganglia,  is  an  elongated  fusiform  body  which  varies 
somewhat  in  size.  It  is  placed  upon  the  upper  part  of  the 
longus  capitis,  opposite  the  second  and  third  vertebrae,  and 
posterior  to  the  carotid  sheath.  From  its  upper  end  the  stout 
nervus  caroticus  internus  passes  into  the  carotid  canal,  whilst 
its  lower  end  tapers  into  the  downward  continuation  of  the 
trunk.  Numerous  branches  issue  from  it ;  of  these  some 
connect  it  with  neighbouring  nerves,  whilst  others  are 
distributed  in  various  ways. 

The  connecting  branches  are:  (i)  slender  grey  rami 
com?fumica?ites  which  connect  it  with  the  upper  four  cervical 
nerves  ;  (2)  twigs  to  both  ganglia  of  the  vagus ;  (3)  to  the 
petrous  ganglion  of  the  glosso  -  pharyngeal ;  and  (4)  to  the 
hypoglossal.      It  is  not  connected  with  the  accessory. 

The  branches  of  distribution  are:  (i)  nervus  caroticus 
internus;  (2)  nervi  carotici  externi ;  (3)  rami  laryngo- 
pharyngei ;  (4)  nervus  cardiacus  superior. 


3i8  HEAD  AND  NECK 

Nervus  Caroticus  Infernus. — This  branch  has  been  noted 
passing  from  the  upper  end  of  the  ganglion  into  the  carotid 
canal.      Its  distribution  will  be  considered  later. 

Nervi  Carotid  Externi. — Two  to  six  filaments,  called 
external  carotid  branches,  run  to  the  external  carotid  artery, 
and  form  a  loose  interlacement  around  it  and  its  branches. 
From  this  external  carotid  plexus  a  branch  is  given  to  the 
carotid  body,  and  prolongations  are  continued  on  all  the 
branches  of  the  artery.  The  part  continued  upon  the  external 
maxillary  artery  supplies  the  sympathetic  root  to  the  sub- 
maxillary ganglion,  whilst  the  subdivision  upon  the  middle 
meningeal  artery  furnishes  the  corresponding  root  to  the  otic 
ganglion,  as  well  as  the  external  superficial  petrosal  nerve  which 
runs  to  the  ganglion  geniculi  of  the  facial  nerve. 

Rami  Lary?igopharyngei. — The  laryngo-pharyngeal  branches 
pass  between  the  two  carotid  arteries  to  join  the  pharyngeal 
plexus,  and  some  join  the  superior  laryngeal  nerve. 

Nervus  Cardiacus  Superior. — This  is  a  long  slender  branch 
which  springs  by  several  roots  from  the  ganglion,  and  then 
proceeds  downwards,  posterior  to  the  carotid  artery.  At 
different  stages  of  its  course  it  is  joined  by  other  branches  of 
the  sympathetic,  by  a  branch  from  the  vagus,  and  also  by 
filaments  from  the  external  laryngeal  and  recurrent  nerves. 
The  right  superior  cardiac  nerve  is  continued  into  the  thorax 
by  passing  posterior  or  anterior  to  the  subclavian  artery,  and  it 
ends  in  the  deep  cardiac  plexus.  The  left  superior  cardiac  nerve 
follows  the  left  common  carotid  artery  in  the  thorax,  and, 
crossing  the  left  side  of  the  arch  of  the  aorta,  ends  in  the 
superficial  cardiac  plexus. 

Ganglion  Cervicale  Medium.  —  This  ganglion  is  the 
smallest  of  the  three  ganglia  of  the  neck.  It  is  placed 
opposite  the  sixth  cervical  vertebra  in  close  proximity  to 
the  inferior  thyreoid  artery,  upon  which  it  not  infrequently 
rests.  Its  branches  are:  {\)  grey  rami  communicantes^  which 
pass  between  the  contiguous  margins  of  the  scalenus  anterior 
and  longus  colli  muscles  and  connect  it  with  the  fifth  and 
sixth  cervical  nerves)  (2)  thyreoid  branches^  which  run  to  the 
thyreoid  gland,  along  the  inferior  thyreoid  artery,  and  form 
connections  with  the  external  laryngeal  and  recurrent  nerves ; 
(3)  the  middle  cardiac  nerve. 

On  both  sides  the  middle  cardiac  nerve  enters  the  thorax 
and  is  lost  in  the    deep  cardiac  plexus.     On  the  right  side 


THYREOID  GLAND  319 

it  passes  posterior  or  anterior  to  the  subclavian  artery ;  on 
the  left  side  it  is  continued  downwards  between  the  common 
carotid  and  subclavian  arteries. 

Ganglion  Cervicale  Inferius. — The  inferior  cervical  ganglion 
is  lodged  in  the  interval  between  the  transverse  process  of  the 
seventh  cervical  vertebra  and  the  neck  of  the  first  rib.  In  this 
position  it  lies  posterior  to  the  vertebral  artery.  It  is  by  no 
means  uncommon  to  find  it  more  or  less  completely  fused, 
over  the  neck  of  the  first  rib,  with  the  first  thoracic  ganglion. 
The  connection  between  it  and  the  middle  cervical  ganglion  is 
generally  in  the  form  of  two  or  more  slender  nerve  cords,  of 
which  one  passes  anterior  to  the  subclavian  artery.  The 
latter  loops  round  the  subclavian  artery  and  is  termed  the 
ansa  subclavia  (Vieussenii). 

The  branches  of  the  inferior  cervical  ganglion  are  : — 

1.  Grey  rami  communicantes  to  the  seventh  and  eighth  cervical  nerves. 

2.  Rami  vasculares. 

3.  Inferior  cardiac  nerve. 

The  rami  vasculares  are  fine  branches  which  form  a  plexus 
around  the  subclavian  artery  and  its  branches.  Those 
around  the  vertebral  artery  are  remarkable  for  their  large  size. 

The  ?iervus  cardiacus  inferior  on  both  sides  enters  the  deep 
cardiac  plexus. 

After  the  vessels  and  nerves  of  the  neck  have  been  studied 
the  dissectors  should  examine  the  thyreoid  gland. 

Glandula  Thyreoidea. — The  thyreoid  gland  is  a  highly 
vascular  solid  body,  which  clas$)s  the  upper  part  of  the 
trachea  and  extends  upwards  for  some  distance  upon  each 
side  of  the  larynx.  It  varies  greatly  in  size  in  different  in- 
dividuals ;  and  in  females  and  children  it  is  always  relatively 
larger  than  in  adult  males.  It  consists  of  three  well-marked 
subdivisions,  viz.,  two  lateral  lobes  joined  across  the  median 
plane  by  the  isthmus.  Each  lateral  lobe  is  somewhat  conical 
in  form ;  its  base  lies  at  the  level  of  the  fifth  or  the  sixth 
tracheal  ring,  whilst  its  apex  rests  against  the  side  of  the 
thyreoid  cartilage.  Its  superficial  or  lateral  surface  is  full  and 
rounded,  and  is  clothed  by  the  pretracheal  layer  of  cervical 
fascia,  from  which  it  derives  a  sheath  ;  and  it  is  covered  by  the 
sterno-thyreoid,  sterno-hyoid,  and  omo-hyoid  muscles,  and  by 
the  anterior  border  of  the  sterno-mastoid  (Fig.  127,  p.  322). 
Its  deep  or  7nedial  surface  is  adapted  to  the  parts  upon  which  it 


320 


HEAD  AND  NECK 


lies,  viz.,  to  the  side  of  the  trachea,  the  cricoid  cartilage, 
and  the  thyreoid  cartilage.  Its  posterior  border  is  in  relation 
with  the  lateral  margins  of  the  oesophagus  and  the  lateral 
margin  of  the  pharynx,  and  in  many  cases  it  overlaps  the 
common  carotid  artery.     Its  anterior  border  is  connected  with 


Anterior  facial  vein 
Mylo-hyoid 
muscle"" 
Common  facial 
vein- 
Lingual  vein... 
Small  occipital  N., 
Great  auricular  N.- 
Nervus 
cutaneus  colli"" 
Internal  jugular  vein* 
Descending 
cervical" 

nerves 
Brachial.' 

plexus 
External, 
jugular  vein 
Descendens 
hypoglossi 
Anterioi 
jugular  vein 

Inferioi 
thyreoid  veins'  " 


Platysma 


External  maxillary 
artery 

Parotid  gland 
Submental  lymph 
gland 
Submaxillary  gland 

Sterno-mastoid  artery 
Ext.  carotid  artery 

Sup.  thyreoid  artery 
Common  carotid 
artery 
Lymph  gland 

Thyreo-glossal  duct 
Omo-hyoid 

Crico-thyreoid 


Sterno-hyoid 

Isthmus  of  thyreoid 
j:land 


Sterno- thyreoid 


Fig.  126, — Dissection  of  the  Anterior  Part  of  the  Neck, 
mastoid  has  been  removed. 


The  Right  Sterno- 


the  corresponding  border  of  the  opposite  lateral  lobe  by  the 
isthmus.  Above  the  isthmus  it  is  in  relation  with  the  anterior 
terminal  branch  of  the  superior  thyreoid  artery,  and  below  the 
isthmus  with  the  commencement  of  the  inferior  thyreoid  vein. 
The  isthmus  of  the  thyreoid  gland  has  already  been  seen 
in  the  dissection  of  the  middle  line  of  the  neck.  It  is  a 
band  of  varying  width  which  lies  anterior  to  the  second,  third, 


TRACHEA  AND  CESOPHAGUS  321 

and   fourth  rings  of  the  trachea,   and,   therefore,  nearer  the 
lower  than  the  upper  ends  of  the  two  lateral  lobes. 

An  additional  lobe,  the  pyra??iidal  or  viiddle  lobe,  is 
frequently  present.  It  is  an  elongated  slender  process  which 
springs  frorri  the  isthmus,  on  one  or  other  side  of  the  median 
plane  (more  usually  on  the  left  side),  and  extends  upwards 
towards  the  hyoid  bone.  To  this  it  may  be  connected  by 
fibrous  tissue,  or  by  a  narrow  slip  of  muscular  fibres  called 
the  levator  glandulce  thyreoidece.  In  some  cases  this  little 
muscle  has  an  attachment  to  the  thyreoid  gland  independ- 
ently of  the  pyramidal  process.  The  thyreoid  gland  is  firmly 
connected  to  the  parts  upon  which  it  Hes,  and  therefore 
follows  the  larynx  in  all  its  movements. 

The  dissector  should  note  the  great  vascularity  of  the  thyreoid  gland. 
Four  large  arteries,  and  occasionally  a  fifth  smaller  vessel,  convey  blood  to 
its  substance.  The  two  superior  thyreoid  branches  of  the  external  carotid 
arteries  divide  at  the  apex  of  each  lateral  lobe  into  three  branches  for  its 
supply  ;  the  two  inferior  thyreoid  branches,  from  the  thyreo-cervical  trunks 
of  the  subclavian  arteries,  distribute  their  terminal  branches  to  the  basal 
portion  and  deep  surface  of  each  lateral  lobe.  The  occasional  artery  is 
the  thyreoidea  inia,  a  branch  of  the  innominate  or,  more  rarely,  of  the 
common  carotid  or  the  aortic  arch.  It  ascends  upon  the  anterior  aspect 
of  the  trachea  to  reach  the  isthmus  of  the  thyreoid  gland.  These  thyreoid 
arteries  anastomose  with  each  other. 

The  veins  which  drain  the  blood  away  from  the  thyreoid  gland  are  still 
more  numerous.  They  arise  in  part  by  tributaries  which  spring  from  a 
venous  network  on  the  anterior  face  of  the  structure,  but  chiefly  by  branches 
which  emerge  from  its  substance.  They  are  three  in  number  on  each  side 
— viz.  the  superior  thyreoid,  the  middle  thyreoid,  and  the  inferior  thyreoid. 
The  superior  and  middle  thyi'coid  veins  cxos%  the  common  carotid  artery  and 
join  the  internal  jugular  ;  the  infej-ior  thyreoid  vein  descends  on  the  trachea. 
At  the  root  of  the  neck  it  usually  joins  its  fellow  of  the  opposite  side  to 
form  a  common  stem  which  opens  into  the  left  innominate. 

Trachea  and  (Esophagus. — The  windpipe  and  the  gullet 
in  the  cervical  portion  of  their  course  may  now  be  studied. 
Both  begin  at  the  level  of  the  cricoid  cartilage,  anterior  to 
the  sixth  cervical  vertebra.  From  this  point  they  extend 
downwards,  anterior  to  the  vertebral  column,  to  the  thoracic 
cavity. 

The  trachea,  or  wijidpipe,  is  a  wide  tube  which  is  kept 
constantly  patent  by  the  cartilaginous  rings  embedded  in  its 
walls.  These  rings  do  not  form  complete  circles  ;  posteriorly 
they  are  deficient,  and,  in  consequence,  the  posterior  surface 
of  the  trachea  is  flattened.  Above,  it  is  continuous  with  the 
larynx,  and,  throughout  its  course  in  the  neck,  it  is  placed  in 
the  median  plane  of  the  body.      The  ajiterior  relations  of  the 

VOL.  II — 21 


322 


HEAD  AND  NECK 


trachea  have  already  been  fully  discussed  in  connection  with 
the  description  of  the  parts  occupying  the  middle  line  of  the 
neck  (p.  229).  Posteriorly^  it  rests  upon  the  gullet.  Upon 
either  side  is  the  common  carotid  artery ;  whilst  closely  applied 
to  it  in  its  upper  part  is  the  lateral  lobe  of  the  thyreoid 
gland.  The  recurrent  nerve  ascends,  on  each  side,  in  the 
angle  between  the  trachea  and  oesophagus. 

The  oesophagus  or  gullet  is  a  narrow  tube,  with  thick 
muscular  walls,  which  extends  from  the  pharynx  to  the 
stomach.  In  the  cervical  part  of  its  course  it  lies  between  the 
trachea   and    the  longus   colli   muscles,    and   as  it  descends 


Trachea 


Recurrent  nerve 


Common  carotid  artery 
Internal  jugular  vein 


Thyreoid  gland 

Sterno-thj'reoid 

Sterno-hyold 

/---  Sterno-mastoid 


~~    Recurrent  nerve 
Vertebral  vein 


Vagus  nerve 

^^/^ 
Inferior  thyreoid  artery 

Vertebral  vein  /       '     '   I  , .  ,  \  '  - 

/  /    '  '  '  i 

Vertebral  artery  /     CEsophagus  ist  dorsal  vertebra 

Longus  colli 

Fig.   127. — Transverse  section  through  the  Thyreoid  Glaad,  Trachea,  and 
Gullet,  at  the  level  of  the  first  Thoracic  Vertebra. 

it  inclines  slightly  to  the  left,  so  that  it  comes  more  closely 
into  relation  with  the  lateral  lobe  of  the  thyreoid  gland  and 
the  carotid  sheath  upon  the  left  side  than  with  the  same 
structures  on  the  opposite  side. 

The  dissector  may  terminate  his  dissection  of  the  neck  by 
an  examination  of  the  scalene  muscles,  and  the  rectus  capitis 
lateralis. 

Musculi  Scaleni. — These  muscles  constitute  the  fleshy  mass 
which  is  seen  extending  from  the  transverse  processes  of  the 
cervical  vertebrae  to  the  upper  two  costal  arches.  They  are 
three  in  number,  and  are  named,  from  their  relative  positions, 
anterior,  medius,  zxi^  posterior. 

Musculus  Scalenus  Anterior. — This  is  a  well-defined  muscle 
which  is  separated  from  the  scalenus  medius  by  the  roots  of 


SCALENE  MUSCLES  323 

the  brachial  plexus  and  the  subclavian  artery.  It  arises  from 
the  anterior  tubercles  of  the  transverse  processes  of  the  third, 
fourth,  fifth,  and  sixth  cervical  vertebrae,  and,  tapering  some- 
what as  it  descends,  it  is  inserted  into  the  scalene  tubercle 
on  the  inner  margin  of  the  first  rib,  and  also  into  the 
superior  surface  of  the  same  bone  between  the  two  subclavian 
grooves. 

The  upper  part  of  its  anterior  surface  is  concealed  by  the 
sterno- mastoid  and  the  lower  part  by  the  clavicle.  The 
common  carotid  artery  descends  along  its  medial  border. 
Between  it  and  the  sterno-mastoid  lie  the  internal  jugular 
vein  j  the  intermediate  tendon  of  the  omo-hyoid  ;  the  phrenic 
nerve,  passing  downwards  and  medially ;  and  the  transverse 
cervical  and  transverse  scapular  arteries  passing  postero- 
laterally,  superficial  to  the  phrenic  nerve.  Between  it  and 
the  clavicle  lies  the  subclavian  vein. 

Its  posterior  surface  is  in  relation,  above,  with  the  tips  of 
the  lower  cervical  transverse  processes,  and  below,  with  the 
apex  of  the  pleura,  the  second  part  of  the  subclavian  artery, 
and  its  costo-cervical  branch.  The  lateral  border  touches  the 
roots  of  the  brachial  plexus,  and  the  medial  border  is  in 
relation  with  the  thyreo-cervical  artery,  its  inferior  thyreoid 
branch,  and  with  the  vertebral  artery. 

Musculus  Scalenus  Medius. — This  is  a  more  powerful 
muscle  than  the  preceding.  It  springs  from  the  posterior 
tubercles  of  all  the  cervical  transverse  processes  (with  the 
exception,  in  some  cases,  of  the  first),  and  it  is  inserted  into 
a  rough  oval  impression  which  marks  the  upper  surface  of 
the  first  rib  between  the  tubercle  of  the  rib  and  the  groove 
for  the  subclavian  artery. 

It  forms  part  of  the  floor  of  the  posterior  triangle  of  the 
neck.  Its  superficial  surface  is  in  relation  with  the  brachial 
plexus  and  the  third  part  of  the  subclavian  artery.  Its 
posterior  border  touches  the  levator  scapulae ;  and  the  dorsal 
scapular  nerve  and  the  descending  branch  of  the  transverse 
cervical  artery  pass  between  it  and  that  muscle.  The  lower 
part  of  its  anterior  border  is  in  relation  with  the  apex  of 
the  pleura,  and  the  upper  two  roots  of  the  long  thoracic 
nerve  pierce  the  substance  of  the  muscle. 

Musculus  Scalenus  Posterior.  —  The  scalenus  posterior  is 
generally  inseparable,  at  its  origin,  from  the  scalenus  medius. 
It  is  the  smallest  of  the  three,  and  springs  by  two  or  three 

II— 21a 


324 


HEAD  AND  NECK 


slips  from  the  transverse  processes  of  a  corresponding  number 
of  the  lower  cervical  vertebrae  in  common  with  the  scalenus 
medius.  It  is  inserted  into  the  upper  border  of  the  second 
rib,  immediately  anterior  to  the  insertion  of  the  levator 
costae. 

The  scalene  muscles  are  supplied  by  twigs  from  the 
anterior  branches  of  the  cervical  nerves^  particularly  the  lower 
four. 


Serratus  posterior 
superior  (insertion) 


Scalenus  posterior 
(insertion) 


Scalenus  medius  (insertion) 


Serratus  anterior  (origin) 


Serratus  anterior 

(origin)      '\!l|||\  A 


Scalenus  anterior  (insertion) 


Subclavius 
(origin) 


Pectoralis  minor  (occasional  origin) 


Fig.  128. — Muscle-Attachments  to  the  Superior  Surface  of  the 

First  Rib,  and  the  Outer  Surface  of  the  Second  Rib. 

A,  First  rib  ;  B,  Second  rib. 


Dissection.— ThQ  little  muscle  termed  the  rectus  capitis  lateralis  should 
now  be  cleaned,  and  its  attachments  defined.  It  lies  in  the  interval 
between  the  transverse  process  of  the  atlas  and  the  jugular  process  of  the 
occipital  bone,  posterior  to  the  commencement  of  the  internal  jugular 
vein.  The  anterior  branch  of  the  first  cervical  nerve  will  be  seen  emerging 
from  under  cover  of  its  medial  margin. 


LATERAL  PART  OF  MIDDLE  CRANIAL  FOSSA    325 

Rectus  Capitis  Lateralis. — The  rectus  lateralis  arises  from 
the  anterior  part  of  the  upper  surface  of  the  extremity  of  the 
transverse  process  of  the  atlas,  and  is  inserted  into  the  under 
surface  of  the  jugular  process  of  the  occipital  bone.  It  is 
supplied  by  a  twig  from  the  anterior  branch  of  the  first 
cervical  nerve. 

Removal  of  the  Head  and  Neck  from  the  Trunk. — By  the  time  that 
the  dissectors  of  the  head  and  neck  have  arrived  at  this  stage  of  their  work, 
the  dissectors  of  the  thorax  have  in  all  probability  finished  their  dissection. 
If  this  is  the  case,  the  head  and  neck  may  be  removed  from  the  trunk  by 
cutting  through  the  vertebral  column  at  the  level  of  the  intervertebral  fibro- 
cartilage  between  the  third  and  fourth  thoracic  vertebrae.  By  this  pro- 
ceeding the  upper  three  thoracic  vertebrae,  with  the  attached  portions  of  the 
first,  second,  and  third  pairs  of  ribs,  are  removed  with  the  neck.  The 
scalene  muscles  and  the  longus  colli  are  therefore  preserved  intact. 


THE  LATERAL  PART  OF  THE  MIDDLE 
CRANIAL  FOSSA. 

The  structures  contained  within  the  middle  cranial  fossa 
may  now  be  examined.  In  carrying  out  this  dissection,  the 
head  should  be  supported  on  a  block  so  that  the  floor  of 
the  cranial  cavity  looks  upw^ards.  The  following  are  the 
structures  which  must  be  displayed  : — 

1.  Cavernous  venous  sinus. 

2.  Internal  carotid  artery-. 

3.  Middle  meningeal  artery. 

4.  Accessory  meningeal  artery. 

5.  The   two   roots  of  the  Trigeminal  nerve,    with  the   Semilimar 

ganglion    and    the    three    main    divisions    of    the    trigeminal 
nerve. 

6.  Oculo-motor  nerve  (3rd  cerebral). 

7.  Trochlear  nerve  (4th  cerebral). 

8.  Abducent  nerve  (6th  cerebral). 

9.  Internal  carotid  plexus  of  the  sympathetic. 

10.  Greater  superficial  petrosal  nerve. 

11.  Smaller  superficial  petrosal  nerve. 

Dissection. — The  dura  mater  has  already  been  removed  from  one  half  of 
the  middle  cranial  fossa,  and  on  that  side  it  is  only  necessary  to  differentiate 
the  structures  which  lie  in  the  cavernous  sinus  ;  on  the  other  side  the  dura 
mater  must  be  stripped  from  the  medial  part  of  the  lateral  portion  of  the 
middle  cranial  fossa.  Enter  the  knife  at  the  anterior  clinoid  process,  and 
carry  it  posteriorly  to  the  apex  of  the  petrous  bone.  This  incision  must  go 
no  deeper  than  is  necessary  to  divide  the  dura  mater,  and  must  be  made 
immediately  to  the  lateral  side  of  the  openings  in  the  membrane  through 
which  the  oculo-motor,  the  trochlear,  and  trigeminal  nerves  pass.      It   is 


326 


HEAD  AND  NECK 


very  important  to  preserve  these  apertures  intact,  so  that  the  proximal 
ends  of  the  nerves  may  be  held  in  position  during  the  dissection.  The 
incision  through  the  dura  mater  may  now  be  carried  postero-laterally  along 
the  upper  border  of  the  petrous  bone  in  the  line  of  the  superior  petrosal 
sinus,  and  antero-laterally  along  the  posterior  margin  of  the  lesser  wing  of 
the  sphenoid.  After  the  incisions  are  made  raise  the  dura  mater  with  great 
care,  for  it  is  intimately  connected  with  the  nerves  which  lie  subjacent  to 
it.  Thus,  where  it  forms  the  lateral  wall  of  the  cavernous  sinus,  it 
is  closely  applied  to  the  oculo- motor  and  trochlear  nerves,  and  firmly 
attached  to  the  ophthalmic  division  of  the  trigeminal  nerve,  whilst  over 
the  petrous  bone  it  is  united  to  the  surface  of  the  semilunar  ganglion. 
The  edge  of  the  knife,  therefore,  must  be  kept  close  to  the  membrane,  and 
a  small  portion  of  the  membrane  may  be  left  upon  the  nerves.  This  can 
be  removed  afterwards  as  the  nerves  are  defined. 

Sinus  Cavernosus. — The  cavernous  sinus  has  been  opened 


,NT    CAROTID       INTUNDIBULU 


0  C  ULO-MOT 
TR  O  C  H  LE  A 


M. 


Fig.  129. — Section  through  the  Cavernous  Sinus.      (After 
Merkel,  somewhat  modified. ) 


by  the  above  dissection.      It  is  a  short,  wide  venous  channel, 

which  extends  along  the  side  of  the  body  of  the  sphenoid  bone, 

from  the  lower  and  medial  end  of  the  superior  orbital  fissure 

(O.T.  sphenoidal  fissure)  to  the  apex  of  the  petrous  portion 

of  the  temporal  bone.     Anteriorly,  blood  is  conducted  into  it 

by  the  ophthalmic  veins  and  the  spheno-parietal  sinus ;  whilst 

posteriorly  the  blood  is  drained  away  by  the   superior   and 

inferior  petrosal  sinuses.      But  it  has  still  other  connections. 

Thus,   it  receives  blood  from  the  lower  part   of  the  lateral 

surface  of  the  brain  by  the  superficial  middle  cerebral  vein 

and   some   small   inferior   cerebral  veins.     It  is  united  with 

the  corresponding  sinus  of  the  opposite  side  by  means  of  the 

anterior  and  posterior  intercavernous  sinuses  (p.  217).    Lastly, 

one  or  more  emissary  veins  leave  its  lower  aspect ;  one  passes 

out   of   the   cranium   by  the    foramen   ovale,   or    it   may   be 


LATERAL  PART  OF  MIDDLE  CRANIAL  FOSSA   327 


through  the  foramen  VesaHi,  to  the  pterygoid  venous  plexus ; 
and  others  accompany  the  internal  carotid  artery,  through 
the  foramen  lacerum  and  the  carotid  canal,  and  end  in  the 
pharyngeal  plexus. 

The  cavernous  sinus  is  formed  in  the  same  manner  as 
the  other  venous  sinuses.  The  two  layers  of  the  dura  mater 
are  separated  from  each  other,  and  the  interval  is  lined  with 
a  delicate  membrane.  A  comphcated  network  of  interlacing 
trabeculae  occupies  the  lumen  of  the  channel,  and  it  is  on 
this   account   that   the   term    "  cavernous "   is   apphed   to  it. 


Oculo-motor  nerve 

Trochlear  nerve 

Ophthalmic 
ner^e 
Abducent 
nerve 

Maxillary 
ners'e 


Infundibulum 
Hypophysis  \ 


Optic  nerve 

Internal  carotid  artery 

Oculo-motor  nerve 


Trochlear 
nerve 

Ophthalmic 

nerve 

Int.  carotid 

artery 

Aljducent 

nerve 

Maxillary 

nerve 


Pterygoid  fossa 


Choanae 


Vomer 


Fig.  130. — Frontal  section  through  the  Cavernous  Sinus  to  show  the  position 
of  the  Nerves  in  its  wall.  Note  the  branch  given  to  the  hypophysis 
(O.T.  pituitary  body)  by  the  internal  carotid  artery. 

This  sinus  has  a  special  importance  on  account  of  its  being 
traversed  by  the  internal  carotid  artery ;  the  internal  carotid 
plexus;  the  oculo-motor,  trochlear,  and  abducent  nerves; 
and  the  ophthalmic  division  of  the  trigeminal  nerve.  The 
precise  relations  which  these  structures  bear  to  its  walls  will 
be  described  later ;  in  the  meantime  it  is  necessary  only 
to  note  that  two,  viz.  the  internal  carotid  artery  and  the 
abducent  nerve,  lie  more  distinctly  within  the  interval  between 
the  two  layers  of  the  dura  mater  than  the  others,  but  that 
they  are  shut  out  from  the  blood  channel  by  the  delicate 
lining  membrane  of  the  sinus.  The  oculo-motor  and  trochlear 
nerves,  and  the  ophthalmic  division  of  the  trigeminal  nerve, 
are  closely  applied  to  the  lateral  wall  of  the  sinus. 
I  [—21  h 


328 


HEAD  AND  NECK 


Nervus  Trigeminus. — The  two  roots  of  this  nerve  have 
already  been  seen  piercing  the  dura  mater  at  the  apex  of 
the  petrous  portion  of  the  temporal  bone  under  the  anterior 
margin  of  the  tentorium.  Now  that  the  dura  mater  has  been 
raised  from  the  lateral  part  of  the  middle  cranial  fossa,  the 
further  relations  of  these  nerve-roots  within  the  cranium  may 
be  studied!     It  will   be  noticed  that   the  loosely  connected 


Levator  palpebrse  superioris 

Superior  rectus  —  — 


Superior  oblique 
Lacrimal  gland 


Lateral  rectus 


Sixth  nerve 


Ciliary  ganglion 
Naso-ciliary  nerve 

Ophthalmic  division 

of  fifth  nerve    i — ~~\m 


Maxillary  division 
of  fifth  nerve 

Motor  root  of 
fifth  nerve 


Trochlea 


'-J—  Superior  oblique 


Inferior  rectus 
Medial  rectus 

^5 !  7 Fourth  nerve 

Sixth  nerve 


Optic  nerve 


Semilunar  ganglion 
Mandibular  division  of  fifth  nerve 


Third  nerve 


Sixth  nerve 
Fourth  nerve 


Fig.  131.— Dissection  of  the  Orbit  and  the  Middle  Cranial  Fossa.     Both 
roots  of  the  fifth  nerve  with  the  semilunar  ganglion  are  turned  laterally. 

and  parallel  funiculi  of  the  portio  major,  or  sensory  root,  at 
once  begin  to  divide  and  join  with  each  other  so  as  to 
form  a  dense  plexiform  arrangement,  whilst,  at  the  same  time, 
the  nerve-root  increases  somewhat  in  breadth.  The  interlace- 
ment, thus  brought  about,  occupies  the  smooth  depression 
which  marks  the  anterior  aspect  of  the  apex  of  the  petrous 
portion  of  the  temporal  bone,  and  it  sinks  into  the  semilunar 
ganglion  (O.T.  Gasserian). 


LATERAL  PART  OF  MIDDLE  CRANIAL  FOSSA    329 

The  Ganglion  Semilunare  (O.T.  Gasserian)  is  somewhat 
crescentic  in  form.  It  lies  upon  the  sutural  junction  between 
the  apex  of  the  petrous  bone  and  the  great  wing  of  the 
sphenoid  bone,  where  it  is  enclosed  within  a  recess  or  space, 
called  the  cavu?n  Meckelii^  formed  by  a  separation  of  the  two 
layers  of  the  dura  mater.  The  concavity  of  the  ganglion  is 
directed  postero-medially,  and  it  is  upon  this  aspect  that  it 
receives  the  interlacing  fibres  of  the  sensory  root  of  the 
trigeminal  nerve ;  the  convexity  of  the  ganglion  is  directed 
antero-laterally  and  from  it  emerge  the  three  main  divisions 
of  the  trigeminal  nerve.  These  are — (i)  the  first,  or 
ophthalmic  division  ;  (2)  the  second,  or  maxillary  division  ; 
and  (3)  the  third,  or  mandibular  division.  The  medial 
border  of  the  ganglion  is  connected  with  the  internal 
carotid  sympathetic  plexus  by  filaments  of  communication. 

The  portio  minor  or  motor  root  of  the  fifth  nerve  should  now 
be  followed.  Before  the  nerve  pierces  the  dura  mater  the 
motor  root  lies  along  the  medial  side  of  the  large  sensory  root, 
but  it  soon  changes  its  position  and  comes  to  lie  beneath 
the  sensory  part.  To  display  this  relationship,  draw  the 
cut  ends  of  the  two  roots  through  the  aperture  in  the  dura 
mater  which  leads  into  the  cavum  Meckelii,  and,  gently 
dislodging  the  semilunar  ganglion  from  its  place,  turn  it 
antero-laterally  so  as  to  expose  its  deep  surface.  The  small 
and  firm  motor  root  can  readily  be  recognised  lying  in  a 
groove  upon  the  deep  surface  of  the  ganglion ;  and  if  it  is 
displaced  from  this,  it  will  be  seen  to  have  no  connection  with 
the  ganglion,  but  to  be  continued  onwards  towards  the  foramen 
ovale.  It  ultimately  joins  the  mandibular  division  of  the 
trigeminal  nerve.  This  junction  may  take  place  within  the 
cranium,  in  the  foramen  ovale,  or  immediately  outside  the 
skull. 

The  three  principal  divisions  of  the  trigeminal  nerve  may 
next  be  examined.  Begin  with  the  fnandibular  division^ 
which  is  the  largest.  This  proceeds  directly  downwards,  and 
almost  immediately  leaves  the  cranial  cavity  through  the 
foramen  ovale. 

W..  Whilst  isolating  this  large  nerve -trunk  and  defining  the  bony  aperture 
through  which  it  makes  its  exit,  look  carefully  for  the  accessory  meningeal 
artery,  which  enters  the  cranium  through  the  same  foramen.  If  the 
injection  has  been  forced  into  this  vessel  it  can  easily  be  detected.  An 
emissary  vein  which  connects  the  cavernous  sinus  with  the  pterygoid 
venous  plexus  also  passes  through  the  foramen  ovale. 


330  HEAD  AND  NECK 

The  ?naxillary  division  is  composed  entirely  of  sensory 
fibres.  It  runs  anteriorly  in  relation  to  the  lower  and  lateral 
part  of  the  cavernous  sinus,  and,  after  a  short  course  within 
the  cranium,  makes  its  exit  through  the  foramen  rotundum. 
Near  its  origin  it  gives  off  a  fine  meningeal  branch  to  the  dura 
mater  of  the  middle  fossa  of  the  cranium. 

The  ophthalmic  division  is  the  smallest  of  the  three  branches 
of  the  trigeminal  nerve,  and,  like  the  maxillary,  it  is  com- 
posed entirely  of  sensory  fibres.  It  passes  anteriorly  in  the 
lateral  wall  of  the  cavernous  sinus,  and  ends,  close  to  the 
superior  orbital  fissure,  by  dividing  into  three  terminal  branches. 
As  it  traverses  the  sinus  it  is  accompanied  by  the  oculo- 
motor and  trochlear  nerves,  both  of  which  occupy  a  higher 
level.  Like  the  other  two  divisions  of  the  trigeminal  nerve, 
the  ophthalmic  nerve  gives  off  a  meningeal  branch.  This 
small  twig  passes  into  the  tentorium  cerebelli. 

The  terminal  branches  of  the  ophthalmic  division  of  the 
trigeminal  nerve  are  the  naso-ciliary,  the  lacrimal,  and  the 
frontal.  The  naso-ciliary.,  as  a  rule,  takes  origin  first ;  the 
lacrimal  is  given  off  soon  after ;  and  then  the  stem  of  the 
nerve  is  continued  onwards  as  the  frontal.  These  three 
nerves  enter  the  orbit  through  the  superior  orbital  fissure. 

Nervus  Oculomotorius  (Third),  Nervus  Trochlearis  (Fourth), 
and  Nervus  Abducens  (Sixth). — It  has  been  noted  already 
that  the  oculo-7notor  nerve  pierces  the  dura  mater  within  the 
small  triangular  area,  in  the  middle  cranial  fossa,  which 
lies  immediately  anterior  to  the  crossing  of  the  attached 
and  free  margins  of  the  tentorium  (p.  210).  It  has  been  noted 
also  that  the  trochlear  (fourth)  nerve  pierces  the  dura  mater 
in  the  posterior  fossa  under  the  free  margin  of  the  tentorium. 
Both  now  proceed  anteriorly  in  the  lateral  wall  of  the  cavern- 
ous sinus.  The  oculo-motor  nerve  occupies  the  highest 
level,  then  comes  the  trochlear  nerve,  and  immediately 
below  that  the  ophthalmic  division  of  the  trigeminal  nerve. 
They  therefore  present  a  numerical  order  from  above  down- 
wards. The  abducent  nerve.,  which  pierces  the  dura  mater 
in  the  posterior  fossa,  at  the  lower  and  lateral  part  of  the 
dorsum  sellse,  curves  round  the  lateral  side  of  the  internal 
carotid  artery,  and  then  passes  anteriorly  more  directly  within 
the  cavernous  sinus  than  the  others  (Fig.  130). 

The  oculo-motor,  trochlear,  and  abducent  nerves  during 
their    course    in    the    cavernous    sinus    receive    communica- 


LATERAL  PART  OF  MIDDLE  CRANIAL  FOSSA  331 

tions  from  the  carotid  plexus  and  from  the  ophthalmic 
nerve;  and  they  all  enter  the  orbit  by  passing  through 
the  superior  orbital  fissure.  Before  doing  so,  the  oculo- 
motor nerve  divides  into  an  upper  and  a  lower  division. 
As  they  pass  through  the  superior  orbital  fissure  the  various 


Infundibulum 

Abducent  nerve      /£ 

Trigeminal  nerve 

Trochlear  nerve 

Acustic  and      /  /, 
facial  nerves  "^<|/y 

Glosso-pharyn- 
geal  nerve 

Vagus  nerve— jik. 


Hypoglossal 

nerve 

Accessory  nerve 


Section  through 

the  medulla 

oblongata 


Optic  nerve 

Internal  carotid 
artery 


Posterior 
communicating 


Oculo-motor  nerve 

Posterior  cerebral 
Superior 

cerebellar 
Tentorium 

Basilar 
artery 

1}  Vertebral 
artery 


Superior  petrosal 
sinus 


Transverse  sinus 


Transverse  sinus 


Superior  sagittal  sinus 


Fig.  132. — Floor   of  the  Cranium  after  the 
Tentorium  CerebeUi.      The  blood-vessels 
have  been  left  in  place. 


Occipital  sinus 


Straight  sinus  divided 


removal  of    the  Brain  and    the 
forming;  the  circulus  arteriosus 


This, 


nerves  undergo  a  change  in   their  relative  positions. 
however,  will  be  studied  in  the  dissection  of  the  orbit. 

Arteria  Carotis  Interna. — The  intracranial  portion  of  the 
internal  carotid  artery  may  now  be  examined.  It  lies  upon 
the  lateral  aspect  of  the  body  of  the  sphenoid,  and,  for  the 
greater  part  of  its  course,  it  traverses  the  cavernous  sinus.  It 
emerges  from  the  carotid  canal  into  the  foramen  lacerum 
at  the  apex  of  the  petrous  bone ;  then  it  passes  through  the 
upper  part  of  the  foramen  lacerum,  pierces  the  outer  layer 


332  HEAD  AND  NECK 

of  dura  mater,  and  enters  the  middle  cranial  fossa  at  the  root 
of  the  posterior  clinoid  process  ;  there  it  bends  at  right  angles, 
and  passes  anteriorly  to  the  lower  root  of  the  small  wing  of 
the  sphenoid,  where  it  turns  abruptly  upwards  and  pierces 
the  inner  layer  of  the  dura  mater,  immediately  posterior  to 
the  entrance  of  the  optic  nerve  into  the  optic  foramen,  and 
on  the  medial  side  of  the  anterior  clinoid  process.  It  was 
severed  at  this  point  during  the  removal  of  the  brain ;  but  it 
will  be  afterwards  seen  to  end  on  the  basal  aspect  of  the 
brain,  at  the  commencement  of  the  fissura  lateralis  (O.T.  Sylvian 
fissure),  by  dividing  into  the  anterior  and  middle  cerebral 
arteries.  Throughout  its  whole  course  it  is  surrounded  by 
sympathetic  filaments,  and  soon  after  its  entrance  into  the 
cranium  the  abducent  nerve  crosses  its  lateral  side. 

The  intracranial  portion  of  the  internal  carotid  artery  gives 
off  the  following  branches  : — 

1.  Branches  to  the  hypophysis,  \    These  are  minute  twigs 

2.  Branches  to  the  semilunar  ganglion,      V       which    arise    in    the 

3.  Branches  to  the  dura  mater,  j        cavernous  sinus. 

4.  Ophthalmic,  ^ 

5.  Posterior  communicating,  I   These  will  be  studied  at  a  later 

6.  Anterior  cerebral,   \  terminal     j       stage. 

7.  Middle  cerebral,     /  branches.  J 

8.  Choroidal. 

Plexus  Caroticus  Internus. — The  sympathetic  filaments 
which  form  this  plexus  can  be  satisfactorily  dissected  only  in 
a  subject  which  has  not  been  injected ;  and  even  then,  the 
dissection  is  an  exceedingly  difficult  one.  The  internal  carotid 
plexus  is  placed  in  the  cavernous  sinus  and  is  chiefly  massed 
upon  the  lower  and  medial  aspect  of  the  internal  carotid 
artery,  at  the  point  where  it  makes  its  bend  upwards.  It 
supplies  filaments  to  the  hypophysis,  to  the  third  and  fourth 
nerves,  and  to  the  ophthalmic  division  of  the  trigeminal  nerve, 
and  gives  the  sympathetic  root  to  the  ciliary  ganglion  (O.T. 
lenticular  ganglion). 

Nervus  Petrosus  Superficialis  Major. — This  small  nerve, 
along  with  a  small  arterial  twig  from  the  middle  meningeal 
artery,  can  readily  be  exposed  in  the  groove  on  the  anterior 
face  of  the  petrous  bone  which  leads  from  the  hiatus  canalis 
facialis  to  the  foramen  lacerum.  It  is  placed  under  the  semilunar 
ganglion,  which  must  therefore  be  turned  antero-laterally. 
In  the  canalis  facialis  it  joins  the  ganglion  geniculi  of  the 
facial  nerve.     When  traced  in  the  opposite  direction,  it  will 


DISSECTION  OF  THE  ORBIT  333 

be  found  to  enter  the  foramen  lacerum,  where  it  joins  the 
nerviis  petrosus  profundus  from  the  carotid  plexus.  The  trunk 
formed  by  the  union  of  these  two  filaments  is  the  ?tervus 
ca?ialis  pterygoidei  {O.T.   Vidian  nerve). 

Nervus  Petrosus  Superficialis  Minor  appears  upon  the  anterior  face 
of  the  petrous  bone,  through  an  aperture  which  is  placed  immediately 
lateral  to  the  hiatus  canalis  facialis.  It  leaves  the  cranial  cavity  by  passing 
downwards  between  the  great  wing  of  the  sphenoid  and  the  petrous  part 
of  the  temporal  bone,  or  through  the  canaliculus  innominatus  or  through 
the  foramen  ovale,  to  reach  the  otic  ganglion.  This  minute  nerve,  as 
has  been  mentioned  already  (p.  312),  is  formed  by  the  union  of  the 
tympanic  branch  of  the  glosso-pharyngeal  with  a  branch  from  the  ganglion 
geniculi  of  the  facial. 

External  Superficial  Petrosal  Nerve. — It  is  convenient  at  this  stage  to 
take  note  of  a  fourth  petrosal  nerve — the  extevfial  superficial  petrosal.  It 
takes  origin  from  the  sympathetic  plexus  which  accompanies  the  middle 
meningeal  artery,  and,  entering  the  petrous  bone,  is  conducted  to  the 
ganglion  geniculi  of  the  facial  nerve. 

Middle  and  Accessory  Meningeal  Arteries. — The  entrance 
,of  the  middle  meningeal  artery  through  the  foramen  spinosum 
should  now  be  examined.  It  gives  minute  twigs  to  the 
semilunar  ganglion,  and  one — the  petrosal  artery — which 
accompanies  the  great  superficial  petrosal  nerve  into  the 
hiatus  canalis  facialis.  The  further  course  of  the  middle 
meningeal  artery  has  been  described  already  (pp.  220). 
The  nervus  spinosus  of  the  mandibular  nerve  also  enters 
the  cranium  through  the  foramen  spinosum  (p.  275). 

The  accessory  meningeal  artery  enters  the  cranium  through 
the  foramen  ovale,  and  is  distributed  chiefly  to  the  semilunar 
ganglion. 


DISSECTION  OF  THE  ORBIT. 

Within    the    orbital    cavity    the    following    structures    are 
grouped  around  the  eyeball  and  the  optic  nerve : — 

'Rectus  superior. 

Rectus  inferior. 

Rectus  lateralis. 
Muscles,  .     A  Rectus  medialis. 

Obliquus  superior. 

Obliquus  inferior. 
\^ Levator  palpebrce  superioris. 
[Ophthalmic  artery  and  its  branches. 
Vessels,     .     .  \  Ophthalmic  veins  (superior  and  inferior)  with  their  tribu- 
[         taries. 


334  HEAD  AND  NECK 

^Oculo-motor  (3rd  cerebral). 
Trochlear  (4th  cerebral). 
Abducent  (6th  cerebral). 

Nerves,     .     .-{  -r       •     ',  I  from  ophthalmic  division  of  the  trigeminal 

j_jacrimai,  y  j^r^.!  ^     ^ 

-.J         .,.'  or  filth  cerebral  nerve. 

Naso-ciliary,  ) 

Zygomatic  branch  of  the    maxillary   division  of  the    tri- 
geminal nerve. 
Ciliary  ganglion. 
Lacrimal  gland. 
Fascia  Bulbi. 

Dissection.  — The  roof  of  the  orbit  must  be  removed  with  the  aid  of  the 
saw,  the  chisel,  and  the  bone  forceps.  Begin  by  removing  the  thick  cranial 
wall  above  the  orbital  opening,  leaving  only  a  thin  portion  corre- 
sponding to  the  superior  orbital  arch.  Whilst  this  is  being  done, 
care  should  be  taken  to  preserve  the  soft  parts  of  the  forehead  and  the 
upper  eyelid.  It  is  of  great  advantage  to  retain,  throughout  the  whole 
examination  of  the  orbital  cavity,  the  bony  ring  which  constitutes  its  opening 
on  the  face.  The  thin  roof  of  the  orbit  may  next  be  removed  with  the 
chisel  and  bone  forceps.  The  lesser  wing  of  the  sphenoid,  where  it  forms 
the  upper  boundary  of  the  superior  orbital  fissure,  should  be  taken  away 
by  the  bone  forceps,  but  the  dissector  should  carefully  preserve  intact  the 
ring  of  bone  around  the  optic  foramen.  The  superior  orbital  fissure  is 
now  fully  opened  up,  and  the  various  nerves,  as  they  enter  the  orbit  from 
the  cavernous  sinus,  may  be  followed  out.  Lastly,  the  anterior  clinoid 
process  may  be  taken  away  with  advantage. 

Periosteum.  —  If  the  dissection  has  been  successfully 
carried  out,  the  periosteum  clothing  the  under  surface  of  the 
orbital  roof  will  be  exposed  uninjured.  The  periosteum  of 
the  orbit  forms  a  funnel-shaped  sheath,  which  encloses  all  the 
contents  of  the  cavity  except  the  zygomatic  nerve,  and  is  but 
loosely  attached  to  its  bony  walls.  Posteriorly  it  is  directly 
continuous,  through  the  superior  orbital  fissure,  with  the 
dura  mater.  Expanding  with  the  cavity,  it  becomes  con- 
tinuous anteriorly,  around  the  orbital  opening,  with  the 
periosteum  which  clothes  the  exterior  of  the  skull.  Here 
also  it  presents  important  connections  with  the  palpebral 
fascia. 

Reflection  of  the  Periosteum  and  the  subsequent  Dissection. — The 

periosteum  should  be  divided  along  the  middle  line  of  the  orbit,  and  then 
transversely  close  to  the  orbital  opening.  It  can  now  be  thrown  medially 
and  laterally.  When  this  is  done,  the  lacrimal  gland  will  be  exposed  in  the 
antero-lateral  part  of  the  cavity.  Further,  the  large  frontal  nerve,  lying 
upon  the  upper  surface  of  the  levator  palpebrae  superioris,  will  be  seen  in  the 
middle  line  of  the  orbit ;  as  it  approaches  the  anterior  part  of  the  cavity 
it  is  joined  by  the  supra-orbital  artery.  The  other  superficial  structures 
are  usually  more  or  less  obscured  by  the  soft  pliable  fat,  which  every- 
where fills  up  the  interstices  between  the  different  orbital  contents.  On 
carefully  separating  this,  along  the  medial  wall  of  the  orbit,  the  superior 
oblique  muscle  will  be  more  fully  displayed,  and  lying  upon  and  entering 


DISSECTION  OF  THE  ORBIT 


335 


the  posterior  part  of  this  muscle  the  small  trochlear  or  fourth  cerebral  nerve 
will  be  discovered.  The  dissector  often  fails  to  find  this  nerve,  because  as 
a  general  rule  he  looks  for  it  too  far  forwards.  Lastly,  the  lacrimal  nerve 
and  artery  will  be  found,  running  along  the  lateral  wall  of  the  orbit,  above 
the  level  of  the  upper  margin  of  the  lateral  rectus  muscle. 

These  structures  must  be  thoroughly  cleaned  and  isolated  by  the  removal 
of  the  fat  from  around  them.  As  the  superior  oblique  muscle  is 
followed  anteriorly  it  will  be  found  to  end  in  a  slender  tendon,  which 
passes  through  a  ring-like  pulley  attached  to  the  medial  angular  process  of 


Lacrimal  g 


Frontal  nerve 
Short  ciliary 


Ophthalmic  nerve 


Infra-trochlear  nerve 

Supra-trochlear  nerve 
Supra-orbital  nerve 

Anterior  ethmoidal  nerve 

Long  ciliary  nerves 

Naso-ciliary  nerve 
Ciliary  ganglion 

Optic  nerve 


Maxillary  nerve 

Motor  root  of  trigeminal 

"" Mandibular  nerve 

'"-Semilunar  ganglion  (thrown  laterally) 


Fig.  133.— The  Ophthalmic  Nerve  of  the  Left  Side.      The  semilunar  ganglion 
and  the  nerves  have  been  everted  and  turned  over  to  show  the  motor  root. 

the  frontal  bone.  This  pulley  must  be  defined,  and  the  tendon  of  the 
muscle  followed  laterally  from  it  to  its  insertion  into  the  eyeball.  Note  that 
the  levator  palpebrce  superioris  Hes  upon  the  upper  surface  of  the  superior 
rectus,  and,  if  it  is  raised,  a  nerve  twig  will  be  noticed  emerging  from  the 
substance  of  the  rectus  superior  for  the  supply  of  the  levator  palpebrce 
muscle.     This  is  a  branch  of  the  superior  division  of  the  third  nerve. 

The  dissection  of  the  above  parts  will  be  facilitated  by  grasping  the 
anterior  part  of  the  eyeball  with  the  forceps  and  drawing  it  forwards.  It 
may  be  retained  in  this  position  by  running  a  fine  needle  and  thread  through 
the  ocular  conjunctiva  and  stitching  it  to  the  nose.  In  doing  this,  however, 
take  care  that  the  needle  does  not  penetrate  the  cornea,  because  this  might 
render  the  subsequent  inflation  of  the  eyeball  impossible. 


336  HEAD  AND  NECK 

Nervus  Frontalis. — The  frontal  nerve  is  the  continuation 
of  the  stem  of  the  ophthalmic  division  of  the  trigeminal 
nerve,  after  it  has  given  off  its  lacrimal  and  naso-ciliary 
branches.  It  enters  the  orbit  through  the  superior  orbital 
fissure,  above  the  muscles,  and  runs  anteriorly  upon  the  upper 
surface  of  the  levator  palpebrse  superioris,  immediately  sub- 
jacent to  the  periosteal  lining  of  the  orbital  cavity.  It  ends 
at  a  variable  distance  from  the  orbital  opening  by  dividing 
into  the  supra-orbital  and  supra-trochlear  branches. 

The  supra-trochlear  nerve  is  the  medial  and  smaller  of  the 
two  terminal  branches  of  the  frontal.  It  runs  towards  the 
trochlea  of  the  superior  oblique  muscle,  above  which  it  pierces 
the  palpebral  fascia,  leaves  the  orbit,  and  turns  round  the 
orbital  arch  to  reach  the  forehead.  Its  further  course  has 
been  described  already  (p.  156).  In  the  orbit  it  gives  off 
one  small  twig  close  to  the  pulley  of  the  superior  oblique 
muscle.  This  passes  downwards  to  join  the  infra-trochlear 
branch  of  the  naso-ciliary  nerve. 

The  supra-orbital  nerve  is  continued  onwards,  in  the  line 
of  the  parent  stem,  and,  passing  through  the  supra-orbital 
notch  or  foramen,  it  turns  upwards  on  the  forehead  (p. 
156).  In  the  dissection  of  the  scalp  this  nerve  has  been 
seen  to  divide  into  a  lateral  and  a  medial  division.  Some- 
times the  separation  takes  place  within  the  orbit,  and  in 
that  case  the  larger  lateral  part  occupies  the  supra-orbital 
notch. 

Nervus  Lacrimalis. — This  is  the  smallest  of  the  terminal 
branches  of  the  ophthalmic  division  of  the  fifth.  It  enters 
the  orbit  through  the  superior  orbital  fissure,  above  the  level 
of  the  muscles,  and  runs  anteriorly,  along  the  lateral  wall  of 
the  cavity,  above  the  upper  margin  of  the  lateral  rectus 
muscle.  At  the  anterior  part  of  the  orbit  it  continues  its 
course,  under  cover  of  the  lacrimal  gland,  until  it  reaches 
the  lateral  part  of  the  upper  eyelid,  in  which  it  ends  (p.  137). 
Within  the  orbital  cavity  it  gives  numerous  twigs  to  the  deep 
surface  of  the  lacrimal  gland,  and  sends  downwards  a  filament 
which  connects  it  with  the  zygomatic  branch  of  the  maxillary 
nerve. 

Nervus  Trochlearis. — The  small  fourth  nerve  is  destined 
entirely  for  the  supply  of  the  superior  oblique  muscle.  Having 
entered  the  orbit  through  the  superior  orbital  fissure,  above  the 
muscles,  it  passes  antero-medially,  under  the  periosteum,  and 


DISSECTION  OF  THE  ORBIT  337 

finally  sinks  into  the  upper  or  orbital  surface  of  the  superior 
oblique  muscle  not  far  from  its  origin. 

GlandulaLacrimalis. — The  lacrimal  gland  is  asmall,  flattened 
and  distinctly  lobular  structure  of  oval  form,  which  is  placed 
transversely  in  the  antero-lateral  part  of  the  orbit.  It  con- 
sists of  two  parts  or  groups  of  lobules — a  superior  and  an 
inferior — imperfectly  separated  from  each  other.  The  glaiidula 
lacrimaHs siiJ>erior,\\hic\i  constitutes  the  main  mass  of  the  gland, 
lies  in  the  orbital  cavity.  Its  lateral  convex  surface  is  lodged 
in  a  hollow  upon  the  medial  aspect  of  the  zygomatic  process 
of  the  frontal  bone,  and  it  is  bound  to  the  lateral  part  of  the 
orbital  arch  by  short  fibrous  bands  which  proceed  from  the 
periosteum.  The  deep  or  medial  surface  is  slightly  concave, 
and  rests  upon  the  levator  palpebr^  superioris  and  lateral 
rectus,  which  interv^ene  between  it  and  the  eyeball.  The 
gla7idula  lacn77iaUs  inferior  lies  below  and  anterior  to  the 
superior  part,  from  which  it  is  partially  separated  by  the  ex- 
panded tendon  of  the  levator  palpebrse  superioris.  It  projects 
into  the  base  of  the  upper  eyelid,  and  rests  upon  the  con- 
junctiva which  lines  the  under  aspect  of  the  lid.  This  portion 
of  the  gland  has  been  already  examined  in  the  dissection  of 
the  eyelids  (p.  138).  Even  in  the  undissected  subject  it  can 
be  seen  through  the  conjunctiva  when  the  upper  eyelid  is 
fully  everted. 

The  lacrimal  gland  secretes  the  tears,  and  its  ducts 
(three  to  five  from  the  superior  part  and  three  to  nine  from 
the  inferior  part)  open  upon  the  under  surface  of  the  upper 
eyelid  in  the  neighbourhood  of  the  fornix  (Fig.  64). 

Musculus  Levator  Palpebrae  Superioris. — This  muscle  rests 
upon  the  upper  surface  of  the  rectus  superior.  Posteriorly, 
it  is  narrow  and  pointed,  but  it  expands  as  it  passes  above 
the  eyeball  to  reach  the  upper  eyelid.  It  arises  from  the  under 
surface  of  the  roof  of  the  orbit  immediately  anterior  to  the 
optic  foramen,  and  in  the  anterior  part  of  the  orbital  cavity 
it  widens  out  into  a  broad  membranous  expansion,  the  con- 
nections of  which  have  been  described  already  (p.  136).  The 
lateral  and  medial  margins  of  this  expansion  are  fixed  to  the 
rim  of  the  orbital  opening,  in  close  proximity  to  the  liga- 
mentum  palpebrale  mediale  and  the  raphe  palpebralis  lateralis. 
By  these  attachments  excessive  action  of  the  muscle  upon  the 
upper  eyelid  is  in  a.  measure  checked. 

Dissection. — Divide  the  frontal  nerve  and  throw  the  ends  anteriorly  and 
VOL.  II — 22 


33^ 


HEAD  AND  NECK 


posteriorly.  The  levator  palpebrse  superioris  also  may  be  cut  midway 
between  its  origin  and  insertion.  On  raising  the  posterior  portion  a 
minute  nerve  twig  will  be  seen  entering  its  deep  or  ocular  surface. 
This  comes  from  the  superior  division  of  the  third  or  oculo-motor  nerve. 

The  eyeball  should  now  be  inflated.  This  may  be  done  from  the 
front  or  from  behind.  If  the  latter  method  is  selected,  gently  separate 
the  fat  under  cover  of  the  superior  rectus  muscle,  and  push  the  ciliary 
vessels  and  nerves  away  from  the  optic  nerve.  Next  make  a  small  incision 
through  the  sheath  of  the  nerve.  Pass  a  ligature  round  the  nerve  anterior 
to  the  opening,  and  then  pass  a  blowpipe,  provided  with  a  stylet,  through 
the  incision  and  along  the  nerve  into  the  interior  of  the  eyeball.  When  the 
globe  of  the  eye  is  fully  inflated,  the  ligature  may  be  tightened  as  the  blow- 
pipe is  withdrawn.     A  very  much  better  plan,  however,  is  to  inflate  the 

eyeball  from  the  front.  For  this 
purpose  make  an  oblique  valvular 
aperture  in  the  sclero-corneal  junc- 
tion, with  the  point  of  a  sharp 
narrow -bladed  knife.  Through 
this  the  blow-pipe  may  be  intro- 
duced, and  on  its  withdrawal  after 
the  inflation  of  the  eyeball  the 
valvular  character  of  the  opening 
is  sufficient  to  prevent  the  escape 
of  the  air. 

Posterior  to  the  eyeball  the  dis- 
sector will  notice  a  quantity  of 
loose  bursal- like  tissue.  This  is 
the  fascia  bulbi  (O.T.  capstile  of 
Tenon).  Seize  the  upper  part  of 
this  with  the  forceps,  and  remove 
a  small  portion  with  a  pair  of 
scissors.  An  aperture  is  thus 
made  into  the  fascia,  and  the 
handle  of  the  knife  can  be  intro- 
duced into  the  space  between  it 
and  the  eyeball.  In  favourable 
cases  the  extent  of  the  fascia  can  be  gauged,  and  perhaps  even  the  pro- 
longations or  sheaths  which  it  gives  to  the  tendons  of  the  ocular  muscles 
may  be  made  out.     The  description  of  the  fascia  bulbi  is  given  on  p.  347. 

Musculus  Rectus  Superior. — The  rectus  superior,  which 
lies  under  cover  of  the  levator  palpebrse  superioris,  is  now 
fully  exposed.  It  arises  from  the  upper  margin  of  the  optic 
foramen,  passes  anteriorly  above  the  optic  nerve,  and  ends 
upon  the  upper  aspect  of  the  eyeball  in  a  thin,  delicate  tendon, 
which  expands  somewhat  to  be  inserted  into  the  sclera  about 
three  or  four  lines  posterior  to  the  sclero-corneal  junction. 
It  is  supplied  by  a  branch  from  the  superior  division  of  the 
oculo-motor  nerve.  . 

Musculus  Obliquus  Superior. — This  muscle  arises  from  the 
roof  of  the  orbit  immediately  anterior  to  the  upper  and 
medial  part  of  the  optic  foramen.     It  passes  anteriorly,  along 


of   the    Superior 
From    Hermann 


Fig.    134.  —  Diagram 
Oblique    Muscle. 
Meyer. ) 

a.  Trochlea  and  synovial  sheath. 


DISSECTION  OF  THE  ORBIT  339 

the  medial  wall  of  the  cavity  above  the  medial  rectus.  At 
the  anterior  part  of  the  orbit  it  ends  in  a  slender  tendon, 
which  enters  the  trochlea  and  at  once  changes  its  direction, 
proceeding  postero-laterally,  upon  the  upper  surface  of  the 
eyeball,  under  cover  of  the  superior  rectus.  Beyond  the 
lateral  edge  of  the  superior  rectus  the  tendon  expands  some- 
what, and  is  inserted  into  the  sclera  midway  between  the 
entrance  of  the  optic  nerve  and  the  cornea. 

The  trochlea  or  pulley  through  which  the  tendon  passes  is 
a  small  fibro-cartilaginous  ring,  which  is  attached  by  fibrous 
tissue  to  the  trochlear  fossa — a  depression  in  the  frontal  bone 
close  to  the  medial  angular  process.  The  pulley  is  lined  with 
a  synovial  sheath  which  facilitates  the  movement  of  the 
tendon,  and  from  its  lateral  margin  it  gives  a  fibrous  invest- 
ment to  the  tendon. 

Dissectioti.—V)W\^^  the  superior  rectus  midway  between  its  origin  and 
its  insertion,  and  reflect  the  cut  ends.  On  raising  the  posterior  part  of 
the  muscle  the  superior  division  of  the  oculo-motor  nerve  is  brought  into 
view,  as  it  sinks  into  the  deep  or  ocular  surface  of  the  muscle.  It 
sends  a  twig  to  the  levator  palpebrae  superioris.  The  removal  of  some 
fat  will  bring  the  optic  nerve  more  fully  into  view.  At  the  posterior  part  of 
the  orbit  three  structures  will  be  seen  crossing  the  optic  nerve— viz.,  (i)  the 
naso-ciliary  nerve  ;  (2)  the  ophthalmic  artery ;  and  (3)  the  superior 
ophthalmic  vein.  These  should  be  carefully  cleaned  and  their  branches 
followed  out.  From  the  naso-ciliary  nerve  one  or  two  delicate  thread- 
like branches— the  long  ciliary  yzefves—wiW  be  found  passing  along  the 
optic  nerve  to  reach  the  eyeball.  The  s/ior^  ciliary  nerves,  much  more 
numerous,  accompany  the  long  ciliary  branches,  and  can  readily  be  dis- 
engaged from  the  fat  which  surrounds  the  optic  nerve.  A  strong  member 
of  this  group  should  be  selected  and  followed  posteriorly  ;  it  will  lead  the 
dissector  to  the  ciliary  ganglion.  This  is  a  minute  body  which  is  situated 
upon  the  lateral  side  of  the  optic  nerve  in  the  posterior  part  of  the  orbit. 
With  a  little  patience  and  care  the  roots  which  the  naso-ciliary  nerve  and 
inferior  division  of  the  oculo-motor  nerve  give  to  this  ganglion  can  be 
isolated,  and  perhaps  even  the  sympathetic  root  from  the  internal  carotid 
plexus  will  be  found. 

Nervus  Opticus. — The  optic  nerve  enters  the  orbit  through 
the  optic  foramen.  It  carries  with  it  a  strong  loose  sheath 
of  dura  mater,  and  also  more  delicate  investments  from 
the  arachnoid  and  pia  mater.  The  ophthalmic  artery,  which 
accompanies  it,  lies  on  its  infero-lateral  aspect.  Within  the 
orbit  the  nerve  inclines  antero  -  laterally,  and  at  the  same 
time  somewhat  downwards,  to  the  back  of  the  eyeball,  where 
it  pierces  the  sclera  a  short  distance  to  the  medial  side  of 
its  centre.  The  dissector  has  noted  already  that  the 
ophthalmic  artery  and  vein  and  the  naso-ciliary  nerve  cross 


340  HEAD  AND  NECK 

above  the  optic  nerve,  and  that  it  is  closely  accompanied  by 
the  delicate  ciliary  nerves  and  vessels.  The  optic  nerve  is 
slightly  longer  than  the  distance  which  it  has  to  run  from  the 
optic  foramen  to  the  globe  of  the  eye,  so  that  the  movements 
of  the  eyeball  may  not  be  interfered  with.  Within  the  eye- 
ball the  optic  nerve  spreads  out  in  the  retina. 

Nervus  Naso-ciliaris. — The  naso-ciliary  nerve  (O.T.  nasal) 
arises  from  the  ophthalmic  division  of  the  trigeminal  in  the 
anterior  part  of  the  cavernous  sinus.  It  passes  through  the 
superior  orbital  fissure  and  enters  the  orbital  cavity,  between 
the  two  heads  of  the  lateral  rectus  muscle  and  between  the 
two  divisions  of  the  third  nerve.  It  then  inclines  antero- 
medially,  and,  crossing  the  optic  nerve  obliquely,  it  runs 
between  the  medial  rectus  and  superior  oblique  muscles  to 
the  medial  wall  of  the  orbit,  where  it  divides  into  two  ter- 
minal branches  —  viz.,  the  infra-trochlear  and  the  anterior 
ethmoidal  nerves.  In  addition  to  these  it  gives  off  in  the 
orbit  the  following  branches:  (i)  long  root  to  the  ciliary 
ganglion;  (2)  long  ciliary  nerves;  (3)  posterior  ethmoidal 
nerve. 

Radix  Longa  Ganglii  Ciliaris. — This  is  a  very  slender 
filament  which  springs  from  the  naso-ciliary  as  it  enters  the 
orbit  between  the  heads  of  the  lateral  rectus.  It  runs  along 
the  lateral  side  of  the  optic  nerve,  and  enters  the  upper  and 
posterior  part  of  the  ciliary  ganglion. 

Nervi  Ciliares  Longi. — The  two  long  ciliary  branches 
spring  from  the  naso-ciliary  as  it  crosses  the  optic  nerve. 
They  pass  anteriorly,  upon  the  medial  side  of  the  optic 
nerve,  to  reach  the  globe  of  the  eye  where  they  pierce  the 
sclera.  One  of  the  long  ciliary  nerves  very  constantly 
unites  with  one  of  the  short  ciliary  filaments. 

Nervus  Ethmoidalis  Posterior  passes  through  the  posterior 
ethmoidal  foramen  to  the  ethmoidal  cells  and  the  sphenoidal 
air  sinus. 

Nervus  Infratrochlearis. — The  infra-trochlear  branch  runs 
along  the  medial  wall  of  the  orbit  below  the  superior  oblique 
muscle.  After  passing  under  the  trochlea  of  that  muscle  it 
emerges  from  the  orbit  and  appears  upon  the  face,  where  it 
has  been  dissected  already  (p.  128).  Near  the  pulley  it 
receives  a  communicating  twig  from  the  supra-trochlear  nerve. 
Nervus  Ethmoidalis  Anterior. — This  is  the  larger  of  the 
two  terminal   branches  of  the  naso-ciliary  nerve.      It  leaves 


DISSECTION  OF  THE  ORBIT  341 

the  orbit  by  the  anterior  ethmoidal  canal,  and  is  conducted  to 
the  interior  of  the  cranium,  in  which  it  appears  at  the  lateral 
margin  of  the  cribriform  plate  of  the  ethmoid.  The  canal 
in  which  it  runs  can  readily  be  opened  up  with  the  bone- 
forceps  to  expose  the  nerve.  Upon  the  cribriform  plate  it 
turns  anteriorly,  under  the  dura  mater,  and  almost  immedi- 
ately disappears,  through  a  slit-like  aperture  at  the  side  of  the 
crista  galli,  into  the  nasal  cavity.  There  it  gives  internal 
nasal  b?'anches  to  the  mucous  membrane,  and  is  continued 
downwards  upon  the  posterior  aspect  of  the  nasal  bone. 
Finally,  it  emerges  upon  the  face,  as  the  external  nasal  tierve^ 
by  passing  between  the  lower  margin  of  the  nasal  bone  and 
the  lateral  cartilage  of  the  nose.  Its  terminal  filaments  have 
been  described  already  (p.  140). 

Ganglion  Ciliare  (Fig.  138). — The  ciHary  ganglion  is  a 
small  quadrangular  body,  not  much  larger  than  the  head 
of  a  large  pin.  It  is  placed  in  the  posterior  part  of  the  orbit, 
between  the  optic  nerve  and  the  lateral  rectus  muscle,  and 
very  commonly  on  the  lateral  side  of  the  ophthalmic  artery. 
At  its  posterior  border  it  receives  its  three  roots  ;  whilst  from 
its  anterior  border  the  short  ciliary  nerves  are  given  off. 

The  sensory  root  comes  from  the  naso-ciliary,  and  is  called 
the  lo7ig  root.  The  short  or  motor  root  is  a  short,  stout  trunk  ; 
it  comes  from  the  branch  of  the  oculo-motor  nerve  which 
goes  to  the  inferior  oblique  muscle.  The  sy7?ipathetic  root 
comes  from  the  internal  carotid  plexus,  it  joins  the  ganghon, 
close  to  the  entrance  of  the  long  root  from  the  naso-ciliary 
nerve.  In  some  cases  it  joins  the  long  root  before  it  reaches 
the  ganglion. 

Nervi  Ciliai-es  Breves. — The  short  ciliary  nerves  are  from 
four  to  six  in  number.  They  come  off  in  two  groups,  superior 
and  inferior.  The  lower  nerves  are  generally  more  numerous 
than  the  upper.  As  these  fine  nerves  pass  along  the  optic 
nerve  they  divide  and  thus  increase  in  number ;  at  the  back 
of  the  eyeball  from  twelve  to  eighteen  may  be  counted. 
Finally  they  pierce  the  sclera  by  a  series  of  apertures  which 
are  placed  around  the  entrance  of  the  optic  nerve. 

Arteria  Ophthalmica. — The  ophthalmic  artery  is  a  branch 
of  the  internal  carotid.  It  accompanies  the  optic  nerve 
into  the  orbit  through  the  optic  foramen.  At  first  it  lies 
below  the  optic  nerve,  but  soon  winds  round  its  lateral  side, 
and,   crossing  above  it,   passes   anteriorly  along    the    medial 

II— 22  a 


342 


HEAD  AND  NECK 


wall  of  the  orbit,  below  the  superior  oblique  muscle.  At  the 
medial  side  of  the  orbit  it  ends  by  dividing  into  two  terminal 
branches — viz.,  the  frontal  and  the  dorsal  nasal  (Fig.  136). 

The  branches  of  the  ophthalmic  artery  are  very  numerous, 
and  they  can  seldom  be  satisfactorily  displayed,  unless  a 
special  injection  has  been  made.      They  are : — 


1.  Lacrimal. 

2.  Muscular. 

3.  Arteria  centralis  retinae. 


4.  Ciliary. 

5.  Supra-orbital. 

6.  Ethmoidal . 


7.  Palpebral. 

8.  Dorsal  nasal. 

9.  Frontal. 


Arteria    Lacrimalis. — The    lacrimal    branch    accompanies 
the  lacrimal  nerve,  and  supplies  the  gland  of  that  name  and 


Cornea 


Sinus  venosus  sclerae-  . 

Anterior  ciliary, 
arterv 


Sclera. 


Vena  vortico?a 


Long  posterior 
ciliary  artery 


Anterior  ciliary 
artery 

Ciliary  muscle 


Long  posterior 
ciliary  artery 

Vena  vorticosa 


Long  posterior 
ciliary  artery 


Fig.  135. — Dissection  of  the  Eyeball  showing  the  Arrangement 
of  the  Ciliary  Nerves  and  Vessels. 

the  conjunctiva.  In  each  eyelid  an  arterial  arch,  the  arc  us 
tarseus,  is  formed  by  the  anastomoses  of  the  two  lateral 
palpebral  branches  of  the  lacrimal  with  the  two  medial 
palpebral  branches  of  the  ophthalmic. 

Rami  Musculares  come  off  at  variable  points,  not  only 
from  the  main  artery,  but  also  from  certain  of  its  branches. 
They  supply  the  muscles  contained  in  the  orbital  cavity. 

The  Arteria  Centralis  Retince  is  a  minute  but  important 
artery.  It  pierces  the  infero  -  medial  surface  of  the  optic 
nerve,  about  half  an  inch  posterior  to  the  eyeball,  and 
passes,  in  its  substance,  to  the  interior  of  the  globe  of 
the  eye. 

Arterice    Ciliares   are   very   numerous.       Two    groups    are 


DISSECTION  OF  THE  ORBIT 


343 


recognised — viz.,  a  posterior  and  an  anterior.  The  posterior 
ciliary  arteries  ran  with  the  ciliary  nerves.  They  arise  as 
two  trunks  which  spring  from  the  ophthalmic  whilst  it  lies 
below  the  optic  nerve.  These  divide  into  several  slender 
branches,  which  pierce  the  sclera  around  the  entrance 
of  the  optic  nerve.  Two  members  of  this  group  of  vessels 
enter  the  eyeball  on  either  side  of  the  optic  nerve,  somewhat 


Medial  palpebral 
Dorsal  nasal 
Frontal 


Infra-trochlear  nerve 

Anterior  ethmoidal 
artery  and  nerve 


Posterior  ciliary 

Posterior  ethmoidal 

Ophthalmic 


Lateral 
palpebral 


Supra-orbital 


Arteria  centralis 
retinae 


Posterior  ciliary 

Muscular 

Lacrimal 


Ophthalmic 

"Naso-clliary  nerve 
"Internal  carotid 


Fig.  136.— Diagram  of  the  Ophthalmic  Artery  and  its  Branches. 
(After  Quain  and  Meyer,  modified. ) 


They   are   termed    arterice    ciliares 
35).      The  arterice    ciliares  anterior es 


apart    from   the    others. 

posteriores    longce    (Fig.  i 

come  off,  in  the  anterior  part  of  the  orbit,  from  the  lacrimal 
and  muscular  branches.  They  vary  in  number  from  six  to 
eight,  and  run  to  the  anterior  part  of  the  eyeball,  where  they 
form  an  arterial  circle  under  the  conjunctiva.  Finally,  they 
pierce  the  sclera  immediately  posterior  to  the  cornea. 

Arteria  Supraorbitalis. — This  accompanies  the  supra-orbital 
nerve  to  the  forehead,  where  it  was  dissected  at  a  previous 
stage  (p.  157). 


344  HEAD  AND  NECK 

Arterice  Ethmoidales. — There  are  two  ethmoidal  branches, 
an  anterior  and  a  posterior  :  they  pass  through  the  anterior 
and  posterior  ethmoidal  foramina  on  the  medial  wall  of  the 
orbit.  The  arteria  ethmoidalis  posterior  supplies  the  mucous 
lining  of  the  posterior  ethmoidal  cells,  and  sends  twigs  to  the 
upper  part  of  the  nose.  The  arteria  ethmoidalis  anterior  is 
a  larger  branch.  It  runs  in  company  with  the  anterior 
ethmoidal  nerve,  and  gives  off  minute  twigs  at  each  stage  of 
its  course.  Thus  in  the  anterior  ethmoidal  foramen  it  gives 
branches  to  the  mucous  lining  of  the  anterior  ethmoidal  cells 
and  the  frontal  sinus ;  during  its  short  sojourn  in  the  cranial 
cavity  it  gives  off  a  small  arteria  meningea  anterior;  in  the 
nasal  cavity  it  gives  twigs  to  the  mucous  membrane.  Its 
terminal  branch  appears  on  the  face  and  supplies  the  side  of 
the  nose. 

Arteria  Dorsalis  Nasi. — The  dorsal-  artery  of  the  nose  is 
distributed  at  the  root  of  the  nose,  and  anastomoses  with 
the  angular  branch  of  the  external  maxillary  artery. 

Arteria  Frontalis. — This  accompanies  the  supra-trochlear 
nerve  to  the  forehead,  where  it  has  been  dissected  already 

(P-  157)- 

Vense  Ophthalmicae. — As  a  general  rule  there  are  two 
ophthalmic  veins,  superior  and  inferior.  The  superior 
ophthalmic  vein  is  the  larger  of  the  two  and  it  accompanies 
the  artery.  It  takes  origin  at  the  root  of  the  nose,  where 
it  communicates  with  the  angular  vein.  The  inferior 
ophthalmic  vein  lies  below  the  level  of  the  optic  nerve,  and 
it  is  brought  into  communication  with  the  pterygoid  venous 
plexus  by  an  offset'  which  passes  through  the  inferior  orbital 
fissure.  The  two  ophthalmic  veins  receive  numerous  tribu- 
taries during  their  course  through  the  orbit ;  finally  they 
pass  between  the  two  heads  of  the  lateral  rectus  muscle,  and 
through  the  superior  orbital  fissure  to  open  into  the  cavernous 
sinus,  either  separately  or  by  a  common  trunk. 

Musculi  Recti  Oculi. — The  four  straight  muscles  of  the 
eyeball  diverge  from  the  apex  of  the  orbit.  They  form  the 
sides  of  a  four-sided  or  pyramidal  space  in  which  are  en- 
closed the  optic  nerve  and  the  greater  part  of  the  globe  of 
the  eye.  The  rectus  superior.,  which  has  been  reflected,  has 
been  studied  already.  The  rectus  medialis  springs  from  the 
medial  side  of  the  optic  foramen,  and  the  rectus  inferior  takes 
origin  from  a  fibrous  band  which  bounds  the  media'l  end  of  the 


DISSECTION  OF  THE  ORBIT 


345 


superior  orbital  fissure.  The  rectus  lateralis  is  distinguished 
from  the  others  by  arising  from  a  fibrous  arch,  the  extremities 
of  which  are  termed  its  two  heads  of  origin.  The  lower 
head  arises  in  common  with  the  rectus  inferior  from  the 
body  of  the  sphenoid,  where  this  bounds  the  medial  end  of 
the  superior  orbital  fissure ;  the  upper  head  is  attached  above 
the  superior  orbital  fissure  upon  the  lateral  side  of  the  optic 
foramen,  where  its  origin  becomes  continuous  with  the 
superior  rectus.  Through  the  archway  which  intervenes 
between    the    two  heads  of   the  lateral  rectus  pass  the  two 


Frontal  nerve 


Lacrimal  nerve 


Fourth  nerve    L 

Naso-ciliary  | 
nerve 


Lateral  rectus 

Sixth  nerve 
Inferior  orbital  fissure 


superior  rectus 

Levator  palpebrae 
superioris 
./     Superior  division  of 
third  nerve 

,v-^^Fourth  nerve 


Superior  oblique 


Optic  foramen 


Medial  rectus 


Inferior  rectus 

Inferior  division  of 
third  nerve 


Fig.  137. — Diagram  of  the  Orbital  Cavity,  and  of  the  origin  of  the  ocular 
muscles  in  relation  to  the  optic  foramen  and  the  superior  orbital  fissure, 
and  the  nerves  that  traverse  the  latter. 


divisions  of  the  oculo-motor  nerve,  the  naso- ciliary  nerve,  the 
abducent  nerve,  and  the  ophthalmic  veins  (Fig.  137). 

A  better  view  of  these  attachments  may  be  obtained  by  dividing   the 
optic  nerve  close  to  the  optic  foramen  and  turning  the  eyeball  anteriorly. 

The  manner  in  which  the  recti  muscles  are  inserted  into 
the  eyeball  should  next  be  studied.  Each  ends  in  a  deUcate 
membranous  tendon,  which  is  inserted  into  the  sclera,  about 
a  quarter  of  an  inch  posterior  to  the  sclero-corneal  junction. 

Nervus  Oculomotorius. — The  two  divisions  of  this  nerve 
enter  the  orbit  through  the  superior  orbital  fissure,  between 
the  two  heads  of  the  lateral  rectus.      The  superior  divisio?i  has 


346  HEAD  AND  NECK 

been  traced  to  the  rectus  superior  and  the  levator  palpebrae 
superioris.  The  inferior  division  is  larger.  It  almost  im- 
mediately divides  into  three  branches  for  the  supply  of  the 
rectus  medialis,  the  rectus  inferior,  and  the  obliquus  inferior. 
The  nerves  to  the  two  recti  enter  the  ocular  surfaces  of  the 
muscles ;  the  nerve  to  the  inferior  oblique  is  prolonged 
anteriorly,  in  the  interval  between  the  rectus  inferior  and 
rectus  lateralis,  and  enters  the  posterior  border  of  the  inferior 
oblique  muscle.  Soon  after  its  origin  this  branch  gives  the 
short  motor  root  to  the  ciliary  ganglion, 

Nervus  Abducens. — The  sixth  nerve  will  be  found  closely 
applied  to  the  ocular  surface  of  the  lateral  rectus.  It  enters 
the  orbit  through  the  narrow  interval  between  the  heads  of 
lateral  rectus  muscle  and  it  supplies  this  muscle  only. 

Arrangement  of  the  Nerves  in  the  Superior  Orbital 
Fissure. — When  the  orbit  is  dissected,  and  the  various  nerves 
met  with  in  the  dissection  of  the  cavernous  sinus  are  traced 
into  the  cavity,  the  dissector  will  note  that  the  arrangement  of 
the  nerves  in  the  superior  orbital  fissure  is  somewhat  different 
from  that  in  the  sinus. 

The  lacrimal,  frontal,  and  trochlear  nerves  enter  the  orbit 
above  the  muscles  on  very  much  the  same  plane  (Fig.  137). 
The  other  nerves  enter  between  the  heads  of  the  lateral 
rectus.  Of  these  the  superior  division  of  the  oculo-motor 
nerve  is  the  highest,  next  comes  the  naso-ciliary  nerve,  then 
the  inferior  division  of  the  oculo-motor  nerve,  and  the 
abducent  nerve  occupies  the  lowest  level. 

Dissection.  — The  inferior  oblique  muscle  is  placed  very  differently  from 
the  other  muscles  of  the  orbit.  It  is  situated  below  the  eyeball,  running 
below  its  inferior  surface  to  gain  its  lateral  surface.  It  must  be  dissected 
from  the  front.  It  is  necessary,  therefore,  to  restore  the  eyeball  to  its 
natural  place.  Next,  evert  the  lower  eyelid  and  remove  the  conjunctiva 
from  its  deep  surface  as  it  is  reflected  on  to  the  globe  of  the  eye.  A  little 
dissection  in  the  floor  of  the  anterior  part  of  the  orbit  and  the  removal  of 
some  fat  will  reveal  the  inferior  oblique  muscle. 

Musculus  Obliquus  Inferior. — ^This  muscle  arises  from  a 
small  depression  on  the  orbital  surface  of  the  maxilla, 
immediately  lateral  to  the  opening  of  the  naso-lacrimal  duct. 
It  passes  laterally,  below  the  inferior  rectus  muscle,  and, 
inclining  slightly  posteriorly,  ends  in  a  thin  membranous 
tendon,  which  gains  insertion  into  the  lateral  aspect  of  the 
sclera  of  the  eyeball  under  cover  of  the  rectus  lateralis.  The 
insertion  is  not  far  from   that   of  the  superior   oblique,   but 


DISSECTION  OF  THE  ORBIT 


347 


is  placed  more   posteriorly.      It  is    supplied   by  the   i?iferior 
division  of  the  third  nerve. 

Fascia  Bulbi  (O.T.  Capsule  of  Tenon). — The  connections 
of  the  fibrous  sheath  of  the  eyeball  are  somewhat  com- 
plicated, and  they  cannot  be  satisfactorily  displayed,  in  every 
detail,  in  an  ordinary  dissection.      The  fascia  may  be  studied 


l,evator  palpebrae  superior 
Superior  rec 

Superior  oVjlique — 


Lacrimal  gland  • 


Lateral  rectus 


Sixth  nerve 


Ciliarj-  ganglion 


Naso-ciliary  nerve    '    --■ 


Ophthalmic  division 

of  fifth  nerve    7 
Maxillary  division 
of  fifth  nerve 

Motor  root  of 
fifth  nerve 


Trochlea 


I Superior  oblique 


Inferior  rectus 
Medial  rectus 


—  Founh  ner%e 
Sixth  nerve 


Opiic  nerve 


Semilunar  ganglion/  / 

Mandibular  division  of  fifth  nerVe 


Sixth  ner^'e 
Fourth  neive 


^Third  nerve 


Fig.  138. — Dissection  of  the  Orbit  and  the  Middle  Cranial  Fossa.      Both 
roots  of  the  fifth  nerve  with  the  semilunar  ganglion  are  turned  laterally. 


from  a  threefold  point  of  view — (i)  in  its  connection  w-ith 
the  eyeball;  (2)  in  its  connections  w^ith  the  muscles  inserted 
into  the  globe  of  the  eye ;  and  (3)  in  its  connections  with 
the  walls  of  the  orbit. 

The  relation  which  the  fascia  bulbi  bears  to  the  eyeball 
is  very  simple.  The  membrane  is  spread  over  the  posterior 
five-sixths  of  the  globe — the  cornea  alone  being  free  from  it. 
Anteriorly,  it  lies  in  relation  with  the  ocular  conjunctiva,  with 
which  it  is   intimately  connected,   and   it   ends  by  blending 


348  HEAD  AND  NECK 

with  the  conjunctiva  close  to  the  margin  of  the  cornea. 
Posteriorly^  it  fuses  with  the  sheath  of  the  optic  nerve  where 
the  nerve  pierces  the  sclera.  The  internal  surface  of  the 
membrane  {i.e.  the  surface  towards  the  globe  of  the  eye)  is 
smooth,  and  is  connected  to  the  eyeball  by  some  soft  yielding 
and  humid  areolar  tissue,  the  interval  between  them  con- 
stituting, in  fact,  an  extensive  lymph  space  called  the  spatium 
interfasciale.  Its  external  surface  is  in  contact  posteriorly 
with  the  orbital  fat,  to  which  it  is  loosely  adherent ;  and  it  is 
firmly  attached  to  the  ocular  conjunctiva  more  anteriorly.  It 
obviously,  therefore,  forms  a  membranous  socket  in  which 
the  eyeball  can  glide  with  the  greatest  freedom. 

The  tendons  of  the  various  ocular  muscles  are  inserted 
into  the  eyeball  within  this  fascia,  and  they  gain  its  interior 
by  piercing  the  membrane  opposite  the  equator  of  the  globe 
(Fig.  139).  The  lips  of  the  openings  through  which  the  four 
recti  muscles  pass  are  prolonged  posteriorly  upon  the  muscles, 
in  the  form  of  sheaths,  very  much  in  the  same  manner  that 
the  infundibuliform  fascia  is  prolonged  upon  the  spermatic 
cord  from  the  abdominal  inguinal  ring.  These  sheaths 
gradually  become  more  and  more  attenuated,  until  at  last 
they  blend  with  the  perimysium  of  the  muscular  bellies.  In 
the  case  of  the  superior  oblique  muscle  the  corresponding 
prolongation  is  related  only  to  its  reflected  portion  ;  when  it 
reaches  the  pulley  it  ends,  by  becoming  attached  to  its 
margins.  The  sheath  of  the  inferior  oblique  may  be  traced 
upon  the  muscle  as  far  as  the  floor  of  the  orbit.  The  medial 
or  ocular  edge  of  each  of  the  four  apertures  through  which 
the  recti  miuscles  pass  is  strengthened  by  a  shp  of  fibrous 
tissue  (Lockwood),  and  as  the  fascia  bulbi  is  firmly  bound  to 
the  bony  wall  of  the  orbit  at  various  points  these  slips  act  as 
pulleys,  and  protect  the  globe  of  the  eye  from  pressure  during 
contraction  of  the  muscles.  The  aperture  for  the  superior 
oblique  is  not  furnished  with  such  a  slip,  and  it  is  doubtful 
if  the  opening  for  the  inferior  oblique  muscle  possesses  one. 

Dissection. — An  admirable  view  of  the  relations  which  the  fascia 
bulbi  presents  to  the  eyeball  and  the  tendons  of  the  ocular  muscles  can 
be  obtained  by  the  following  dissection  : — Divide  the  lateral  commissure  of 
the  eyelid  to  the  margin  of  the  orbital  opening.  Pull  the  eyelids  widely 
apart,  so  as  to  expose  as  much  as  possible  of  the  anterior  face  of  the 
eyeball.  Next  divide  the  conjunctiva  by  a  circular  incision  just  beyond 
the  cornea.  At  this  point  the  fascia  bulbi  is  so  intimately  connected 
with  the  conjunctiva  that  it  is  divided  at  the  same  time.     Now  raise  care- 


DISSECTION  OF  THE  ORBIT 


349 


fully  both  conjunctiva  and  fascia  bulbi  from  the  surface  of  the  eyeball, 
and  spread  them  out  round  the  orbital  opening,  as  is  depicted  in  Fig.  139. 
The  openings  in  the  fascia  bulbi  for  the  tendons  of  the  ocular  muscles 
and  the  thickened  margins  of  these  apertures  are  well  seen.  Note  also  the 
sheaths  which  are  given  to  the  muscles. 

Check  and  Suspensory  Ligaments. — The  connections  of 
the  fascia  bulbi  to  the  walls  of  the  orbital  cavity  are 
somewhat  complicated.  The  suspensory  ligajnent  (Lockwood) 
plays  an  important  part  in  this  respect.  It  stretches  across 
the  anterior  part  of  the  orbit,  after  the  fashion  of  a  hammock, 
and   gives   support   to   the   eyeball.     Its  two  extremities  are 


■Tendon  of  superior  oblique 
Tendon  of  superior  rectus 

Tendon  of  lateral  rectus 

Cut  edge  of  fascia  bulbi 
and  conjunctiva 

Tendon  of  inferior  rectus 


Tendon  of  medial  rectus 

Fig.  139. — Dissection  of  the  Fascia  Bulbi  from  the  front. 


Fascia  bulbi  thrown 
back  from  eyeball 


narrow,  and  are  attached  respectively  to  the  zygomatic  and 
lacrimal  bones.  Below  the  eyeball  it  widens  out  and  blends 
with  the  fascia  bulbi.  The  lateral  and  medial  check  liga??ients 
also  constitute  bonds  of  union  between  the  fascia  bulbi  and 
the  orbital  wall.  They  are  strong  bands  which  pass  from 
the  sheaths  around  the  lateral  and  medial  recti  muscles 
to  obtain  attachment  to  the  zygomatic  and  lacrimal  bones 
respectively,  where  they  are  brought  into  association  with 
the  extremities  of  the  suspensory  ligament.  The  function 
of  the  check  ligaments  is  to  limit  the  contraction  of  the 
medial  and  lateral  recti  muscles,  and  thus  prevent  excessive 
rotation  of  the  eyeball  in  a  lateral  or  medial  direction. 
There  is  a  similar  but  less  direct  provision  by  means  of  which 
the  action  of  the  superior  and  inferior  recti  muscles  is  limited. 


350  HEAD  AND  NECK 

The  action  of  the  former  muscle  is  checked  through  an 
intimate  connection  with  the  levator  palpebrae  superioris  in 
the  anterior  part  of  the  orbit ;  the  action  of  the  inferior  rectus 
is  checked  through  a  connection  with  the  suspensory  ligament. 

Dissection. — In  order  that  the  zygomatic  branch  of  the  maxillary 
division  of  the  trigeminal  nerve  may  be  displayed  in  its  course  through  the 
orbit,  the  orbital  contents  must  be  removed.  The  nerve  will  then  be 
found  in  the  midst  of  a  little  soft  fat  in  the  angle  between  the  floor  and 
lateral  wall  of  the  orbit. 

Nervus  Zygomaticus  (O.T.  Temper o-Malar). — This  small 
nerve  arises,  in  the  infra-temporal  fossa,  'from  the  maxillary 
division  of  the  trigeminal  nerve.  It  enters  the  orbit  by 
passing  through  the  inferior  orbital  fissure  and  almost 
immediately  divides  into  two  terminal  branches  —  the 
zygomatico-temporal  and  the  zygomatico-facial. 

Ramus  Zygomaticotemporalis.  —  This  branch  runs  antero- 
superiorly  upon  the  lateral  wall  of  the  orbit,  under  cover  of  the 
periosteum,  and,  after  receiving  a  communicating  twig  from 
the  lacrimal  nerve,  it  enters  the  zygomatico  -  orbital  canal 
of  the  zygomatic  bone.  This  conducts  it  to  the  anterior  part 
of  the  temporal  region,  where  it  has  been  examined  already 
(pp.  155  and  156).  _ 

Ramus  Zygomaticofacialis. — The  zygomatico-facial  branch 
also  enters  a  zygomatico-orbital  canal,  and  is  finally  con- 
ducted to  the  face  by  the  zygomatico  -  facial  canal  which 
traverses  the  zygomatic  bone  (p.  127). 


PREVERTEBRAL  REGION. 

The  following  are  the  structures  to  be  displayed  in  this 
dissection : — 


Prevertebral  muscles. 
Intertransverse  muscles. 
Cervical  nerves. 
Vertebral  artery. 


Vertebral  vein. 

Vertebral  and  cranio-vertebral 
articulations. 


Dissection. — To  separate  the  anterior  part  of  the  head  with  the  pharynx 
from  the  posterior  part  and  the  vertebral  column  a  somewhat  complicated 
dissection  is  necessary.  Place  the  head  upside  down,  so  that  the  cut  margin 
of  the  skull  rests  upon  the  table  ;  divide  the  common  carotid  artery,  the 
internal  jugular  vein,  the  vagus  nerve,  and  the  sympathetic  trunk,  on 
each  side,  at  the  level  of  the  neck  of  the  first  rib ;  pull  the  trachea 
and  oesophagus,  together  with  the  great  blood  vessels  and  nerves,  away 
from  the  anterior  surface  of  the  vertebral  column.     The  separation  must 


PREVERTEBRAL  REGION  351 

be  effected  right  up  to  the  base  of  the  skull.  At  this  point  great  caution 
must  be  observed,  otherwise  the  pharyngeal  wall  or  the  insertions  of  the 
prevertebral  muscles  will  be  damaged.  The  base  of  the  skull  having  been 
reached,  the  point  of  the  knife  should  be  carried  across  the  basilar  portion 
of  the  occipital  bone,  between  the  pharynx  and  the  prevertebral  muscles, 
to  divide  the  thick  investing  periosteum. 

The  basilar  portion  of  the  occipital  bone  must  now  be  divided  by  means 
of  a  chisel.  Still  retaining  the  part  upside  down,  place  the  skull  so  that  its 
floor  rests  upon  the  end  of  a  wooden  block.  Then  apply  the  edge  of  the 
chisel  to  the  under  surface  of  the  basilar  portion  of  the  occipital  bone, 
adjust  it  accurately  in  the  interval  between  the  pharyngeal  wall  and  the 
prevertebral  muscles,  and  with  a  wooden  mallet  drive  it  through  the  base 
of  the  skull,  inclining  it,  at  the  same  time,  slightly  posteriorly. 

The  next  step  in  the  dissection  consists  in  making  two  saw-cuts  through 
the  cranial  wall.  The  head  having  been  placed  upon  its  side,  the  saw 
must  be  applied  to  the  lateral  aspect  of  the  skull,  half  an  inch  posterior  to 
the  mastoid  process,  and  be  carried  obliquely  antero-medially  to  reach  a 
point  immediately  posterior  to  the  jugular  foramen.  A  similar  saw-cut 
must  be  made  upon  the  opposite  side  of  the  head. 

To  complete  the  dissection  the  dissector  must  again  have  recourse  to  the 
chisel.  Placing  the  preparation  so  that  the  floor  of  the  cranium  looks 
upwards,  divide  the  base  of  the  skull,  on  each  side,  in  the  interval  between 
the  petrous  portion  of  the  temporal  bone  and  the  basilar  portion  of  the 
occipital  bone.  Anteriorly,  this  cut  should  reach  the  lateral  extremity  of 
the  incision  already  made  through  the  basilar  portion  ;  whilst  posteriorly, 
it  should  be  carried  to  the  medial  side  of  the  jugular  foramen  to.  reach 
the  medial  end  of  the  saw-cut.  When  this  has  been  done  upon  both  sides 
of  the  basilar  portion,  the  anterior  part  of  the  skull  carrying  the  pharynx  and 
the  great  blood-vessels  and  nerves  can  be  separated  from  the  posterior  part  of 
the  skull  and  cervical  portion  of  the  vertebral  column.  The  only  large 
nerve  which  will  be  divided  is  the  hypoglossal,  but,  as  it  is  cut  close  to  the 
basis  cranii,  and  above  its  connection  with  the  ganglion  nodosum  of  the 
vagus,  it  retains  its  position. 

The  pharynx  and  anterior  portion  of  the  skull  should  now  be  covered 
with  a  piece  of  cloth  soaked  in  preservative  solution,  and  the  whole 
enveloped  in  an  oil-cloth  wrapper.  It  can  then  be  laid  aside  until  the 
dissection  of  the  prevertebral  region  and  the  ligaments  of  the  cervical 
vertebrae  and  the  occiput  have  been  completed. 

Returning  to  the  posterior  part  of  the  skull  and  the  cervical 
portion  of  the  vertebral  column,  the  dissector  should  proceed 
to  define  the  attachments  of  the  muscles  which  lie  anterior 
to  the  transverse  processes  and  the  bodies  of  the  vertebrce. 
These  are  three  in  number  on  each  side,  viz.  : — 

1.  The  longus  colli. 

2.  The  longus  capitis  (O.T.  rectus  capitis  anticus  major). 

3.  The  rectus  capitis  anterior  (O.T.  anticus  minor). 

Musculus  Longus  Colli. — This  is  the  most  pow^erful  of  the  prevertebral 
muscles,  and  it  lies  nearest  to  the  median  plane.  Its  connections  are  some- 
what intricate,  but  when  it  has  been  thoroughly  cleaned  it  will  be  seen  to 
consist  of  three  portions — viz.,  upper  and  lower  oblique  parts,  and  an 
intermediate  vertical  part. 

The  lower  oblique  division  arises  from  the  lateral  aspect  of  the  bodies  of 


352 


HEAD  AND  NECK 


the  upper  two  or  three  thoracic  vertebrae.  It  extends  upwards,  and  slightly 
laterally,  and  ends  in  two  tendinous  slips  which  are  inserted  into  the  anterior 
tubercles  of  the  transverse  processes  of  the  fifth  and  sixth  cervical  vertebrae. 
In  the  interval  between  this  portion  of  the  longus  colli  and  the  scalenus 
anterior,  the  vertebral  artery  will  be  seen.     The  upper  oblique  part  arises  by 


Rectus  capitus 
anterior 


Rectus  lateralis 

Rectis  capitis 
anterior 


Longus  capitis 


Scalenus 
posterior 


Lona:us  colli 


enus  anterior 
enus  medius 

enus  posterior 


Fig.  140. — Prevertebral  Muscles  of  the  Neck.      On  the  right  side  the  longus 
capitis  has  been  removed.      (Paterson. ) 


three  tendinous  slips  from  the  anterior  tubercles  of  the  transverse  processes 
of  the  third,  fourth,  and  fifth  cervical  vertebrae  ;  it  tapers  somewhat  as  it 
proceeds  upwards  and  medially  to  obtain  a  pointed  ancl  tendinous  insertion 
into  the  anterior  tubercle  of  the  atlas.  The  vertical  part  of  the  muscle  is 
much  the  largest  of  the  three  divisions.  It  lies  along  the  medial  side  of  the 
oblique  portions,  and  is  intimately  connected  with  both  of  them.  It  arises 
in  common  with  the  inferior  oblique  part  by  two  or  three  slips  from  the 
sides  of  the  bodies  of  the  upper  two  or  three  thoracic  vertebrae  ;    above 


PREVERTEBRAL  REGION  353 

this  it  derives  additional  slips  of  origin  from  the  bodies  of  the  lower  two 
cervical  vertebrae  ;  lastly,  its  lateral  border  is  reinforced  by  slips  from  the 
transverse  processes  of  the  lower  three  or  four  cervical  vertebrae.  It 
stretches  vertically  upwards,  and  is  inserted  upon  the  medial  side  of  the 
upper  oblique  part  of  the  muscle  by  three  tendinous  processes,  which 
obtain  attachment  to  the  bodies  of  the  second,  third,  and  fourth  cervical 
vertebras. 

Longus  Capitis  (O.T.  Rectus  Capitis  Anticus  Major). — The  long  capitis 
is  an  elongated  muscle  which  arises  by  four  tendinous  slips  from  the  anterior 
tubercles  of  the  transverse  processes  of  the  third,  fourth,  fifth,  and  sixth 
cervical  vertebrae.  It  is  inserted  anterior  to  the  foramen  magnum,  upon 
the  under  aspect  of  the  basilar  portion  of  the  occipital  bone.  To  reach 
this  insertion  the  muscle  incHnes  slightly  medially  as  it  ascends  upon  the 
anterior  aspect  of  the  vertebral  column.  It  is  supplied  by  twigs  from  the 
first  loop  of  the  cervical  plexus. 

Rectus  Capitis  Anterior  (O.T.  Anticus  Minor). — This  is  a  small  muscle. 
It  is  partly  concealed  by  the  upper  portion  of  the  longus  capitis,  which 
should  be  detached  from  its  insertion,  and  turned  downwards  so  as  to  bring 
it  fully  into  view.  It  arises  from  the  anterior  aspect  of  the  lateral  mass  of 
the  atlas  and,  proceeding  upwards  and  medially,  is  inserted  into  the  under 
surface  of  the  basilar  portion  of  the  occipital  bone  postero-lateral  to  the 
longus  capitis.  It  is  supplied  by  a  filament  from  the  first  loop  of  the 
cervical  plexus. 

Before  proceeding  farther,  the  dissector  should  again  examine  the 
attachments  of  the  scalene  muscles  {v.  p.  322). 

Musculi  Intertransversarii. — To  obtain  a  proper  display  of  the  inter- 
transverse muscles  it  will  be  necessary  to  remove  the  prevertebral  and 
scalene  muscles.  The  intertransverse  muscles  consist  of  seven  pairs  of 
small  fleshy  slips  on  each  side,  which  connect  the  bifid  extremities  of  the 
cervical  transverse  processes  ;  they  are  the  anterior  and  posterior  inter- 
transverse muscles.  Each  anterior  muscle  is  attached  to  the  anterior 
tubercles  of  two  adjacent  transverse  processes  ;  whilst  the  posterior  extends 
between  the  posterior  tubercles.  The  highest  pair  of  muscular  slips  lies 
between  the  atlas  and  the  epistropheus ;  the  lowest  pair  connects  the 
transverse  process  of  the  seventh  cervical  vertebra  with  the  transverse 
process  of  the  first  thoracic  vertebra. 

Nervi  Cervicales. — The  cervical  spinal  nerves  have  a 
very  definite  relation  to  the  intertransverse  muscles.  The 
anterior  branches  of  the  lower  six  nerves  make  their 
appearance  by  passing  laterally  between  the  two  slips  of  the 
corresponding  muscles.  The  posterior  divisions  of  the  same 
nerves  turn  posteriorly,  medial  to  the  posterior  muscular 
slips. 

The  upper  two  cervical  nerves  emerge  from  the  vertebral 
canal  differently  from  the  others.  They  pass  posteriorly 
over  the  posterior  arch  of  the  atlas  and  the  vertebral  arch  of 
the  epistropheus. 

Dissection. — The  vertebral  artery  as  it  traverses  the  succession  of 
foramina  in  the  transverse  processes  of  the  cervical  vertebra  should  now 
be  exposed.  Remove  the  intertransverse  muscles  as  well  as  the  muscles 
still  attached  to  the  transverse  process  of  the  atlas — viz.,  the  rectus  lateralis, 

VOL.  II — 23 


354 


HEAD  AND  NECK 


the  inferior  oblique,  and  the  superior  oblique.  The  anterior  tubercles  and 
the  costal  portions  of  the  transverse  processes  of  the  third,  fourth,  fifth, 
and  sixth  cervical  vertebrae  should  then  be  snipped  off  with  the  bone  forceps. 

Arteria  Vertebralis. — This  is  an  artery  of  great  importance, 
for,  together  with  its  fellow  of  the  opposite  side  and  the  basilar 
artery,  which  is  formed  by  their  union,  it  supplies  the  hind- 
brain,  the  mid-brain,  and  the  posterior  parts  of  the  cerebral 
hemispheres,  and  it  helps  to  supply  the  spinal  medulla.     It 


Posterior  atlanto 

occipital  membrane' 

Posterior  branch  of 

sub-occipital  nerve 

Great  occipital  nerve 

Vertebral  artery- 
Anterior  branch 
of  spinal  nerves- 


Posterior  arch  of  atlas 
Ligamentum  nuchas 


Posterior  branches  of  spinal 
nerves 


Seventh  cervical  vertebra 


Fig.  141. — Dissection  of  the  Ligamentum  Nuchae  and  of  the  Vertebral 
Artery  in  the  Neck. 

commences  at  the  root  of  the  neck,  as  a  branch  of  the  first 
part  of  the  subclavian  artery,  and  it  runs  upwards,  through  the 
transverse  processes  of  the  cervical  vertebrae,  to  the  base  of 
the  skull.  It  enters  the  skull  through  the  foramen  magnum 
and  unites  in  the  posterior  fossa  of  the  cranium,  at  the  lower 
border  of  the  pons,  with  its  fellow  of  the  opposite  side  to 
form  the  basilar  artery.  On  account  of  its  varying  relations 
it  is  divided  into  four  parts.  The  first  part,  which  extends 
from  the  subclavian  artery  to  the  transverse  process  of  the 
sixth  cervical  vertebra,  has  been  seen  already  (p.  251).  It  lies 
between    the    longus    colli    medially,    the    scalenus    anterior 


PREVERTEBRAL  REGION  355 

laterally,  the  transverse  process  of  the  seventh  cervical 
vertebra  and  the  inferior  cervical  ganglion  of  the  sympathetic 
posteriorly,  and  the  vertebral  vein  and  the  common  carotid 
artery  anteriorly. 

The  second  part,  now  exposed,  commences  where  the 
artery  enters  the  transverse  process  of  the  sixth  cervical 
vertebra.  It  passes  vertically  upwards,  through  the  series 
of  foramina  transversaria,  till  it  reaches  the  foramen  in  the 
transverse  process  of  the  epistropheus.  In  that  it  runs 
laterally  as  well  as  upwards  to  gain  the  foramen  in  the 
more  laterally  placed  transverse  process  of  the  atlas ;  and,  as 
it  emerges  upon  the  upper  aspect  of  the  atlas,  the  third 
part  commences  and  curves  round  the  lateral  and  posterior 
aspects  of  the  upper  articular  process  of  that  bone,  in  a 
groove  upon  the  upper  surface  of  the  posterior  arch.  As 
soon  as  it  has  passed  under  cover  of  the  lateral  margin  of  the 
posterior  atlanto-occipital  membrane  it  becomes  the  fourth 
part.  The  fourth  part  turns  upwards,  pierces  the  dura  mater 
and  passes  into  the  skull  through  the  foramen  magnum, 
anterior  to  the  uppermost  digitation  of  the  ligamentum  denti- 
culatum ;  then,  turning  antero-medially,  between  the  hypo- 
glossal nerve  above  and  the  first  cervical  nerve  below,  it 
passes  to  the  anterior  surface  of  the  medulla  oblongata,  and, 
as  already  stated,  joins  its  fellow  of  the  opposite  side  at  the 
lower  border  of  the  pons. 

Relations. — The  relations  of  the  first  part  have  already 
been  sufficiently  considered.  The  second  part  lies  in  and 
between  the  transverse  processes  of  the  cervical  vertebra, 
medial  to  the  intertransverse  muscles,  lateral  to  the  bodies 
of  the  vertebrae,  and  anterior  to  the  anterior  branches  of  the 
cervical  nerves  as  they  pass  laterally.  It  is  surrounded  not 
only  by  the  sympathetic  nerve  plexus  derived  from  the 
inferior  cervical  ganglion,  which  accompanies  all  parts  of 
the  artery,  but  also  by  a  venous  plexus  which  terminates  below 
in  the  vertebral  vein  or  veins.  The  third  part  of  the  artery 
lies  on  the  posterior  arch  of  the  atlas  in  the  anterior  boundary 
of  the  sub-occipital  triangle.  As  it  turns  posteriorly  from  the 
foramen  in  the  transverse  process  of  the  atlas  the  anterior 
branch  of  the  first  cervical  nerve  lies  to  its  medial  side, 
between  it  and  the  lateral  mass  of  that  bone ;  and,  as  it  turns 
medially,  posterior  to  the  upper  articular  facet,  the  trunk  of 
the  first  cervical  nerve  lies  below  it  on  the  posterior  arch,  and 

11—23  a 


356  HEAD  AND  NECK 

the  posterior  branch  enters  the  triangle  from  beneath  its 
lower  border.  For  the  relations  of  the  fourth  part  see  above 
and  p.  443. 

Branches. — No  branch  of  importance  is  given  off  from 
the  first  part.  The  second  part  gives  off  lateral  spinal 
(p.  193)  and  muscular  branches.  The  branches  from  the 
third  part  are  muscular  twigs,  and  branches  to  anastomose 
with  twigs  from  the  occipital  and  the  deep  cervical  arteries. 
The  fourth  part  gives  off  a  meningeal  branch  before  it 
perforates  the  dura  mater  and,  afterwards,  a  series  of  branches 
to  the  central  nervous  system  (see  pp.  443,  444). 

Vena  Vertebralis. — Only  the  first  part  of  the  vertebral 
artery  is  accompanied  by  a  definite  vertebral  vein.  There 
are  no  accompanying  veins  with  the  fourth  part  of  the  artery, 
but  a  plexus  is  formed  round  the  commencement  of  the 
third  part,  by  the  union  of  tributaries  from  the  venous  plexus 
in  the  vertebral  canal  and  from  the  plexus  of  veins  in  the 
sub-occipital  triangle.  This  plexus  accompanies  the  second 
part  of  the  artery  through  the  transverse  processes  of  the 
cervical  vertebrae ;  it  anastomoses  with  the  venous  plexuses  in 
the  vertebral  canal ;  and  it  terminates  below  in  one  or  two 
vertebral  veins ;  these  accompany  the  first  part  of  the  artery 
and  end  in  the  posterior  aspect  of  the  commencement  of  the 
innominate  vein. 

Dissection. — The  muscles  must  now  be  completely  removed,  in  order 
that  the  vertebral  and  cranio-vertebral  joints,  and  the  ligaments  in  con- 
nection with  the  cervical  portion  of  the  vertebral  column  may  be  examined. 


The  Joints  of  the  Neck. 

The  epistropheus,  atlas,  and  occipital  bone  present  a  series 
of  articulations  in  which  the  uniting  apparatus  is  very  different 
from  that  of  the  vertebrae  below. 

Articulations  of  the  Lower  Five  Cervical  Vertebrse. — The 
lower  five  cervical  vertebrae  are  united  together  very  much 
upon  the  same  plan  as  the  vertebrae  in  other  regions  of  the 
vertebral  column.  Both  the  bodies  and  the  vertebral  arches 
are  connected  by  distinct  articulations  and  special  ligaments. 

Three  separate  joints  may  be  said  to  exist  between  the 
opposed  surfaces  of  the  bodies  of  two  adjacent  cervical 
vertebrae — viz.,  a  central  synchondrosis  and  two  small  lateral 
diarthrodial  joints. 


JOINTS  OF  THE  NECK 


357 


The  synchondrosis  occupies  by  far  the  greatest  part  of 
the  interval  between  the  vertebral  bodies,  and  it  presents 
the  usual  characters  of  such  an  articulation.  The  opposed 
bony  surfaces  are  coated  with  a  thin  layer  of  hyaline  or 
encrusting  cartilage,  and  are  brought  into  direct  union 
by  an  interposed  disc  of  fibro-cartilage.  The  intervertebral 
fibro-cartilages  are  distinctly  deeper  anteriorly  than  posteriorly, 
and  upon  this  circumstance  the  cervical  curvature  of  the 
column  in  great  measure  depends. 

The  two  diarthrodial  joints  are  placed  one  on  each  side 
where  the  disc  of  fibro-cartilage  is  absent.  They  are  of  small 
extent,  and  are  confined  entirely  to  the  intervals  between  the 
projecting   lateral    lips    of  the    upper    surface    of    the    body 


Synovial  part  of 
joint  between  bodies 
of  vertebrae 


Joint  between 
articular  processes 


Capsule  around 
joint  between  two 
articular  processes 


Intervertebral  fibro- 
cartilage 


Fig.  142. — Frontal  section  through  bodies  of  certain  of  the 
Cervical  Vertebras. 

and  the  bevelled-off  lateral  margins  of  the  lower  surface  of 
the  vertebral  body  immediately  above.  The  bony  surfaces 
are  coated  with  encrusting  cartilage,  and  are  separated  by 
a  synovial  cavity  protected  by  a  feeble  capsular  ligament. 

The  ligaments  which  bind  the  bodies  of  the  lower  five 
cervical  vertebrae  together  are  the  direct  continuation  upwards 
of  the  anterior  and  the  posterior  longitudinal  ligaments  of 
the  vertebrae.  When  the  medulla  spinalis  was  removed, 
the  laminae  of  the  vertebrae,  below  the  epistropheus,  were 
taken  away  so  that  very  little  dissection  will  be  required  to 
make  out  the  connections  of  both  of  these  ligaments.  The 
anterior  longitudinal  liga7nent  is  a  strong  band  placed  on  the 
anterior  faces  of  the  vertebral  bodies.  It  is  more  firmly  fixed 
to  the  intervening  intervertebral  fibro-cartilages  than  to  the 
bones.      The  posterior   longitudinal  ligament^    which    lies    on 


358  HEAD  AND  NECK 

the  posterior  aspects  of  the  vertebral  bodies,  constitutes  the 
anterior  boundary  of  the  vertebral  canal.  In  the  cervical 
region  it  completely  covers  the  bodies  and  does  not  present 
the  denticulated  appearance  which  is  so  characteristic  lower 
down.  It  is  attached  chiefly  to  the  fibro-cartilages  and 
the  adjacent  margins  of  the  bones. 

The  vertebral  arches  of  the  lower  five  cervical  vertebrae  are 
bound  together  by  {a)  the  articulations  between  the  articular 
processes ;  {b)  ligamenta  flava ;  ic)  interspinous  ligaments ; 
and  {d)  intertransverse  ligaments ;  (e)  ligamentum  nuchae. 

^\i<^  joints  between  the  opposing  articular  processes  are  of 
the  diarthrodial  variety.  The  surfaces  of  bone  are  coated 
with  cartilage ;  there  is  a  joint  cavity  surrounded  by  a 
distinct  capsular  ligament  lined  with  a  stratum  synoviale. 
This  ligament  is  more  laxly  arranged  in  the  neck  than  in 
the  lower  regions  of  the  vertebral  column. 

The  ligamenta  fiava  may  be  examined  on  the  laminae  which  were 
removed  for  the  display  of  the  spinal  medulla,  and  which  the  dissector  was 
directed  to  retain.  They  fill  up  the  gaps  between  the  laminae  of  the 
vertebrae,  and  can  be  best  seen  when  the  anterior  aspect  of  the  specimen 
is  viewed. 

Ligamenta  Flava. — These  ligaments  are  composed  of  yellow 
elastic  tissue.  Each  is  attached  superiorly  to  the  anterior 
surface  and  inferior  margin  of  the  lamina  of  the  vertebra 
above,  whilst  inferiorly  it  is  fixed  to  the  posterior  surface 
and  superior  margin  of  the  lamina  of  the  vertebra  next 
below.  In  this  way  they  form  with  the  laminae  a  smooth, 
even,  posterior  wall  for  the  vertebral  canal.  Each  ligament 
extends  from  the  posterior  part  of  the  articular  processes  to 
the  median  plane,  where  its  free  thickened  median  border  is 
in  contact  with  its  fellow  of  the  opposite  side.  The  median 
slit  between  them,  in  the  space  between  each  pair  of 
vertebral  arches,  is  filled  with  some  lax  connective  tissue, 
which  allows  the  egress  from  the  vertebral  canal  of  some 
small  veins.  The  width  of  the  ligaments  in  the  diiferent 
regions  of  the  vertebral  column  depends  upon  the  size  of 
the  vertebral  canal.  Therefore  they  are  widest  in  the  neck 
and  in  the  lumbar  part  of  the  column.  The  ligamenta  flava, 
by  virtue  of  their  great  strength  and  elasticity,  are  powerful 
agents  in  maintaining  the  curvatures  of  the  vertebral  column ; 
they  also  give  valuable  aid   to  the  muscles  in  restoring  the 


JOINTS  OF  THE  NECK 


359 


vertebral  column  to  its  original  position  after  it  has  been  bent 
in  a  ventral  direction. 

The  interspinous  ligaments  are  most  strongly  developed  in 
the  lumbar  region,  where  they  fill  up  the  intervals  between 
the  adjacent  margins  of  contiguous  spinous  processes.  In 
the  thoracic  region,  and  more  so  in  the  neck,  they  are  very 
weak. 

The  supraspinous  ligaments  are  thickened  bands  which 
connect  the  summits  of  the  spinous  processes.  In  the  neck 
they  are  replaced  by  the  ligamentum  nuchae  (p.  172). 


Pedicle  of 
vertebra  divided 


litliik.. 

Fig.  143. — The  Ligamenta  Flava  in  the  Lumbar  Region  of  the  Spine. 

The  intertransverse  liga??ients  are  feebly  marked  in  the 
cervical  region  and  extend  chiefly  between  the  anterior  bars 
of  the  transverse  processes. 

Articulations  of  the  Epistropheus,  Atlas,  and  Occipital 
Bone.  —  The  articulations  which  exist  between  these  three 
bones  all  belong  to  the  diarthrodial  class.  Between  the  atlas 
and  epistropheus  (O.T.  axis)  there  are  three  such  joints — 
viz.,  a  pair  between  the  opposed  articular  processes,  and  a 
third  between  the  anterior  face  of  the  dens  and  the  posterior 
face  of  the  anterior  arch  of  the  atlas.  Between  the  atlas 
and  occipital  bone  there  is  a  pair  of  joints — viz.,  between 
the  occipital  condyles  and  the  elliptical  cavities  upon  the 
upper  aspects  of  the  lateral  masses  of  the  atlas. 


366  HEAD  AND  NECK 

The  ligaments  connecting  these  three  bones  together  may 
be  divided  into  three  main  groups,  as  follows : — 


Ligaments    connecting    atlas 
with  epistropheus,   . 


Ligaments   connecting   occi- 


"  Anterior  longitudinal. 
Ligamenta  flava. 
Capsular. 
Transverse    portion    of    cruciate    ligament 

with  inferior  crus. 
Accessory   ligaments   of  the    atlanto  -  epis- 
tropheal  joints. 
'  Anterior  longitudinal  ligament. 
Anterior  occipito-atlantal  membrane. 

I  Posterior  occipito-atlantal  membrane. 
Transverse  part  of  cruciate  ligament  with 
superior  crus. 
Capsular. 

{Membrana  tectoria. 
Superior  and  inferior  crura  of  the  cruciate 
ligament. 
Alar. 
Apical. 

Anterior  Longitudinal  Ligament  (Fig.  144). — This  is  a 
continuation  upwards  of  the  common  anterior  longitudinal 
ligament.  Below,  it  is  attached  to  the  anterior  aspect  of 
the  body  of  the  epistropheus,  whilst  above,  it  is  fixed  to  the 
anterior  arch  of  the  atlas.  It  is  thick  and  strong  in  the 
middle,  but  thins  off  towards  the  sides. 

Ligamenta  Flava. — These  fill  the  interval  between  the 
laminae  of  the  epistropheus  and  the  posterior  arch  of  the 
atlas,  to  the  contiguous  margins  of  which  they  are  attached. 
They  are  broader  and  more  membranous  than  the  ligamenta 
flava  at  lower  levels. 

Capsulse  Articulares. — These  are  somewhat  lax,  and  are 
attached  to  the  margins  of  the  articular  processes. 

Membrana  Atlanto-Occipitalis  Anterior  (Fig.  144). — This 
membrane  extends  from  the  upper  border  of  the  anterior  arch 
of  the  atlas  to  the  under  surface  of  the  basilar  portion  of  the 
occipital  bone,  anterior  to  the  foramen  magnum.  On  each 
side  of  the  median  plane  it  is  thin  and  membranous,  and 
stretches  laterally  so  as  to  abut  against  the  atlanto-occipital 
capsular  ligament.  In  the  median  plane  it  is  strengthened 
by  the  upper  part  of  the  anterior  longitudinal  ligament. 

Membrana  Atlanto-Occipitalis  Posterior. — This  is  a  thin  and 
weak  membrane  which  occupies  the  gap  between  the  posterior 
arch  of  the  atlas  and  the  posterior  border  of  the  foramen 
magnum,  to  both  of  which  it  is  attached.     It  is  very  firmly 


JOINTS  OF  THE  NECK 


361 


connected  with  the  dura  mater,  and  on  each  side  it  reaches 
the  atlanto-occipital  capsular  ligament.  Each  of  its  lateral 
borders  forms  an  arch  over  the  groove,  posterior  to  the  upper 
articular  facet  of  the  atlas,  in  which  the  vertebral  artery  and 
the  first  cervical  nerve  are  lodged.  It  is  not  uncommon  to 
find  these  fibrous  arches  ossified. 

Atlanto- Occipital    Capsular   Ligaments.— These  connect 
the  occipital  condyles  with  the  lateral  masses  of  the  atlas. 


Dura  mater 

Vertebral  artery  and 
first  cervical  nerve 


Basilar  portion  of 
occipital  bone 


Anterior  atlanto- 
occipital  membrane 
Two  parts  of  the  apical 
ligament 

Crus  superius 


Anterior  arch  of  atlas 


Transverse  ligament 
Anterior  longitudinal 
ligament 
Crus  inferius 

Lenticular  disc  of  cartilage_ 
between  the  body  of  the  epis- 
tropheus and  the  dens 


Fig.  144.— Median  section  through  the  Basilar  Portion  of  Occipital  Bone, 
the  Atlas,  and  the  Epistropheus.      (From  Luschka,  sHghtly  modified.) 

Between  the  membrana  tectoria  and  the  transverse  ligament  a  small  synovial  bursa 
may  be  seen. 

They  completely  surround  the  joints,  and  are  connected 
anteriorly  with  the  anterior  atlanto-occipital  membrane,  and 
posteriorly  with  the  posterior  atlanto-occipital  membrane. 

The  occipital  bone,  therefore,  around  the  foramen  magnum 
is  attached  by  special  ligaments  to  each  of  the  four  portions 
of  the  atlas — viz.,  to  the  anterior  arch,  to  the  two  lateral 
masses,  and  to  the  posterior  arch. 

Dissection.— Tht  remaining  ligaments  are  placed  within  the  vertebral 
canal  in  connection  with  its  anterior  wall.      For  their  proper  display  it 


362  HEAD  AND  NECK 

is  necessary  therefore  to  remove,  with  the  bone  forceps,  the  laminae  of  the 
epistropheus  and  the  posterior  arch  of  the  atlas.  The  squamous  part  of 
the  occipital  bone  also  must  be  taken  away  by  sawing  it  through,  on 
each  side,  immediately  posterior  to  the  jugular  process  and  the  condyle, 
carrying  the  saw  cut  into  the  foramen  magnum.  The  upper  part  of  the 
tube  of  dura  mater,  which  still  remains  in  the  vertebral  canal,  must 
next  be  carefully  detached.  A  broad  membranous  band  stretching  upwards 
over  the  posterior  aspect  of  the  body  and  dens  of  the  epistropheus 
is  displayed.     This  is  the  membrana  tectoria. 

The  Membrana  Tectoria  (O.T.  Posterior  Occipito- axial 
Ligament). — This  is  a  broad  ligamentous  sheet  which  is 
attached  below  to  the  posterior  aspect  of  the  body  of 
the  epistropheus,  where  it  is  continuous  with  the  posterior 
longitudinal  ligament  of  the  vertebrae.  It  extends  upwards, 
covering  the  dens  and  the  anterior  margin  of  the  foramen 
magnum,  and  is  attached  above  to  the  superior  grooved 
surface  of  the  basilar  portion  of  the  occipital  bone. 

Dissection. — Detach  this  membrane  from  the  epistropheus  and  throw 
it  upwards  upon  the  basilar  portion  of  the  occipital  bone.  By  this  pro- 
ceeding the  accessory  ligaments  of  the  atlanto-epistropheal  joints  and  the 
cruciate  ligament  are  brought  into  view,  and  very  little  further  dissection 
is  required  to  define  them. 

Accessory  Atlanto-epistropheal  Ligaments  (Fig.  145). — 
These  are  two  strong  bands  which  take  origin  from  the 
posterior  aspect  of  the  body  of  the  epistropheus  close  to  the 
base  of  the  dens.  Each  band  passes  upwards  and  laterally, 
and  is  attached  to  the  medial  and  posterior  part  of  the 
lateral  mass  of  the  atlas.  To  a  certain  extent  they  assist  the 
alar  ligaments  in  limiting  the  rotary  movements  of  the  atlas 
upon  the  epistropheus. 

Ligamentum  Cruciatum  (Fig.  145). — The  cruciate  ligament 
is  composed  of  a  transverse  and  a  vertical  part.  The  liga- 
mentum transversum  atlantis  is  by  far  the  most  important  con- 
stituent of  this  apparatus.  It  is  a  strong  band  which  stretches 
from  the  tubercle  on  the  medial  aspect  of  the  lateral  mass  of 
the  atlas  on  one  side  to  the  corresponding  tubercle  on  the 
opposite  side.  With  the  anterior  arch  of  the  atlas  it  forms 
a  ring  which  encloses  the  dens — the  pivot  around  which  the 
atlas  bearing  the  head  turns.  It  is  separated  from  the 
posterior  aspect  of  the  dens  by  a  loose  synovial  membrane 
which  extends  anteriorly  on  each  side  until  it  almost  reaches 
the  synovial  membrane  in  connection  with  the  median  joint 
between  the  dens  and  the  anterior  arch  of  the  atlas.     Indeed, 


JOINTS  OF  THE  NECK 


3^3 


in  some  cases  a  communication  exists  between  the  two  synovial 
cavities. 

The  vertical  part  of  the  cruciate  Hgament  consists  of  an 
upper  and  a  lower  limb,  which  are  termed  the  crura.  Both 
are  attached  to  the  dorsal  surface  of  the  transverse  ligament. 
The  crus  siiperius  is  the  longer  and  flatter  of  the  two,  and 
extends  upwards  on  the  posterior  aspect  of  the  dens  to  be 
attached  to  the  upper  aspect  of  the  basilar  part  of  the 
occipital   bone  immediately  beyond  the   anterior   margin   of 

Membrana  tectoria 
Crus  superius 


Occipi 
bone 


Lateral 

mass  of 

atlas 

Atlanto- 
Epistropheal  joint 

Body  of  Epistro- 
pheus 


Apical 
ligament 


Alar 
ligament 

Crus 
superius 
Transverse 
ligament 


A.  Accessory  atlanto- 
"epistropheal 
ligament 

Crus  inferius 


Membrana  tectoria 


Fig.  145. — Dissection  showing  the  posterior  aspects  of  the  Ligaments  con- 
necting the  Occipital  Bone,  the  Atlas,  and  the  Epistropheus  with  each 
other. 


the  foramen  magnum.  The  crus  inferius^  much  shorter, 
extends  downwards,  and  is  fixed  to  the  posterior  aspect  of 
the  body  of  the  epistropheus. 

Dissection. — Detach  the  superior  crus  from  the  occipital  bone,  and 
throw  it  downwards.  The  apical  ligament  is  thus  displayed,  and  a  better 
view  of  the  alar  ligaments  is  obtained. 

Ligamentum  Apicis  Dentis. — The  apical  ligament  of  the 
dens  consists  of  two  parts — an  anterior  and  a  posterior.  The 
posterior  part  is  a  rounded  cord-like  ligament  which  is  attached 
below  to  the  summit  of  the  dens,  and  above  to  the  anterior 
margin  of  the  foramen  magnum.      This  ligament,  inasmuch 


364  HEAD  AND  NECK 

as  it  is  developed  around  the  continuation  of  the  chorda 
dorsalis  from  the  dens  to  the  basis  cranii,  is  a  structure  of 
considerable  morphological  interest.  The  anterior  part  of 
the  apical  ligament  is  a  flat  and  weak  band  which  is 
attached  above  to  the  anterior  margin  of  the  foramen  magnum 
at  the  same  point  as  the  posterior  portion.  Below,  the  two 
portions  are  separated  by  an  interval  filled  with  cellular  tissue, 
and  the  anterior  part  is  attached  to  the  dens  immediately 
above  its  articular  facet  for  the  anterior  arch  of  the  atlas, 

Ligamenta  Alaria  (Fig.  145). — These  are  very  powerful 
bands  which  spring,  one  from  each  side  of  the  summit  of 
the  dens.  They  pass  laterally  and  slightly  upwards  to  be 
attached  to  the  medial  aspect  of  the  condyloid  eminences  of 
the  occipital  bone.  They  limit  rotation  of  the  head,  and 
in  this  they  are  aided  by  the  accessory  atlanto-epistropheal 
ligaments. 

Movements. — Nodding  movements  of  the  head  are  permitted  at  the 
atlanto -occipital  articulations.  Rotatory  movements  of  the  head  and  atlas 
around  the  dens,  which  acts  as  a  pivot,  take  place  at  ,  the  atlanto- 
epistropheal  joints.     Excessive  rotation  is  checked  by  the  alar  ligaments. 


MOUTH  AND  PHARYNX. 

The  dissectors  must  now  return  to  the  anterior  part  of  the 
skull,  which  had  been  laid  aside  while  the  dissection  of  the 
prevertebral  region  was  being  carried  on.  The  mouth  and 
pharynx  should  engage  their  attention  in  the  first  instance. 

Mouth. — The  mouth  is  the  expanded  upper  part  of  the 
alimentary  canal  which  is  placed  in  the  lower  part  of  the 
face,  below  the  nasal  chambers.  Its  cavity  is  controlled  by 
muscles  which  are  under  the  influence  of  the  will,,  and  it 
is  separable  into  two  parts :  a  smafler  external  part,  termed 
the  vestibule^  which  is  bounded  externally  by  the  lips  and 
cheeks,  and  internally  by  the  teeth  and  gums;  and  a  large 
part,  the  mouth  proper^  which  is  placed  within  the  teeth. 

The  mucous  lining  of  the  mouth  should  be  thoroughly  cleansed,  and 
the  two  subdivisions  of  the  cavity  examined  through  the  oral  fissure. 

Vestibulum  Oris. — The  vestibule  of  the  mouth,  which 
passes  round  the  teeth  and  gums,  is  a  mere  fissure-like  space, 
except  when  the  cheeks  are  inflated  with  air.  It  is  into  this 
part  of  the   mouth   that   the   parotid   ducts   open  (p.    261). 


MOUTH  365 

Above  and  below,  it  is  bounded  by  the  reflection  of  the 
mucous  membrane  from  the  lips  and  cheeks  on  to  the 
alveolar  margins  of  the  maxilla  and  mandible.  Anteriorly, 
it  opens  upon  the  face  by  means  of  the  oral  fissure ;  whilst 
posteriorly,  it  communicates,  on  each  side,  with  the  cavity 
of  the  mouth  proper  through  the  interval  between  the  last 
molar  tooth  and  the  anterior  border  of  the  ramus  of  the 
mandible.  The  existence  of  this  communication  is  of  import- 
ance in  cases  of  spasmodic  closure  of  the  jaws  when  all  the 
teeth  are  in  place,  because  through  it  fluids  may  be  introduced 
into  the  posterior  part  of  the  mouth  proper. 

In  paralysis  of  the  facial  muscles  the  lips  and  cheeks  fall  away  from  the 
dental  arches  and  food  is  apt  to  lodge  in  the  vestibule. 

Cavum  Oris  Proprium.— The  mouth  proper  is  bounded 
anteriorly  and  laterally  by  the  gums  and  teeth,  whilst  posteriorly 
it  communicates  by  means  of  the  isthmus  faudu?n  with  the 
pharynx.  The  floor  is  formed  by  the  tongue  and  the  mucous 
membrane  which  connects  it  with  the  inner  aspect  of  the 
mandible ;  the  roof  is  vaulted,  and  is  formed  by  the  hard 
and  the  soft  palates.  Into  this  part  of  the  buccal  cavity  the 
ducts  of  the  submaxillary  glands  and  the  ducts  of  the  sub- 
lingual glands  open  (p.  288).  When  the  mouth  is  closed 
the  dorsum  of  the  tongue  is  usually  applied  more  or  less 
closely   to  the   palate   and   the  cavity   is    almost   completely 

obliterated. 

The  various  parts  which  bound  the  oral  cavity  may  now 

be  examined  in  turn. 

Labia  Oris.— The  structure  of  the  lips  has  m  a  great 
measure  been  examined  already  in  the  dissection  of  the  face 
(p  133).  Each  lip  is  composed  of  four  layers:  (i)  Cuta- 
neous; (2)  muscular;  (3)  glandular;  and  (4)  mucous.  The 
skin  and  mucous  membrane  become  continuous  wath  each 
other  at  the  free  margin  of  the  lip.  From  the  inner  aspect 
of  the  upper  lip  the  mucous  membrane  is  reflected  to  the 
alveolar  margin  of  the  maxilla  and  from  the  inner  aspect  of  the 
lower  lip  to  the  mandible.  In  each  case  it  is  raised  m  the 
median  plane  in  the  form  of  a  free  fold  termed  the  frenulum. 
The  muscular  layer  constitutes  the  chief  bulk  of  the  lips.  It 
is  formed  by  the  orbicularis  oris  and  the  various  muscles 
which  converge  upon  the  oral  fissure.  Numerous  labial 
<rlands  lie  in  the  submucous  tissue  which  intervenes  between 


366 


HEAD  AND  NECK 


the  mucous  membrane  and  the  muscular  fibres.  The  ducts 
of  these  glands  pierce  the  mucous  membrane  and  open  into 
the  vestibule.  In  each  lip  there  is  an  arterial  arch  formed 
by  the  corresponding  labial  arteries  (p.  130). 

The  lymph  vessels  of  both  lips  join  the  submaxillary 
lymph  glands,  but  some  of  the  lymph  vessels  of  the  upper 
lip  pass  to  the  superficial  parotid  glands. 

Buccae. — Six  layers  enter  into  the  construction  of  the 
cheeks,  all  of  which  have  been  examined  in  the   dissection 


Tip  of  tongue 
turned  up 


Deep  lingual  vein 


Orifice  of 
submaxillary  duct 


Frenulum  linguae 
Plica  fimbriata 

'Plica  sublinguali 


Fig.  146. — The  Sublingual  Region  in  the  Interior  of  the  Mouth. 

of  the  face,  (i)  Skin  ;  (2)  a  fatty  layer  traversed  by  some  of 
the  facial  muscles  and  the  external  maxillary  artery;  (3) 
the  bucco-pharyngeal  aponeurosis;  (4)  the  buccinator  muscle; 
(5)  numerous  buccal  glands^  similar  in  character  to  the  labial 
glands,  lie  in  the  submucous  tissue  between  the  mucous  mem- 
brane and  the  buccinator  muscle  ;  (6)  the  mucous  membrane. 
Four  or  five  mucous  glands  of  larger  size,  termed  the  molar 
glands^  occupy  a  more  superficial  position.  They  lie  either 
external  or  internal  to  the  bucco-pharyngeal  aponeurosis,  close 
to  the  point  where  this  is  pierced  by  the  parotid  duct,  and 
their  ducts  open  into  the  vestibule  of  the  mouth.  The 
bucco-pharyngeal  aponeurosis  is  a  dense  fascia  which  covers  the 
buccinator  muscle.      Above   and  below,    it    is    attached    to 


MOUTH 


367 


the  alveolar  portions  of  the  maxilla  and  mandible,  whilst 
posteriorly  it  is  continued  over  the  pharynx.  The  musctes 
which  traverse  the  fatty  laye?-  are  chiefly  the  zygomaticus, 
the  risorius,  and  the  posterior  fibres  of  the  platysma.  The 
parotid  duct  pierces  the  inner  three  layers  of  the  cheek,  and 
opens  into  the  vestibule  of  the  mouth  opposite  the  second 
molar  tooth  of  the  maxilla. 

Gingivae  et  Dentes. — The  mucous  membrane  of  the  gums 
is  smooth,  vascular,  and  firmly  bound  down  to  the  subjacent 


^f«»»nT^^^ 


Uvula 


Pharyngo- 
palatine  arch 

Tonsil 

Glosso-palatine 

arch 

Posterior  wall  of 

oral  pharynx 


Tongue 


Fig.  147.— Isthmus  of  the  Fauces  as  seen  through  the  widely  opened  Mouth. 
The  tonsils  in  the  subject  from  which  this  drawing  was  made  were 
somewhat  enlarged. 

periosteum  of  the  alveolar  portions  of  the  jaws  by  a  stratum 
of  dense  connective  tissue.  It  is  continuous  on  the  one 
hand  with  the  mucous  membrane  of  the  lips  and  cheeks, 
and  on  the  other  with  the  mucous  membrane  of  the  mouth 
proper.     The  gums  closely  embrace  the  necks  of  the  teeth. 

In  the  adult  the  teeth  in  each  jaw  number  sixteen.  From 
the  median  line  posteriorly,  on  each  side,  they  are  the  two 
incisors,  the  canine,  the  two  premolars,  the  three  molars. 

Floor  of  the  Mouth. — The  mucous  membrane  is  reflected 
from  the  inner  aspect  of  the  mandible  to  the  side  of  the 
tongue,  but  in  the  anterior  part  of  the  mouth  the  tongue  lies 


368  HEAD  AND  NECK 

more  or  less  free  in  the  buccal  cavity,  and  there  the  mucous 
membrane  stretches  across  the  floor  from  one  side  of  the 
mandible  to  the  other.  On  each  side  in  this  region  the 
projection  formed  by  the  sublingual  gland,  the  plica  sublingualis^ 
can  be  distinguished.  Further,  if  the  tongue  is  pulled 
upwards,  a  median  fold  of  mucous  membrane  will  be  seen  to 
connect  its  under  surface  to  the  floor.  This  is  the  frenulum 
linguce.  At  the  sides  of  the  frenulum  the  dissector  must 
look  for  the  openings  of  the  submaxillary  ducts.  Each 
terminates  on  a  papilla  placed  close  to  the  side  of  the 
frenulum.  More  posteriorly,  between  the  side  of  the  tongue 
and  the  mandible  and  on  the  summit  of  the  plica  sub- 
lingualis, are  the  openings  of  the  sublingual  ducts. 

Roof  of  the  Mouth. — The  hard  and  the  soft  palates  form 
the  continuous  concave  and  vaulted  roof  of  the  mouth  (Fig. 
149).  Projecting  from  the  middle  of  the  posterior  free  margin 
of  the  soft  palate,  and  resting  upon  the  dorsum  of  the  tongue, 
the  uvula  will  be  seen  (Fig.  147).  Running  along  the  median 
line  of  both  the  hard  and  the  soft  palates  is  a  raphe 
which  terminates  anteriorly,  opposite  the  incisive  foramen, 
in  a  slight  elevation  or  papilla  termed  the  incisive  papilla. 
In  the  anterior  part  of  the  hard  palate  the  mucous  membrane, 
on  each  side  of  the  raphe,  is  thrown  into  three  or  four 
transverse  hard  corrugations  or  ridges ;  more  posteriorly  it  is 
comparatively  smooth.  By  carefully  palpating  the  postero- 
lateral angles  of  the  palate  the  dissector  will  be  able  to  feel 
the  hamuli  of  the  medial  pterygoid  laminae. 

Isthmus  Faucimn. — This  name  is  given  to  the  communi- 
cation between  the  mouth  proper  and  the  pharynx  (Fig.  147). 
To  obtain  a  good  view  of  it  the  mouth  must  be  well  opened 
and  the  tongue  depressed.  The  isthmus  faucium  and  the 
parts  which  bound  it  can  be  examined  best  in  the  living 
subject  (Fig.  147).  It  is  bounded  above  by  the  soft  palate, 
below  by  the  dorsum  of  the  tongue,  and  on  each  side  by  two 
curved  folds  of  mucous  membrane,  termed  respectively  the 
arcus  glossopalatinus  (O.T.  anterior  pillars  of  the  fauces)  and 
the  arcus  pharyngopalatinus  (O.T.  posterior  pillars  of  the 
fauces). 

The  arcus  palatini  spring  from  the  base  of  the  uvula,  and 
arch  laterally  and  then  downwards.  The  arcus  glossopalatinus 
inclines  anteriorly  as  it  descends ;  it  ends  upon  the  side  of 
the  posterior  part  of  the  tongue,  and  it  encloses  the  glosso- 


PHARYNX  369 

palatinus  muscle.  The  arcus pharyngopalatinus,  more  strongly 
marked,  inclines  posteriorly,  and  is  lost  upon  the  side  of  the 
pharynx ;  it  encloses  the  pharyngo-palatinus  muscle. 

In  the  triangular  interval  which  is  formed  by  the  divergence 
of  these  two  folds  lies  the  tonsil. 

Strictly  speaking,  the  term  isthmus  fauciuni  should  be  confined  to  the 
interval  between  the  two  glosso-palatine  arches,  as  the  tonsil  and  the 
pharyngo-palatine  arches  belong  to  the  lateral  wall  of  the  pharynx. 

Pharynx. — The  pharynx  is  a  wide  musculo-aponeurotic 
canal,  about  5  inches  long,  which  extends  from  the  base  of 
the  cranium  to  the  level  of  the  body  of  the  sixth  cervical 
vertebra.  There,  at  the  lower  border  of  the  cricoid  cartilage, 
it  becomes  continuous  with  the  oesophagus.  Placed  posterior 
to  the  nasal  cavities,  the  mouth  and  the  larynx,  it  serves  as 
the  passage  which  conducts  air  to  and  from  the  larynx,  as  well 
as  the  food  from  the  mouth  to  the  oesophagus. 

Under  ordinary  conditions  it  is  expanded  from  side  to 
side  and  compressed  antero-posteriorly,  so  that  it  possesses 
anterior  and  posterior  walls  and  two  lateral  borders.  Above  the 
level  of  the  orifice  of  the  larynx  there  is  always  sufficient 
space  for  the  passage  of  air  to  the  lungs,  but  below  the 
orifice  of  the  larynx  the  anterior  and  posterior  walls  are  in 
contact,  except  when  separated  by  the  passage  of  food. 

It  is  widest  above,  at  the  base  of  the  cranium,  posterior 
to  the  orifices  of  the  auditory  tubes  (O.T.  Eustachian). 
Thence  it  narrows  to  the  level  of  the  hyoid  bone.  It  widens 
again  at  the  level  of  the  upper  part  of  the  larynx  and  then 
rapidly  narrows  to  its  termination. 

To  obtain  a  proper  idea  of  the  connections  of  the  pharynx,  the  dissector 
should  distend  its  walls  moderately  by  stuffing  it  with  tow.  This  may  be 
introduced  either  from  above,  through  the  mouth,  or  from  below,  through 
the  oesophagus. 

The  pharynx  will  now  present  a  somewhat  ovoid  form. 
Posteriorly,  its  wall  is  complete,  and,  when  in  position,  it  lies 
anterior  to  the  upper  six  cervical  vertebrae,  the  prevertebral 
muscles,  and  the  prevertebral  fascia.  To  these  it  is  bound 
by  some  lax  connective  tissue  which  offers  no  impediment  to 
the  movements  of  the  canal  during  the  process  of  degluti- 
tion. Laterally,  the  pharynx  is  related  to  the  great  vessels 
and  nerves  of  the  neck,  as  well  as  to  the  styloid  process  and 
the  muscles  which  take  origin  from  it.     Upon  this  aspect  of 

VOL.  II — 24 


370  -  HEAD  AND  NECK 

the  pharynx  also  is  placed  the  pharyngeal  plexus  ot  nerves, 
which  supplies  its  walls  with  motor  and  sensory  twigs.  An- 
teriorly, the  pharyngeal  wall  is  interrupted  by  the  openings  of 
the  nasal  cavities,  mouth,  and  larynx ;  and  it  is  from  the 
structures  which  lie  in  proximity  to  these  apertures  that  it 
derives  its  principal  attachments.  Thus  from  above  down- 
wards it  is  attached  on  each  side — (a)  to  the  medial  pterygoid 
lamina ;  (d)  to  the  pterygo-mandibular  raphe;  (c)  to  the  side 
of  the  tongue ;  (d)  to  the  inner  aspect  of  the  mandible ;  {e) 
to  the  hyoid  bone  ;  (/)  to  the  thyreoid  cartilage ;  {g)  to  the 
cricoid  cartilage.  Above,  it  is  attached  to  the  basis  cranii. 
These  various  attachments  will  be  studied  more  fully  when 
the  constituent  parts  of  its  walls  are  dissected. 

It  should  be  noted  that  an  altogether  false  idea  of  the  natural  form  of 
the  pharynx  is  obtained  when  it  is  examined  in  its  present  stuffed  condition, 
and  removed  from  the  vertebral  column.  When  seen  in  transverse  sections 
of  the  frozen  body  it  will  be  noted  that,  with  the  exception  of  its  upper  or 
nasal  part,  which  remains  patent  under  all  conditions,  the  anterior  wall  is 
more  or  less  nearly  approximated  to  the  posterior  wall,  and  below  the 
opening  of  the  larynx  it  presents  the  appearance  of  a  simple  transverse 
slit. 

Pharyngeal  Wall. — The  wall  of  the  pharynx  consists  of 
four  well-marked  strata.  These  are  from  without  inwards : 
(i)  bucco-pharyngeal  fascia;  (2)  pharyngeal  muscles;  (3) 
pharyngeal  aponeurosis ;  (4)  mucous  membrane.  The 
muscular  layer,  which  is  composed  of  the  three  constrictor 
muscles,  with  the  stylo-pharyngeus  and  pharyngo-palatinus 
on  each  side,  must  now  be  dissected. 

For  this  purpose  place  the  preparation  so  that  the  chin  rests  upon  a 
block  and  the  pharynx  hangs  downwards  with  its  posterior  surface 
towards  the  dissector.  The  constrictor  muscles  should  now  be  carefully 
cleaned,  in  the  direction  of  the  muscular  fibres,  by  removing  the  bucco- 
pharyngeal fascia,  which  covers  them. 

Bucco-pharyngeal  Fascia. — This  is  a  coating  of  fibrous 
tissue  which  ensheaths  both  the  buccinator  and  the  pharyn- 
geal muscles. 

Venae  Pharyngese. — Upon  the  posterior  wall  and  lateral 
borders  of  the  pharynx  the  dissector  should  notice  numerous 
veins  joined  together  in  a  plexiform  manner.  These  con- 
stitute the  pharyngeal  venous  plexus,  which  collects  blood 
from  the  pharynx,  soft  palate,  and  prevertebral  region.  It 
communicates  with  the  pterygoid  plexus  and  the  cavernous 
sinus.     Two  or  more  channels  lead  the  blood  from  it  to  the 


PHARYNX 


371 


internal  jugular  vein.  This  venous  plexus,  together  with  the 
pharyngeal  plexus  of  nerves,  will  require  to  be  removed  in 
order  to  display  the  muscles  properly. 

Constrictor  Muscles. — The  constrictor  muscles  are  three 
curved  sheets  of  muscular  fibres  which  are  so  arranged  that 
they   overlap    each    other    from    below    upwards ;    thus,   the 


Buccinator. 
Tensor  veil  palatini. 
Levator  veli  palatini. 
Superior  constrictor. 
Middle  constrictor. 
Inferior  constrictor. 
Thyreo-hyoid. 
Hyoglossus. 
Stylo-hj-oid. 
Mylo-hj-oid. 
,  Crico-thyreoid. 
Stylo-pharjmgeus. 
Stylo-glossus. 
Sti'lo-hyoid  ligament. 
Pter^-go-mandibular  raphe. 
Glosso-phar3-ngeal  nerve. 
Superior  larj-ngeal  artery. 
Superior  lar^-ngeal  nerve. 
External  larj-ngeal  ner\'e. 
Inferior  lar^Tigeal  nerve  and 
arterj'. 


Fig.  148.— Profile  view  of  the  Pharynx  to  show  the  Constrictor 
iSIuscles.      (From  Turner.) 

inferior  constrictor  overlaps  the  lower  part  of  the  middle 
constrictor,  whilst  the  middle  constrictor,  in  turn,  overlaps  the 
lower  part  of  the  superior  constrictor.  The  three  muscles  are 
inserted,  in  the  median  plane,  into  the  median  raphe  which 
descends  from  the  basilar  portion  of  the  occipital  bone  along 
the  posterior  aspect  of  the  pharynx. 

Mtisaclus   Constrictor  Fhary?igis   Inferior  (Fig.    148,  f). — 


372  HEAD  AND  NECK 

The  inferior  constrictor  muscle  is  relatively  short  anteriorly 
at  its  origin,  and  relatively  long  posteriorly,  where  it  blends  with 
the  fellow  of  the  opposite  side  in  the  median  raphe  of  the 
posterior  wall  of  the  pharynx.  It  arises  from  the  posterior 
part  of  the  side  of  the  cricoid  cartilage,  and  from  the 
inferior  cornu,  the  oblique  line,  and  the  upper  border  of 
the  thyreoid  cartilage.  The  muscle  curves  posteriorly  and 
medially  around  the  pharyngeal  wall  to  meet  its  fellow  of 
the  opposite  side  in  the  median  raphe.  The  lower  fibres  take 
a  horizontal  direction,  but  the  remainder  ascend,  with  increas- 
ing degrees  of  obliquity,  until  the  highest  fibres  reach  the  raphe 
at  a  point  a  short  distance  below  the  basis  cranii.  The  lower 
margin  of  the  inferior  constrictor  overlaps  the  commencement 
of  the  oesophagus,  and  the  inferior  laryngeal  nerve  and  the 
laryngeal  branch  of  the  inferior  thyreoid  artery  pass  upwards, 
under  cover  of  it,  to  reach  the  larynx. 

Musculus  Constrictor  Pharyngis  Medius. — This  is  a  fan- 
shaped  muscle  (Fig.  148,  e).  It  arises  from  the  great  and 
small  cornua  of  the  hyoid  bone  and  from  the  lower  part  of 
the  stylo-hyoid  ligament.  From  this  origin  its  fibres  pass 
round  the  pharyngeal  wall,  to  be  inserted  with  the  corre- 
sponding fibres  of  the  opposite  side  into  the  median  raphe. 
As  they  pass  postero- medially,  the  lowest  fibres  descend, 
the  highest  ascend,  and  the  intermediate  fibres  run  horizontally. 
The  lower  portion  of  this  muscle  is  overlapped  by  the 
inferior  constrictor,  and  in  the  interval  which  separates  the 
margins  of  the  muscles  anteriorly,  opposite  the  thyreo-hyoid 
interval,  the  internal  laryngeal  nerve  and  the  laryngeal  branch 
of  the  superior  thyreoid  artery  will  be  seen  piercing  the 
thyreo-hyoid  membrane  to  gain  the  interior  of  the  pharynx. 

Dissection. — The  superior  constrictor  possesses  a  somewhat  complicated 
origin,  and  to  bring  this  fully  into  view  it  will  be  necessary  to  cut  through 
the  internal  pterygoid  muscle  about  its  middle,  if  this  has  not  already  been 
done  (p.  293),  and  turn  the  upper  and  lower  portions  aside. 

Musculus  Constrictor  Pharyngis  Superior  (Fig.  148,  d\ — 
The  superior  constrictor  has  a  weak  but  continuous  line 
of  origin  from  the  following  parts  :  {a)  the  lower  third  of 
the  posterior  border  of  the  medial  pterygoid  lamina  and  its 
hamulus  ;  {f)  the  pterygo-mandibular  raphe,  which  is  common 
to  it  and  the  buccinator  muscle;  {c)  the  posterior  end  of  the 
mylo-hyoid  ridge  on  the  inner  aspect  of  the  mandible ;  {d)  the 
mucous    membrane  of  the  mouth   and   side  of  the   tongue. 


PHARYNX 


373 


From  this  somewhat  extensive  origin,  the  fibres  curve  postero- 
medially  to  reach  the  median  raphe,  whilst,  as  a  rule,  some 
of  the  highest  gain  a  distinct  insertion  into  the  pharyngeal 
tubercle  on  the  under  surface  of  the  basi-occipital  bone. 

The  lower  part  of  the  superior  constrictor  is  overlapped 
by  the  middle  constrictor,  and  the  stylo-pharyngeus  passes  into 
the  interval  between  the  two  as  it  descends  to  its  insertion 
(Fig.  148,  n).  The  upper  border  of  the  muscle,  which  is 
free  and  crescentic,  falls  short  of  the  basis  cranii. 

Raphe  Pterygo-mandibularis  (Fig.  148,  q). — This  is  a 
strong,  narrow,  tendinous  band,  which  extends  from  the 
hamulus  of  the  medial  pterygoid  lamina  to  the  posterior 
part  of  the  mylo-hyoid  ridge  of  the  mandible.  It  acts  as 
a  tendinous  bond  of  union  between  the  buccinator  and 
superior  constrictor  muscles,  and  its  connections  can  be 
appreciated  best  by  introducing  the  finger  into  the  mouth 
and  pressing  laterally  along  the  course  of  the  raphe. 

Sinus  of  Morgagni. — This  name  is  applied  to  the  semi- 
lunar space  which  intervenes  between  the  upper  crescentic 
margin  of  the  superior  constrictor  and  the  basis  cranii. 
The  deficiency  in  the  muscular  wall  of  the  pharynx  in  this 
region  is  compensated  for  by  the  increased  strength  of  the 
pharyngeal  aponeurosis,  which,  in  this  situation,  is  called  the 
pharyngo-basilar  fascia.  In  contact  with  the  outer  surface  of 
the  aponeurosis  are  two  muscles  belonging  to  the  soft  palate 
— viz.  the  levator  veli palatini  and  the  tensor  veli  palatini  (Fig. 
148,  c  and  b\  The  levator,  which  is  rounded  and  fleshy,  lies 
posterior  to  the  tensor,  which  is  flat  and  more  tendinous. 
The  tensor  can  readily  be  recognised  from  its  position  in 
relation  to  the  deep  surface  of  the  internal  pterygoid  muscle 
and  from  its  tendon  turning  medially  under  the  hamulus  of 
the  medial  pterygoid  lamina.  In  the  upper  part  of  the  space, 
close  to  the  basis  cranii  and  between  the  origin  of  the  two 
muscles,  will  be  seen  the  auditory  tube  (O.T.  Eustachian  tube). 

Pharyngeal  Aponeurosis. — The  upper  part  of  the  pharyn- 
geal aponeurosis,  th.Q  phary?igo-basilar  fascia,  is  strong,  and  it 
maintains  the  integrity  of  the  wall  of  the  pharynx  where  the 
muscular  fibres  are  absent.  As  it  is  traced  downwards  it 
gradually  becomes  weaker,  until  it  is  ultimately  lost  as  a 
distinct  layer.  It  lies  between  the  muscles  and  mucous  mem- 
brane and  comes  to  the  surface  only  where  the  muscles  are 
absent.     It  is  the  principal  means  by  which  the  pharynx  is 

II — 24(2 


374 


HEAD  AND  NECK 


attached  to  the  base  of  the  skull,  and  it  is  united  also  to  the 
auditory  tubes  and  the  bony  margins  of  the  choancB. 

Dissectioji. — The  pharynx  should  now  be  opened  by  a  vertical  median 
incision   through   the   entire  length  of  its  posterior  wall.     At    the  upper 


Middle  nasal  concha 

Middle  meatus 

Atrium 


Inferior 
nasal  conchaN 
Inferior  meatus 

Vestibule  of 
nasal  cavity 


Soft  palate 


Glosso- 
palatine  arch 


Superior  meatus 

Recessus  spheno-ethmoidalis 
Sphenoidal  sinus 
Hypophysis 

Pharyngeal  recess 
Pharyngeal  tonsil 

Orifice  of  auditory  tube 

Upper  surface 

of  soft  palate 

Salpingo-pharyngeal 

fold 

Pharyngo-palatine 

arch 

Tonsil 


Pharyngeal  surface 
of  tongue 


Genio-glossus 

Genio-hyoid '^ 
Mylo-hyoid 

Hyoid  bone 
Cartilage  of  epiglottis 


Thyreoid  cartilage 


Fig.  149. — Sagittal  section,  a  little  to  the  right  of  the  median  plane, 
through  the  Nasal  Cavity,  the  Mouth,  Larynx,  and  Pharynx. 

extremity  of  this  cut,  the  knife  should  be  carried  transversely,  close  to  the 
basis  cranii.  The  stuffing  should  be  removed  and  the  mucous  surface  of 
the  pharynx  cleansed. 

Interior  of  the  Pharynx. — The  mucous  me^nbrane  is  now 
exposed,    and    it    should    be    noted    that    it  is    continuous, 


PHARYNX  375 

through  the  various  apertures  which  open  into  the  pharynx, 
with  the  mucous  membrane  of  the  nasal  cavities^  the  auditory 
tubes  and  tympanic  cavities,  the  mouth  proper,  the  larynx,  and 
the  (Esophagus. 

Racemose  glands,  which  He  immediately  subjacent  to  the 
mucous  membrane  and  secrete  mucus,  are  present  in  great 
numbers.  There  are  also  numerous  ly^nph  follicles,  and 
in  certain  localities  these  are  aggregated  together  into  large 
masses  (the  tonsils  and  the  pharyngeal  tonsil).  These  will 
be  studied  with  the  regions  of  the  pharynx  in  which  they 
are  placed. 

The  soft  palate  projects  into  the  pharynx,  posterior  to 
the  isthmus  faucium,  and  divides  the  cavity  of  the  pharynx 
into  an  upper  and  a  lower  part.  The  upper  part,  called 
the  naso  -  pharynx,  communicates  with  the  nasal  cavities 
and  the  tympanic  cavities  by  four  apertures,  viz.  the  two 
choance  (O.T.  posterior  nares)  and  the  two  auditory  tubes 
(O.T.  Eustachian  tubes). 

The  lower  portion  of  the  pharynx  may  be  regarded  as 
consisting  of  an  oral  part,  w^hich  lies  posterior  to  the 
mouth  and  tongue,  and  a  lary?igeal  part,  placed  posterior 
to  the  larynx.  Below  the  soft  palate  there  are  three 
openings  into  the  pharynx,  viz.  the  opening  of  the  mouth  or 
isthnus  faucium,  the  opening  of  the  larynx,  and  the  opening  of 
the  (Esophagus. 

Pars  Nasalis. — The  naso-pharynx  is  situated  immediately 
posterior  to  the  nasal  cavities  and  below  the  body  of  the 
sphenoid  and  the  basilar  part  of  the  occipital  bone.  It  is  the 
widest  part  of  the  pharynx.  Its  walls,  except  the  soft  palate, 
are  not  capable  of  movement,  and,  consequently,  its  cavity 
always  remains  patent,  and  presents  under  all  conditions  very 
much  the  same  form. 

In  its  anterior  boundary  are  the  choan^,  through  which  it 
opens  into  the  nasal  cavities.  The  choance  are  two  oblong 
orifices  which  slope  from  the  base  of  the  cranium  downwards 
and  anteriorly  to  the  posterior  border  of  the  hard  palate. 
Each  is  an  inch  long  and  half  an  inch  wide,  and  it  is  separated 
from  its  fellow  by  the  posterior  part  of  the  septum  nasi,  which 
in  this  region  is  formed  by  the  vomer.  By  looking  through 
the  choanae  a  partial  view  of  the  lower  two  meatuses  of  the 
nose  and  of  the  posterior  ends  of  the  middle  and  inferior 
conchae  may  be  obtained. 
11—24  h 


376  HEAD  AND  NECK 

On  the  lateral  wall  of  the  naso-pharynx,  on  each  side,  is 
seen  the  orifice  of  the  auditory  tube,  and  posterior  to  it  the 
pharyngeal  recess.  The  ostmm  pharyngeiim  of  the  auditory 
tube  lies  immediately  posterior  to  the  lower  part  of  the 
corresponding  choana,  at  a  level  which  corresponds  closely 
with  the  posterior  end  of  the  inferior  concha.  It  is  bounded 
above  and  posteriorly  by  a  prominent  and  rounded  margin 
termed  the  torus  tubarhis,  which  is  altogether  deficient  below 
and  anteriorly.  A  fold  of  mucous  membrane,  termed  the 
salpingo-pharyngeal  fold^  descends  upon  the  lateral  wall  of  the 
pharynx  from  the  posterior  lip  of  the  orifice  of  the  auditory 
tube.     As  this  is  traced  downwards  it  gradually  disappears. 

The  dissector  should  pass  a  Eustachian  catheter  through  the  nose  into 
the  auditory  tube.  Hold  the  catheter  with  the  point  downwards.  Pass  it 
posteriorly  through  the  right  nasal  cavity,  along  the  septum  of  the  nose,  to 
the  posterior  wall  of  the  pharynx.  Pull  it  towards  the  palate  till  the  bent  end 
of  the  catheter  catches  against  the  back  of  the  hard  palate.  Turn  the  point 
through  a  quarter  of  a  circle  to  the  right  side  of  the  head  and  it  will  enter 
the  right  auditory  tube.  If  it  is  desired  to  catheterise  the  left  auditory  tube 
pass  the  catheter  through  the  left  nasal  cavity,  and  in  the  final  stage  turn  the 
point  to  the  left  side. 

In  the  natural  condition  of  parts  there  is  a  deep  recess 
on  the  lateral  wall  of  the  naso-pharynx  immediately  posterior 
to  the  prominent  posterior  lip  of  the  orifice  of  the  auditory 
tube.     This  is  termed  the  lateral  recess  of  the  pharynx. 

The  roof  and  posterior  wall  of  the  naso-pharynx  are  not 
marked  off  from  each  other.  They  form  together  a  continuous 
curved  surface.  The  upper  portion  of  this  surface  looks 
downwards  and  may  be  regarded  as  the  roof;  the  lower  portion, 
which  looks  anteriorly,  constitutes  the  posterior  wall.  The  roof 
is  formed  by  the  basilar  part  of  the  occipital  bone,  and 
also  by  a  small  part  of  the  under  surface  of  the  basi-sphenoid, 
covered  with  a  dense  periosteum  and  a  thick  coating  of  mucous 
membrane.  The  posterior  wall  is  supported  posteriorly  by 
the  anterior  arch  of  the  atlas  and  the  anterior  surface  of  the 
epistropheus.  In  that  part  of  the  roof  which  lies  between  the 
two  lateral  recesses  of  the  naso-pharynx  there  is  a  marked 
collection  of  lymphoid  tissue,  the  pharyngeal  tonsil.  Over  its 
surface  the  mucous  membrane  is  thickened  and  wrinkled,  and 
in  its  lower  part  a  small  median  pit,  termed  the  pharyngeal 
bursa,  may  usually  be  found ;  it  is  just  large  enough  to  admit 
the  point  of  a  fine  probe. 

The  floor  of  the  naso-pharynx  is  formed  by  the  curved, 


PHARYNX 


377 


sloping  upper  surface  of  the  soft  palate.  Between  the  posterior 
border  of  the  soft  palate  and  the  posterior  wall  of  the  pharynx 
there  is  an  interval,  termed  the  pharyngeal  isthmus,  through 
which  the  naso-pharynx  communicates  with  the  oral  pharynx. 

It  is  important  to  note  that  the  posterior  wall  and  roof  of  the  naso- 
pharynx can  be  explored  by  the  finger  introduced  through  the  mouth  and 

the  pharyngeal  isthmus.  ,      , .  ,         n         ■,  r 

When  the  naso-pharynx  is  illuminated,  by  light  reflected  from  a  mirror 


Tongue 


Hyoid 
Plica  vocalis 

Rima  glottidis 

Recessus  piriformis 

Superior  cornu 
of  thyreoid 


Pharyngeal  wall 
(cut) 


Glosso-epiglottic 
fold 


Vallecula 

Pharyngo- 
epiglottic  fold 

Epiglottis 

Tubercle  of 
epiglottis 

Ary-epiglottic 

fold 

Laryngeal  ventricle 

Plica  ventricularis 
Cuneiform  cartilage 

Corniculate 
cartilage 


Posterior  aspect 
of  cricoid  cartilage 


Fig.  150.— Superior  Aperture  of  Larynx  exposed  by  cutting  through 
the  posterior  wall  of  the  pharynx. 

introduced  through  the  mouth,  a  view  of  the  four  orifices  which  open  into 
this  part  of  the  pharynx  may  be  obtained.  Owing  to  the  mirror  being 
placed  obliquely,  and  below  the  level  of  the  hard  palate,  only  the  posterior 
parts  of  the  inferior  concha  are  visible  through  the  choanae,  and  the  inferior 
meatuses  of  the  nose  are  altogether  out  of  sight.  The  middle  and  superior 
meatuses  of  the  nose  and  the  middle  and  superior  conchce,  however,  can 
be  brought  into  view  and  their  condition  ascertained.  The  lateral  walls 
of  the  naso-pharynx  and  the  orifice's  of  the  auditory  tubes  can  also  be  fully 
inspected. 

Pars  Oralis. — The  oral  pharynx  lies  posterior  to  the  mouth 
and  tongue.     The  pharyngeal  part  of  the  tongue,  which  looks 


378  HEAD  AND  NECK 

more  or  less  directly  posteriorly,  forms  its  anterior  wall  in  its 
lower  part.  Above  this  is  the  isthmus  of  the  fauces,  or 
the  opening  into  the  mouth,  limited  on  either  side  by  the 
glosso-palatine  arch.  These  arches  may  be  regarded,  there- 
fore, as  the  lateral  boundary  lines  between  the  mouth  and  the 
pharynx.  On  the  lateral  wall  of  the  oral  pharynx  the  pharyngo- 
palatine  arch  forms  a  prominent  fold  which  is  gradually  lost 
as  it  is  traced  downwards.  Within  this  fold  is  the  pharyngo- 
palatine  muscle.  This  is  an  important  relation,  because  the 
posterior  palatine  arches  form  the  lateral  boundaries  of 
the  pharyngeal  isthmus,  and  by  the  contraction  of  the 
pharyngo-palatine  muscles  the  two  posterior  arches  can  be 
approximated  until  the  opening  of  the  isthmus  is  obliterated ; 
the  passage  of  food  and  fluids  from  the  oral  pharynx  into 
the  naso-pharynx  is  thus  prevented. 

The  arcus  glosso-palatinus  and  the  arcus  pharyngo-palatinus 
form,  on  each  lateral  wall  of  the  oral  pharynx,  the  anterior  and 
posterior  limits  of  a  triangular  interval  in  which  is  lodged  the 
tonsil.  The  upper  part  of  this  area,  above  the  level  of  the 
tonsil,  presents  a  small  depression  termed  the  supra-tonsillar 
fossa. 

In  the  child,  and  not  uncommonly  in  the  adult,  a  triangular 
fold  of  mucous  membrane,  the  plica  triangularis^  extends 
posteriorly  from  the  lower  part  of  the  glosso-palatine  arch 
and  the  base  of  the  tongue  across  the  surface  of  the  tonsil. 
The  upper  border  of  the  fold  may  be  free  or  it  may  become 
attached  to  a  greater  or  less  extent  to  the  surface  of  the 
tonsil. 

Pars  Laryngea. — The  laryngeal  portion  of  the  pharyngeal 
cavity  diminishes  rapidly  in  width  to  the  level  at  which  it  be- 
comes continuous  with  the  oesophagus.  In  its  anterior  wall,  from 
above  downwards,  may  be  seen:  (i)  the  epiglottis;  (2)  the 
superior  aperture  of  the  larynx  with  the  recessus  piriformis  on 
either  side ;  and  (3)  the  posterior  surfaces  of  the  arytsenoid 
and  cricoid  cartilages,  covered  with  muscles  and  mucous 
membrane. 

Aditus  Laryngis. — The  superior  aperture  of  the  larynx^ 
situated  below  the  pharyngeal  part  of  the  tongue,  is  a 
large,  obliquely  placed  opening  which  slopes  rapidly  from 
above  downwards  and  posteriorly.  It  is  somewhat  triangular 
in  outline,  and  the  basal  part  of  the  opening,  placed  above  and 
anteriorly,   is  formed  by   the   free  border   of  the  epiglottis. 


PHARYNX 


379 


Posteriorly,  the  opening  rapidly  narrows,  and  finally  ends  in 
the  interval  between  the  two  arytasnoid  cartilages.  The 
sides  of  the  aperture  are  formed  by  two  sharp  and  prominent 
folds  of  mucous  membrane,  termed  the  ary -epiglottic ^  folds, 
which  connect  the  lateral  margins  of  the  epiglottis  with  the 
arytsenoid  cartilages.  Two  small  nodules  of  cartilage,  in  the 
posterior  part  of  each  ary-epiglottic  fold,  give  rise  to  two 
rounded  eminences,  of  which  the  anterior  is  the  cimeiform 
tubercle,  and  the  posterior  the  corniculate  tubercle. 

On  either  side  of  the  lower  part  of  the  laryngeal  open- 
ing there  is  a  small  three  -  sided  or  pyramidal  depression, 
called    the   recessus  piriformis.       On    the    lateral    side    it    is 


Thyreo-hyoid  membrane 
Plica  vocalis 
Processus  vocalis 
Arytaenoid  cartilage 

Platysma 
Posterior  wall 
of  pharynx 
Retropharyn- 
geal space 

Carotid  sheath 


Sterno-hyoid 

^■^^  Thyreo-hyoid 
'^       ^  Th}-reoid  cartilage 

Omo-hyoid 

Recessus  piriformis 
Superior  thjTeoid 

Descendens 
>^  hypoglossi 
^!^^^!"-     Common  carotid 
^^/.'^^^<\V-.  Internal  jugular 


Vagus 


Scalenus  anterior 

Longus  colli 


Vertebral  artery- 


Sympathetic  trunk 


Fig.  151.— Transverse  section  through  the  Neck  at  the  level  of  upper 
part  of  the  Thyreoid  Cartilage. 

bounded  by  the  posterior  part  of  the  lamina  of  the  thyreoid 
cartilage  and  the  thyreo-hyoid  membrane ;  on  the  medial  side 
by  the  arytcenoid  cartilage  and  the  ary-epiglottic  fold  ;  whilst  its 
posterior  wall  is  formed  by  the  posterior  wall  of  the  pharynx, 
when  this  is  in  place.  The  recessus  piriformis  presents  a 
wide  entrance,  which  looks  upwards  ;  but  it  rapidly  narrows 
towards  the  bottom  (Figs.  150  and  151):  and  it  is  important  to 
the  surgeon  because  in  this  Uttle  pocket  foreign  bodies  intro- 
duced into  the  pharynx  are  liable  to  be  caught. 

Below  the  opening  of  the  larynx,  the  anterior  and  posterior 
walls  of  the  pharynx  are  always  closely  applied  to  each  other, 
except  during  the  passage  of  food. 

The  (esophageal  ope?iing  is  placed  opposite  the  lower  border 


38o  HEAD  AND  NECK 

of  the  cricoid  cartilage.  This  is  the  narrowest  part  of  the 
pharynx. 

Velum  Palatinum. — The  soft  palate  is  a  movable  curtain, 
which  projects  downwards  and  posteriorly  into  the  pharynx. 
During  deglutition  it  is  raised,  and  helps  to  shut  off  the 
nasal  part  of  the  pharynx  from  the  portion  below.  Anteriorly^ 
it  is  attached  to  the  posterior  margin  of  the  hard  palate ;  on 
each  side  it  is  connected  with  the  lateral  wall  of  the  pharynx ; 
whilst  posteriorly  it  presents  a  free  border.  From  the  centre 
of  this  free  margin  the  conical  process,  termed  the  uvula^ 
projects  ;  whilst  the  sharp  concave  part  of  the  border,  on  either 
side  of  the  uvula,  becomes  continuous  with  the  pharyngo- 
palatine  arch,  which  descends  on  the  side  wall  of  the  pharynx. 
The  upper  surface  of  the  soft  palate  is  convex  and  continuous 
with  the  floor  of  the  nasal  cavities ;  the  inferior  surface  is 
concave  and  forms  part  of  the  vaulted  roof  of  the  mouth. 
From  the  posterior  part  of  this  surface  on  each  side  a  glosso- 
palatine  arch  curves  downwards ;  and  along  its  median  plane 
may  be  seen  a  slightly  marked  median  ridge  or  raphe. 

The  soft  palate  is  composed  of  a  fold  of  mucous  membrane, 
between  the  two  layers  of  which  are  interposed  muscular, 
aponeurotic,  and  glandular  structures,  together  with  blood 
vessels  and  nerves. 

{The  two  levatores  veli  palatini. 
The  two  tensores  veli  palatini. 
The  two  glosso-palatini. 
The  two  pharyngo-palatini. 
The  musculus  uvulse. 
Palatal  aponeurosis. 
Palatal  glands. 

Ascending  palatine  from  external  maxillary. 


.        .  J  Palatine  branch  from  ascending  pharyngeal. 

'     ■       j  Twigs  from  the  descending  palatine  branch  of  the  internal 
V.      maxillary. 

(  Middle  palatine,    .         •         .\ 
^  I  Posterior  palatine,  .  .  I  from  the  spheno  -  palatine 

'       ■       \   Branches     from     pharyngeal  j  ganglion. 

i.      plexus,        .  .  .  .  j 

The  racemose  ?nucous  glands  in  the  soft  palate  form  a  very 
thick  layer,  immediately  subjacent  to  the  mucous  membrane 
which  clothes  its  inferior  surface.  Close  to  the  posterior 
border  of  the  hard  palate  the  soft  palate  contains  very  few 
muscular  fibres ;  there  it  is  composed  chiefly  of  the  two 
layers  of  mucous  membrane  enclosing  the  glands,  and  the 
palatal  aponeurosis. 


PHARYNX  381 

Dissection. — The  dissection  of  the  soft  palate  is  difficult,  and  it  is  only 
in  a  fresh  part  that  the  precise  relations  of  the  different  muscular  layers 
can  be  made  out.  Begin  by  rendering  it  tense  by  means  of  a  hook,  and 
then  remove  carefully  the  mucous  membrane  from  its  upper  and  lower 
surfaces,  and  also  from  the  glosso-  and  pharyngo-palatine  arches.  The 
latter  proceeding  will  expose  the  glosso  -  palatine  and  the  pharyngo- 
palatine  muscles  on  each  side. 

Musculus  Glosso -palatinus. — The  glosso -palatinus  is  a 
delicate  muscular  slip,  which  arises  from  the  side  of  the 
posterior  part  of  the  tongue  and  curves  upwards  and  medially 
to  reach  the  under  surface  of  the  soft  palate,  above  the 
glandular  layer.  There  its  fibres  spread  out  and  become 
continuous  with  the  corresponding  fasciculi  of  the  opposite 
side.  It  forms  the  lowest  muscular  stratum  of  the  soft 
palate. 

Musculus  Pharyngo- palatinus. — The  pharyngo- palatinus 
forms  two  muscular  strata  in  the  soft  palate  which  enclose, 
between  them,  the  musculus  uvulse  and  the  levatores  palati 
muscles.  The  upper  layer  vs,  very  weak  and  confined  to  the 
posterior  part  of  the  velum.  It  constitutes  the  most  super- 
ficial muscular  stratum  on  the  upper  aspect  of  the  soft  palate, 
and  becomes  continuous  with  the  corresponding  portion  of  the 
muscle  of  the  opposite  side.  The  deeper  layer  takes  origin 
from  the  posterior  margin  of  the  palate  bone  and  from  the 
palatal  aponeurosis,  and  some  of  its  fibres  mingle  with  those 
of  the  corresponding  muscle  of  the  opposite  side.  Lateral  to 
the  soft  palate  the  two  strata  come  together,  and  are  joined 
by  one  or  two  delicate  muscular  slips  which  spring  from  the 
lower  border  of  the  cartilage  of  the  auditory  tube.  These 
slips  are  sometimes  described  as  the  salpingo-pharyngeiis  muscle. 
The  pharyngo-palatinus,  thus  formed,  arches  downwards  and 
posteriorly  in  the  posterior  arch  of  the  fauces,  and  spreads 
out  into  a  thin  sheet  of  fibres  in  the  wall  of  the  phar}mx. 
Blending  to  some  extent  with  the  stylo-pharjmgeus,  it  is  inserted 
into  the  posterior  border  of  the  thyreoid  cartilage.  Some  of 
its  fibres,  however,  incline  posteriorly  and  are  inserted  into 
the  phar}^ngeal  aponeurosis. 

Musculus  Uvulae. — This  delicate  muscle  is  placed  on  the 
upper  aspect  of  the  soft  palate,  and,  posteriorly,  it  is  covered 
by  the  superficial  fibres  of  the  pharyngo-palatinus.  These 
must  be  removed  to  expose  it  fully.  It  consists  of  two 
minute  slips  which,  as  a  rule,  arise  from  the  posterior  nasal 
spine  of  the  hard  palate,  and  lie  one  on  either   side  of  the 


382  HEAD  AND  NECK 

median  plane.     As  they  pass  posteriorly  into  the  uvula  they 
unite  into  a  single  rounded  muscular  bundle. 

Dissection. — The  levator  palati  muscle  has  been  seen  already  on  the 
outer  aspect  of  the  pharynx  in  the  sinus  of  Morgagni.  To  display  it  from 
the  inside  it  is  necessary  to  remove  the  wall  of  the  pharynx  between  the 
auditory  tube  above  and  the  upper  border  of  the  superior  constrictor 
below,  and  then  follow  its  fibres  into  the  soft  palate.  In  a  well-injected 
subject  the  dissector  will  observe  the  ascending  palatine  artery  in  rela- 
tion to  this  muscle. 

Musculus  Levator  Veli  Palatini.  —  The  levator  palati  is  a 
rounded  fleshy  muscle  which  arises  from  the  lower  and  medial 
border  of  the  cartilage  of  the  auditory  tube,  and  from  the 
rough  surface  on  the  under  aspect  of  the  apex  of  the  petrous 
part  of  the  temporal  bone.  It  passes  downwards  and  an- 
teriorly, crosses  the  upper  border  of  the  superior  constrictor, 
pierces  the  pharyngeal  aponeurosis,  passes  below  the  orifice  of 
the  auditory  tube  and  enters  the  soft  palate.  There  its  fibres 
spread  out  below  the  uvular  muscle  and  above  the  anterior 
or  deep  portion  of  the  pharyngo-palatinus.  Anteriorly,  some 
of  the  fibres  are  inserted  into  the  palatal  aponeurosis ;  but 
more  posteriorly,  the  majority  of  the  fibres  become  continu- 
ous with  the  corresponding  fasciculi  of  the  opposite  side. 

Musculus  Tensor  Veli  Palatini. — The  origin  of  the  tensor 
veli  palatini  and  the  relations  of  its  muscular  belly  were  noted  on 
p.  293.  The  muscle  descends  from  the  base  of  the  skull  along 
the  lateral  surface  of  the  medial  pterygoid  lamina,  and  ends 
in  a  tendon  which  turns  horizontally  towards  the  median  plane, 
below  the  hamulus,  where  a  bursa  mucosa  facilitates  the  play 
of  the  tendon  on  the  bone.  In  the  soft  palate  the  tendon  ex- 
pands below  the  lower  layer  of  the  pharyngo-palatinus,  and  some 
of  its  fibres  blend  with  the  palatal  aponeurosis  whilst  others 
gain  attachment  to  the  horizontal  part  of  the  palate  bone. 

Palatal  Aponeurosis. — The  palatal  aponeurosis  extends 
posteriorly  from  the  posterior  margin  of  the  hard  palate  to 
give  strength  and  support  to  the  soft  palate.  At  first  it 
is  strongly  marked,  but  it  weakens  rapidly  as  it  passes 
posteriorly.  The  small  portion  of  the  soft  palate  which  it 
supports  contains  few  muscular  fibres,  and  remains  always 
more  or  less  horizontal  in  position.  The  much  more  extensive 
posterior  muscular  part  of  the  soft  palate  constitutes  the 
movable  sloping  portion.  The  tensor  palati  operates  upon 
the  anterior  aponeurotic  portion  of  the  soft  palate. 


PHARYNX  383 

Vessels  and  Nerves  of  the  Soft  Palate. — The  ascending 
palatine  brafich  of  the  external  maxillary  artery  is,  as  a  rule, 
the  principal  artery  of  supply  to  the  soft  palate.  It  has 
already  been  traced  on  the  wall  of  the  pharynx  (p.  299), 
where  it  lies  in  the  sinus  of  Morgagni,  in  relation  to  the 
levator  palati  muscle,  which  it  accompanies  into  the  soft  palate. 
T\\Q.  palatine  branch  of  the  ascending  pharyngeal  artery  may 
also  be  traced  into  the  soft  palate.  In  cases  where  the 
preceding  artery  is  small,  this  twig  will  be  found  enlarged 
so  as  to  take  its  place  (p.  304).  The  descefidifig  palatine 
branch  of  the  internal  maxillary  artery  also  sends  small  twigs 
to  the  soft  palate  and  tonsil. 

Two  nerves  enter  the  soft  palate  from  the  spheno-palatine  ganglion — viz. 
the  posterior  palafme  and  the  middle  palatine  nerve.  It  would  appear, 
however,  that  they  do  not  supply  the  muscles,  but  are  distributed  to  the 
mucous  membrane.  The  levator  palati,  the  musculus  uvuIk,  the  glosso- 
palatinus,  and  the  pharyngo-palatinus  are  supplied  by  twigs  from  the 
pharyngeal  branches  of  the  vagus,  which  convey  to  them  fibres  which  are 
originally  derived  from  the  cerebral  part  of  the  accessory  nerve  {v.  p.  315) 
(W.  Aldren  Turner).  The  tensor  palati  is  probably  supplied  by  the 
branch  which  it  receives  from  the  otic  ganglion,  which  conveys  to  it  fibres 
originally  derived  from  the  motor  part  of  the  trigeminal  nerve. 

TonsiUae  Palatinae. — The  palatine  tonsils  are  two  prominent 
masses  of  lymphoid  tissue,  placed  one  on  each  lateral  wall 
of  the  pharynx,  in  the  triangular  interval  between  the  two 
palatine  arches  and  immediately  above  the  pharyngeal  part 
of  the  tongue.  The  pharyngeal  or  internal  surface  of  the 
tonsil  is  covered  with  mucous  membrane  and  presents  a 
number  of  orifices  which  lead  into  crypts  or  recesses  in  its 
substance.  The  deep  or  external  surface  is  embedded  in  the 
pharyngeal  wall  and  is  supported  by  the  superior  constrictor 
muscle  of  the  pharynx  (see  p.  298).  It  is  covered  by  a  layer 
of  fibrous  tissue  which  forms  an  incomplete  capsule  for  the 
organ.  It  is  important  to  note  that  between  the  tonsil  and 
the  superior  constrictor  there  is  some  lax  connective  tissue,  so 
that  the  organ  can  be  pulled  forwards  by  the  volsellum  with- 
out dragging  the  wall  of  the  pharynx  with  it. 

The  tonsils  have  a  rich  blood-supply.  They  derive  arterial 
twigs  from  the  tonsillar  and  ascending  palatine  branches  of 
the  external  maxillary,  the  descending  palatine  branch  of  the 
internal  maxillary,  the  ascending  pharyngeal,  and  the  dorsalis 
linguae. 

Tuba    Auditiva    (O.T.    Eustachian    Tube). — This    is    the 


384  HEAD  AND  NECK 

canal  which  conveys  air  from  the  pharynx  to  the  tympanic 
cavity.  It  is  divided  into  two  portions,  according  to  the  parts 
which  enter  into  the  construction  of  its  wall.  Thus,  in  the 
lateral  part  of  its  course,  as  it  nears  the  tympanic  cavity,  its 
wall  is  bony,  and  it  runs  in  the  interval  between  the  tympanic 
and  petrous  portions  of  the  temporal  bone.  The  medial  part 
consists  mainly  of  cartilage.  It  is  placed  on  the  base  of  the 
skull,  and  is  lodged  in  the  gutter  or  groove  between  the 
petrous  part  of  the  temporal  bone  and  the  great  wing  of  the 
sphenoid.  This  is  the  subdivision  of  the  tube  which  comes 
under  the  notice  of  the  dissector  at  the  present  stage,  and 
he  should  first  note  its  direction  and  then  study  its  relations 
and  the  construction  of  its  wall. 

The  direction  of  the  canal  can  be  readily  ascertained  by 
passing  a  probe  into  it  through  its  pharyngeal  orifice.  It  runs 
postero-laterally  with  a  slight  inclination  upwards  and  passes 
first  above  and  then  to  the  lateral  side  of  the  levator  palati, 
and  along  the  medial  side  of  the  upper  part  of  the  tensor  palati. 
It  lies,  therefore,  in  a  considerable  part  of  its  extent  between 
the  two  muscles. 

Before  removing  the  mucous  membrane  from  the 
pharyngeal  part  of  the  tube  the  dissector  should  note  that  at 
the  lower  margin  of  the  orifice  there  is  a  prominent  rounded 
eminence,  the  levator  cushion^  due  to  the  subjacent  levator  veli 
palatini.  The  removal  of  the  mucous  membrane  will  reveal  the 
fact  that  the  wall  of  the  tube  is  formed,  in  great  part,  by  a 
triangular  plate  of  cartilage,  which  is  folded  upon  itself  so 
as  to  protect  the  tube  on  its  upper  and  medial  aspects.  The 
cartilage  is  deficient  below  and  laterally,  its  place  being 
taken  by  dense  fibrous  tissue,  which  connects  the  margins 
of  the  cartilage  and  completes  the  wall  of  the  canal.  The 
projecting  free  base  of  the  cartilage  gives  rise  to  the  torus 
tubarius  already  examined  on  the  lateral  wall  of  the  naso- 
pharynx (p.  376).  A  muscular  slip,  which  descends  from  the 
lateral  margin  of  the  cartilage,  in  relation  to  the  outer  un- 
protected side  of  the  tube,  has  been  termed  the  dilatator  tubce 
(Rudinger).  It  joins  the  tensor  palati.  The  interior  of  the 
tube  is  lined  with  mucous  membrane  continuous  with  that 
of  the  pharynx  and  the  tympanic  cavity  ;  and  its  calibre  varies 
considerably  in  different  parts  of  its  course.  It  is  narrowest 
at  a  point  termed  the  isthmus^  situated  at  the  junction  of 
the  osseous  and  cartilaginous  parts.     As  the  tube  is  traced 


CAROTID  CANAL  385 

thence  to  the  pharynx  it  gradually  increases  in  calibre,  and  it 
attains  its  greatest  width  at  its  opening  into  the  naso-pharynx. 


CAROTID  CANAL. 

The  carotid  canal,  which  traverses  the  interior  of  the 
petrous  part  of  the  temporal  bone,  contains  the  internal 
carotid  artery,  the  internal  carotid  continuation  of  the  cervical 
sympathetic  and  a  plexus  of  veins. 

Dissection.— T\vQ  carotid  canal  may  be  opened  up  by  removing  its 
inferior  wall  with  the  bone  forceps.  In  doing  this,  it  is  not  necessary  to 
interfere  with  the  auditory  tube,  which  lies  in  close  proximity.  The  dis- 
section must  be  made  on  one  side  only. 

Arteria  Carotis  Interna. — The  internal  carotid  artery  in 
this  part  of  its  course  is  about  three-quarters  of  an  inch  long. 
At  first  it  ascends  vertically ;  then,  bending  suddenly,  it  runs 
horizontally  antero-medially.  It  emerges  from  the  canal  at 
the  apex  of  the  petrous  bone  and  enters  the  foramen  lacerum, 
where  it  turns  upwards,  pierces  the  external  layer  of  the  dura 
mater,  and  enters  the  middle  fossa  of  the  skull.  From  this 
point  onwards  the  internal  carotid  artery  has  been  examined 
already  (p.  331).  Whilst  within  the  carotid  canal  it  lies 
below  and  anterior  to  the  cochlea  and  the  tympanic  cavity. 
The  great  superficial  petrosal  nerve  and  the  semilunar 
ganglion  are  placed  above  it,  but  are  separated  from  it  by  a 
thin  plate  of  bone,  which  is,  however,  sometimes  absent. 

Nervus  Caroticus  Internus. — The  dissector  has  already 
noted  this  large  branch  proceeding  from  the  upper  end  of 
the  superior  cervical  ganglion  and  entering  the  carotid  canal 
with  the  internal  carotid  artery.  It  divides  ^  almost  im- 
mediately into  two  parts,  which  are  placed  on  either  side  of 
the  artery.  Each  of  these  soon  divides  into  a  number  of 
branches  which  communicate  together  around  the  internal 
carotid  artery  forming  the  interfial  carotid  plexus.  The 
further  dissection  of  these  branches  is  a  matter  of  some 
difficulty,  and  can  be  satisfactorily  effected  only  under 
specially  favourable  circumstances. 

At  the  posterior  end  of  the  cavernous  sinus  a  ganglion  is  sometmies 
found  in  the  plexus,  and  where  the  sixth  nei-ve  crosses  the  internal  carotid 
artery  the  plexus  is  very  dense.  This  part  is  known  as  the  cavernous 
plexus.       At  the  anterior  end  of  the  cavernous   sinus  the  carotid  plexus 

VOL.  II — 25 


386  HEAD  AND  NECK 

breaks  up  into  branches  which  accompany  the  anterior  and  middle  cerebral 
arteries. 

The  internal  carotid  plexus  communicates  with  the  tympanic  plexus  by 
means  of  superior  and  inferior  carotico-tympanic  branches  given  off  in  the 
carotid  canal,  and  with  the  spheno-palatine  ganglion  by  the  great  deep 
petrosal  branch,  which  unites  with  the  great  superficial  petrosal  of  the  facial 
nerve  to  form  the  nerve  of  the  pterygoid  canal  (O.T.  Vidian).  It  gives 
branches  also  to  the  semilunar  ganglion,  the  third,  fourth,  sixth  and  the 
ophthalmic  branch  of  the  fifth  nerve,  and  a  branch  which  accompanies  the 
naso-ciliary  nerve  into  the  orbit  and  joins  the  ciliary  ganglion. 


NERVUS  MAXILLARIS. 

As  the  maxillary  nerve  passes  anteriorly,  from  the  semilunar 
ganglion  to  the  face,  it  traverses  the  foramen  rotundum,  the 
upper  part  of  the  pterygo-palatine  fossa,  the  pterygo-maxillary 
fissure,  the  inferior  orbital  fissure  and  the  infra-orbital  canal. 
The  dissector  should  therefore  proceed  to  expose  the  nerve 
in  these  localities. 

Dissection. — Remove  the  temporal  muscle  and  the  upper  head  of  the 
external  pterygoid  muscle,  and,  placing  the  saw  upon  the  cut  margin  of  the 
skull  at  a  point  immediately  above  the  external  meatus,  carry  it  obliquely 
downwards  and  anteriorly  through  the  squamous  part  of  the  temporal 
bone  and  the  great  wing  of  the  sphenoid,  towards  the  medial  end  of  the 
superior  orbital  fissure.  This  saw-cut  should  enter  the  superior  orbital 
fissure  immediately  to  the  lateral  side  of  the  foramen  rotundum.  A 
second  saw-cut  should  then  be  made  from  the  cut  margin  of  the  cranial 
wall,  immediately  above  the  anterior  margin  of  the  great  wing  of  the 
sphenoid  bone,  downwards  into  the  superior  orbital  fissure  to  meet  the  first 
saw-cut.  The  wedge-shaped  piece  of  bone  included  between  these  cuts 
can  now  be  removed.  Additional  space  may  be  obtained,  and  the  pterygo- 
palatine fossa  may  be  more  fully  opened  up,  by  removing  what  remains  of 
the  great  wing  of  the  sphenoid  upon  the  lateral  side  of  the  foramen  rotundum, 
but  the  circumference  of  this  aperture  must  be  carefully  preserved.  Proceed, 
in  the  next  place,  to  open  up  the  infra-orbital  canal.  In  its  posterior  part 
its  upper  wall  is  usually  so  thin  that  it  can  easily  be  removed  by  a  pair 
of  dissecting  forceps,  but  anteriorly  it  sinks  deeply  under  the  lower  part  of 
the  rim  of  the  orbital  opening,  and  here  the  chisel  must  be  employed. 
The  maxillary  nerve  can  now  be  defined  and  its  branches  displayed. 
The  infra  -  orbital  artery  and  vein,  which  accompany  the  nerve  in  the 
infra-orbital  canal,  will  be  exposed  at  the  same  time. 

Nervus  Maxillaris. — The  maxillary  nerve  springs  from  the 
semilunar  ganglion  within  the  cranial  cavity  (p.  330).  It  is 
composed  entirely  of  sensory  fibres,  and  passes  anteriorly, 
outside  the  dura  mater  and  in  relation  to  the  lower  part  of  the 
cavernous  sinus,  to  the  foramen  rotundum  through  which  it 
enters  the  pterygo-palatine  fossa.  It  crosses  the  upper  part 
of  this  fossa,   curves   laterally  through  the  pterygo-maxillary 


NERVUS  MAXILLARIS 


387 


fissure  into  the  infra-temporal  fossa,  and,  near  the  middle 
of  the  inferior  orbital  fissure,  enters  the  infra-orbital  canal, 
where  it  receives  the  name  of  iiifra-orbital.  The  infra- 
orbital canal  traverses  the  floor  of  the  orbit,  which,  it  should 
be  remembered,  forms  the  roof  of  the  maxillary  sinus 
also.  Finally,  the  nerve  emerges  upon  the  face  through 
the  infra-orbital  foramen,  and  breaks  up,  under  cover  of  the 
quadratus  labii  superioris,  into  numerous  branches  which 
form  a  dense   plexus  with  twigs  from  the  facial  nerve.     Its 


Zj-gomatic  nerve 

Maxillary  nerve       > 
Ophthalmic  nerve      ]  \ 

Meningeal  branch  of  maxillary  nerve 
Sensory  root  [ 

Motor  root  of  ^ 
trigeminal 


Semilunar  ganglion  -' 
INIandibular  nerve 


Posterior  superior  alveolar 
Infra-orbita 

Zygomatico-temporal 
1       Zygomatico-facial 
1       \         Middle  superior  alveolar 
Anterior  superior 
alveolar 


Spheno-palatine  ganglion ' 

Post,  palatine 

Middle  palatine 

Ant.  palatine 


Palpebral 
branches 

Nasal 
-'  branches 
Labial 
'^M^ branches 


Fig.  152. — Diagram  of  the  Maxillary  Nerve, 


terminal  filaments  are  distributed  to  the  lower  eyefid,  the 
nose,  and  the  upper  lip.  The  course  of  the  maxillary  nerve 
may  be  separated  into  five  stages,  in  each  of  which  branches 
are  given  off.     These  are  : — 

1.  Within  the  cranium,    {Meningeal  (p.  330). 

2.  In  the  ptervTO-pala-    To  1  1  4.- 

tine  fossa;     .         .    \  Spheno-palatme. 

3.  In  the  infra-temporal  /Zygomatic  (already  described). 

fossa,  .       ^.         .    \  Posterior  superior  alveolar. 

4.  In  the  infra-orbital      (Middle  superior  alveolar. 

canal,  .         .  .    (Anterior  superior  alveolar. 

i  Palpebral, 

5.  In  the  face,     .         .    4  Nasal,         \  already  described. 

(^  Labial, 


388  HEAD  AND  NECK 

The  zygomatic  nerve,  which  has  already  been  dissected 
in  the  orbit,  can  now  be  traced  to  its  origin  from  the 
maxillary  nerve  in  the  infra-temporal  fossa.  The  spheno- 
palatine branches  are  two  stout  twigs  which  arise  from  the 
under  aspect  of  the  maxillary  nerve,  and  proceed  vertically 
downwards,  in  the  pterygo-palatine  fossa,  to  the  spheno-palatine 
ganglion,  of  which  they  constitute  the  sensory  roots. 

Nervi  Alveolares  Superiores. — These  are  usually  three  in 
number,  and  are  distinguished  as  posterior,  middle,  and 
anterior.  The  middle  superior  alveolar  nerve  is  sometimes 
absent  as  a  separate  trunk,  in  which  case  it  arises  in  common 
with  the  anterior  superior  alveolar  branch. 

The  posterior  superior  alveolar  nerve  takes  origin  in  the 
infra-temporal  fossa,  and  almost  immediately  divides  into 
two  branches,  which  proceed  downwards  upon  the  posterior 
aspect  of  the  body  of  the  maxilla.  They  contribute  a  few 
fine  filaments  to  the  mucous  membrane  of  the  cheek  and 
to  the  gum,  and  then  disappear  into  the  minute  posterior 
dental  foramina  to  supply  the  three  molar  teeth  and  the  lining 
membrane  of  the  maxillary  sinus. 

The  middle  superior  alveolar  nerve  supplies  the  two 
premolar  teeth.  It  arises  from  the  infra-orbital  nerve,  and 
can  be  easily  detected  (when  present)  by  gently  raising  the 
parent  trunk  from  the  floor  of  the  infra-orbital  canal.  It 
descends  in  a  minute  canal  which  traverses  the  lateral  wall 
of  the  maxillary  sinus. 

The  anterior  superior  alveolar  nerve,  much  the  largest  of 
the  three  alveolar  branches,  springs  from  the  infra-orbital  as  it 
approaches  the  anterior  part  of  the  canal.  It  can  be  brought 
into  view  by  raising  the  parent  trunk  from  the  floor  of  the 
canal,  and  it  will  then  be  seen  to  enter  a  special  bony  tunnel 
which  traverses  the  maxilla  in  the  anterior  wall  of  the 
maxillary  sinus.  The  dissector  should  endeavour  to  open 
up  this  canal  with  the  chisel.  After  supplying  a  branch  to 
the  mucous  membrane  of  the  lower  and  anterior  part  of 
the  nasal  cavity,  the  anterior  superior  alveolar  nerve  divides 
into  branches  for  the  incisor  and  the  canine  teeth. 

While  traversing  the  maxilla,  the  three  superior  alveolar  branches 
communicate  with  each  other,  and  form  two  nerve-loops  (Fig.  152). 
Numerous  twigs  proceed  from  these,  and  join  in  a  fine  plexus.  It  is  from 
this  plexus  that  the  terminal  filaments  to  the  teeth  and  gum  take  origin. 

Arteria    Infra -orbitalis. — The    infra- orbital    artery    is    a 


NASAL  CAVITIES  389 

branch  of  the  internal  maxillary.  It  arises  in  the  pterygo- 
palatine fossa  and  accompanies  the  infra-orbital  nerve.  In 
the  face  its  terminal  twigs  anastomose  with  branches  of  the 
external  maxillary,  transverse  facial,  and  buccinator  arteries  ; 
in  the  infra-orbital  canal  it  gives  some  fine  branches  to  the 
contents  of  the  orbital  cavity,  and  also  the  anterior  superior 
alveolar  artery  which  accompanies  the  nerve  of  that  name, 
and  supplies  the  incisor  and  canine  teeth,  and  the  lining 
membrane  of  the  maxillary  sinus. 

The  infra-orbital  vein  joins  the  pterygoid  plexus. 


NASAL  CAVITIES. 

Dissection. — The  portion  of  the  mandible  which  still  remains,  together 
with  the  tongue  and  larynx,  must  now  be  removed  from  the  upper  part  of 
the  skull.  From  the  angle  of  the  mouth  on  each  side  carry  the  knife 
posteriorly,  through  the  buccinator  and  the  mucous  membrane  of  the  cheek, 
the  pterygo-mandibular  raphe,  and  the  lateral  wall  of  the  pharynx.  The 
internal  pterygoid  muscle  has  been  divided  already,  but  it  will  be  necessary 
to  cut  the  internal  carotid  artery,  the  smaller  vessels  which  are  still  un- 
divided and  the  nerves  which  still  connect  the  pharynx  with  the  skull.  The 
larynx  and  tongue  must  be  laid  aside  for  future  dissection. 

The  anterior  part  of  the  skull  should  next  be  divided  into  two  lateral  parts 
by  sawing  through  it  in  the  sagittal  direction  close  to  one  side  of  the  nasal 
septum.  As  a  general  rule  the  nasal  septum  is  not  vertical,  but  deviates 
more  or  less  to  one  or  other  side  of  the  median  plane.  This  deviation  is 
more  frequently  directed  to  the  right  than  to  the  left  side.  Endeavour  to 
determine  the  direction  which  it  takes  in  the  skull  under  observation, 
by  passing  a  probe  into  the  nasal  cavity  through  the  choanal.  The 
section  through  the  skull  should  be  made  close  to  the  concave  side  of  the 
septum.  Begin  anteriorly  by  introducing  a  knife  into  the  nostril  of  that  side, 
and  carry  it  upwards  through  the  cartilaginous  part  of  the  nose  to  the  nasal 
bone.  Then  place  the  specimen  so  that  the  face  rests  upon  the  table,  and 
divide  the  soft  palate  in  the  median  plane.  The  section  may  now  be 
completed  by  sawing  through  the  hard  palate  and  bony  roof  of  the  nasal 
cavity  to  the  side  of  the  median  plane.  The  dissector  should  make  every 
effort  to  preserve  the  septum  of  the  nose  intact.  As  a  general  rule  the 
upper  concha  is  partially  injured.  This  is  not  a  very  serious  matter,  as 
the  lateral  aspect  of  the  nasal  cavity  can  be  studied  upon  the  opposite  side 
when  the  septum  of  the  nose  has  been  removed. 

Septum  Nasi. — The  nasal  septum  divides  the  cavity  of 
the  nose  into  two  narrow  chambers — the  right  and  left  nasal 
cavities.  It  is  not  placed  accurately  in  the  median  plane, 
but  almost  invariably  shows  a  bulging  or  deviation  to  one 
or  other  side  (inore  frequently  to  the  right  side).  Im- 
mediately above  the  orifice  of  the  nostril  or  anterior  aperture 
of   the  nasal    cavity,  the  septum  shows   a  slight   depression, 


39° 


HEAD  AND  NECK 


which  corresponds  to  the  vestibule  of  the  nose,  and  forms 
the  medial  wall  of  this  subdivision  of  the  nasal  cavity. 
The  vestibular  part  of  the  partition  is  clothed  with  skin, 
continuous  with  the  external  integument ;  from  this  a 
number  of  stiff  hairs,  termed  vibrisscB,  project.  Over  the 
rest  of  its  extent  the  septum  nasi  is  covered  with  mucous 
membrane,  which  is  closely  adherent  to  the  subjacent  peri- 
osteum   forming    with    it    a     muco  -  periosteum ;    and    it    is 


Frontal  sinus 


Nasal  bone 


Sublingual  gland 


Mandible 


Vestibule  of^L^^^ '^ 

nasal  cavity    ^^^/T/r 

Opening  of  /|l^l)) 
vomero-nasal  organ 


Septal  cartilage 

Perpendicular  lamina  of  ethmoid 
Vomer 

Sphenoidal  air  sinus 


\iW*Wi^  Levator  cushion 

<^'m  i    Opening  of  auditory 
-  *'-  •  *^^tube 

Lateral  pharyngeal 
recess 
Pharyngeal  tonsil 

f^-O^-^^TT'  Atlas 

^'^hJ   Soft  palate 

Transverse  ligament 

p  I  j      Epistropheus 
"v;  11 Epiglottis 

Hyoid  bone 


Fig.  153. — Antero-posterior  section  through  the  Nose,  Mouth,  and 
Pharynx,  a  little  to  the  left  of  the  median  plane. 

separable  into  two  districts,  viz.,  a  lower  or  respiratory 
area,  and  a  much  smaller  upper  or  olfactory  area,  comprising 
not  more  than  the  upper  third  of  the  septum,  in  which 
branches  of  the  olfactory  nerve  spread  out.  The  respiratory 
mucous  membrane  is  very  thick  and  spongy.  It  is  highly 
vascular  and  contains  numerous  mucous  glands.  The  minute 
orifices  of  the  gland  ducts  can  be  detected  by  the  naked 
eye.  Over  the  olfactory  district  of  the  septum  the  mucous 
membrane  is  softer  and  more  delicate,  and  not  so  thick.  In 
the  fresh  state  it  presents  a  yellowish  colour,  and  the  glands 
are  smaller. 


NASAL  CAVITIES  391 

In  favourable  cases  a  minute  orifice  may  be  detected  in  the  mucous 
membrane,  on  the  lower  and  anterior  part  of  the  nasal  septum,  immediately- 
posterior  to  the  vestibular  area.  It  is  placed  above  the  anterior  end  of  a 
well-marked  elongated  projection  which  passes  obliquely  posteriorly  and 
upwards,  and  corresponds  to  the  thickened  lower  margin  of  the  septal 
cartilage.  This  aperture  varies  in  diameter  from  ^  mm.  to  i^  mm. 
(Schwalbe).  It  leads  into  a  narrow  canal,  which  passes  posteriorly  for 
a  short  distance,  and  then  ends  blindly.  It  is  of  interest  because  it 
represents  in  the  human  subject  the  rudiment  of  the  vonuro-iiasal  organ 
(O.T.  organ  of  Jacobson),  a  tubular  structure  which  is  highly  developed  in 
some  of  the  lower  animals. 

Construction  of  tlie  Nasal  Septum. — Strip  the  muco- 
periosteum  from  the  exposed  surface  of  the  septum  nasi  and 
the  parts  forming  the  septum  will  be  rendered  visible.  The 
bulk  of  the  partition  is  composed  of  the  perpendicular  lamina 
of  the  ethmoid  and  the  vomer  posteriorly,  and  of  the  septal 
cartilage  anteriorly.  Small  portions  of  other  bones  take  a 
minor  part  in  its  construction.  Thus,  above  and  posteriorly 
there  are  the  crest  and  rostrum  of  the  sphenoid;  above  and 
anteriorly  is  the  nasal  spine  of  the  frontal  bone ;  whilst  below 
there  is  the  crest  of  bone  formed  by  the  apposition  of  the 
palatal  processes  of  the  palate  and  maxillary  bones  of  opposite 
sides. 

Cartilago  Septi  Nasi. — The  septal  cartilage  fills  up  the 
wide  angular  gap  which  intervenes  between  the  perpendicular 
lamina  of  the  ethmoid  and  the  vomer,  and  it  projects  anteriorly 
towards  the  point  of  the  nose.  It  is  a  broad  irregularly 
quadrilateral  plate.  Its  upper  and  posterior  border  is  in  ap- 
position with  the  anterior  border  of  the  perpendicular  lamina 
of  the  ethmoid  ;  its  lower  and  posterior  border,  much  thickened, 
is  received  into  the  groove  in  the  anterior  border  of  the  vomer 
and  the  nasal  crest  of  the  maxillae.  The  angle  between  these 
two  borders  is  prolonged  posteriorly,  for  a  varying  distance, 
in  the  form  of  a  tongue-shaped  cartilaginous  process,  which 
occupies  the  interval  between  the  two  plates  of  the  vomer. 
The  upper  ajid  anterior  border  of  the  septal  cartilage  is  in 
contact  above  with  the  suture  between  the  two  nasal  bones ; 
below  this  it  is  related  to  the  two  lateral  cartilages  of  the 
nose,  whilst  still  lower  down  it  is  seen  in  the  interval  between 
the  two  larger  alar  cartilages. 

Its  connection  with  the  lateral  cartilage  on  each  side  is  a  very  intimate 
one  ;  indeed,  below  the  nasal  bones,  the  three  cartilages  are  directly 
continuous,  but  lower  down  they  are  separated  by  a  fissure  which  runs 
upwards  for  some  distance  on  each  side.  The  lozver  and  anterior  border  is 
very  short ;  it  is  free,  and  extends  posteriorly  to  the  anterior  nasal  spine. 


392  HEAD  AND  NECK 

The  anterior  angle  of  the  septal  cartilage  is  blunt  and  rounded,  and  does  not 
reach  to  the  point  of  the  nose,  which  is  formed  by  the  alar  cartilages. 

The  deviation  of  the  septum  nasi  from  the  median  plane  will  now  (in  all 
probability)  be  seen  to  be  due  to  a  bulging  to  one  side  of  the  vomer  and 
perpendicular  lamina  of  the  ethmoid  along  their  line  of  union.  It  is  not 
developed  until  after  the  seventh  year. 

Dissection. — The  septal  cartilage  and  thin  bony  part  of  the  septum 
must  now  be  removed  piecemeal.  This  must  be  done  very  carefully,  as 
it  is  necessary  to  preserve  intact  the  muco-periosteum  which  clothes  the 
opposite  side  of  the  septum.  It  is  in  this  muco-periosteum  that  the  nerves 
and  blood  vessels  must  be  examined. 

Vessels  and  Nerves  of  the  Septum  Nasi. — The  following 
is  a  list  of  the  nerves  : — 

Nerves  of  Smell,      .  Olfactory. 

II.   Naso-palatine. 
2,   Medial  nasal  branch  of  the  anterior  eth- 
moidal nerve. 
3.   Nasal     branches     from     spheno- palatine 
ganglion    and    from    the   nerve    of    the 
pterygoid  canal  (O.T.  Vidian). 

The  Medial  Group  of  Olfactory  Nerves. — These  nerves  are 
distributed  in  the  muco-periosteum  of  the  upper  part  of  the  nasal 
septum  and  are  barely  distinguishable,  except  in  a  fresh  part ; 
further,  they  are  so  soft  that  it  is  hardly  possible  to  isolate 
them.  They  enter  the  nasal  cavity  through  the  medial  series 
of  apertures  in  the  cribriform  plate  of  the  ethmoid,  and  pro- 
ceed downwards  in  grooves  on  the  surface  of  the  perpen- 
dicular lamina  of  the  same  bone. 

Nervus  Naso-palatinus. — The  naso-palatine  nerve  is  a 
long  slender  twig  which  can  easily  be  detected  upon  the  deep 
surface  of  the  muco-periosteum  of  the  septum.  It  springs  from 
spheno-palatine  ganglion,  and  enters  the  nasal  cavity  through 
the  spheno-palatine  foramen.  In  the  first  part  of  its  course 
it  runs  medially  upon  the  inferior  surface  of  the  body  of  the 
sphenoid.  Having  gained  the  nasal  septum,  it  changes  its 
direction  and  passes  downwards  and  anteriorly,  in  a  shallow 
groove  on  the  surface  of  the  vomer  under  cover  of  the  muco- 
periosteum.  Finally  it  enters  the  foramen  of  Scarpa,  and, 
where  the  two  foramina  of  Scarpa  open  into  the  common 
incisive  foramen,  the  nerves  of  opposite  sides  unite  in  a  plexus 
from  which  branches  are  given  to  the  mucous  membrane 
covering  the  anterior  part  of  the  hard  palate.  The  naso- 
palatine nerve  is  accompanied  by  the  posterior  nasal  septal 
artery ;  and,  as  it  lies  on  the  surface  of  the  vomer,  it  supplies 
some  small  twigs  to  the  muco-periosteum  of  the  septum  nasi. 


NASAL  CAVITIES  393 

A  few  nasal  branches  from  the  spheno-palatine  ganglmi^  and 
also  from  the  nerve  of  the  pterygoid  canal,  reach  the  muco- 
periosteum  over  the  superior  and  posterior  part  of  the  septum. 
They  are  very  minute,  and  it  is  questionable  if  the  dissector 
will  be  able  to  discover  any  trace  of  them  in  an  ordinary  part. 

The  medial  nasal  branches  of  the  anterior  ethmoidal  nerve 
will  be  found  descending  over  the  anterior  part  of  the  nasal 
septum.     They  may  be  traced  as  far  as  the  vestibule. 

The  arteries  which  convey  blood  to  the  septum  nasi  are  : 
(i)  the  posterior  nasal  septal,  which  accompanies  the  naso- 
palatine nerve  ;  (2)  a  branch  of  the  anterior  ethmoidal  accom- 
panying the  medial  branches  of  the  anterior  ethmoidal  nerve  ; 
(3)  some  minute  twigs  to  the  upper  part  of  the  septum  from 
the  posterior  ethmoidal  artery ;  (4)  the  septal  branch  of  the 
superior  labial  artery,  which  is  distributed  upon  the  columna 
nasi. 

Dissection. — The  muco-periosteum  of  the  septum  may  now  be  divided, 
by  the  scissors,  along  the  roof  of  the  nasal  cavity.  Before  doing  this, 
disengage  from  its  surface  the  naso-palatine  nerve  and  the  medial  branches 
of  the  anterior  ethmoidal  nerve,  in  order  that  they  may  be  afterwards  traced 
to  their  origins.  When  the  layer  of  muco-periosteum,  thus  detached  from 
the  roof  of  the  nose,  is  thrown  down  the  nasal  cavity  is  exposed. 

Cava  Nasi. — The  nasal  cavities  are  two  chambers  placed 
one  on  each  side  of  the  septum  nasi.  They  are  narrow,  but 
the  vertical  depth  and  antero-posterior  length  of  each  cavity 
is  very  considerable.  The  width  increases  somewhat  from 
above  downwards;  thus,  in  the  upper  part,  the  superior 
concha  is  separated  from  the  septum  by  an  interval  of  only 
2  mm.,  whilst  lower  down  a  space  of  4  or  5  mm.  intervenes 
between  the  inferior  concha  and  the  septum.  Each  nasal 
cavity  presents  a  medial  wall  formed  by  the  septum,  a  lateral 
wall,  a  roof,  a  floor,  and  an  anterior  and  a  posterior  aperture. 

The  anterior  apertures  of  the  nasal  cavities,  or  nostrils,  are 
two  oval  orifices  which  open  upon  the  face  and  look  down- 
wards. The  posterior  apertures,  or  choance,  open  into  the  naso- 
pharynx and  look  posteriorly  and  downwards. 

The  narrow  roof  of  the  nasal  cavity  consists  of  an  inter- 
7nediate  horizontal  portion  formed  by  the  cribriform  plate  of 
the  ethmoid  bone,  and  of  an  anterior  and  a  posterior  sloping 
part.  The  anterior  part  is  formed  by  the  narrow  grooved 
nasal  surface  of  the  frontal  spine  of  the  frontal  bone,  the 
nasal  bone,  and  the  angle  between  the  lateral  cartilage  and 


394 


HEAD  AND  NECK 


the  septal  cartilage.  The  posterior  part  of  the  roof  is  com- 
posed of  the  anterior  and  under  surfaces  of  the  body  of  the 
sphenoid,  and  also  of  the  ala  of  the  vomer,  the  sphenoidal 
process  of  the  palate  bone,  and  the  vaginal  process  of  the 
medial  pterygoid  lamina,  all  of  which  are  applied  to  the  under 
surface  of  the  sphenoidal  body. 


Anterior 
ethmoidal  cell^^—^ 


Infundibulum 


Posterior  angle  of 

septal  cartilage 

between  vomer. 

and  perpendicular 

lamina  of  ethmoid 


Orbital  cavity 


Middle  meatus 
Middle  concha 


[axillary 


Inferior  meatus 

Inferior  concha 

Fig.  154. — Posterior  aspect  of  Frontal  section  through  the  Nasal 
Cavities  opposite  the  Crista  Galli  of  the  Ethmoid  Bone. 

The  lipper  arrow  shows  the  opening  of  an  anterior  ethmoidal  cell  into  the  hiatus 
semilunaris.  The  lotver  arrow  passes  from  the  maxillary  sinus  into  the  hiatus 
semilunaris. 

The  floor  of  the  nasal  cavity  is  of  considerable  width.  It  is 
formed  by  the  palatal  processes  of  the  maxilla  and  the  palate 
bones,  and  is  concave  from  side  to  side.  Further,  it  presents 
a  gentle  antero-posterior  slope,  being  slightly  higher  anteriorly 
than  posteriorly.  On  the  anterior  part  of  the  floor,  and  close 
to  the  septum  nasi,  the  dissector  may  see  a  minute  funnel- 
shaped  depression  of  the  muco-periosteum  into  the  incisive 
foramen.  This  is  of  interest  from  a  developmental  point  of 
view ;  for  it  is  a  vestige  of  the  extensive  communication  which 


NASAL  CAVITIES  395 

existed  in  the  embryo  between  the  cavities  of  the  nose  and  the 
mouth. 

Lateral  Wall  of  the  Nasal  Cavity. — The  lateral  wall  of 
the  nasal  cavity  is  rendered  uneven  and  complicated  by  the 
projection  of  the  three  conchae  (O.T.  turbinal  bones). 

The  part  which  the  different  bones  take  in  the  formation  of  the  lateral 
wall  of  the  cavity  of  the  nose  must  in  the  first  place  be  studied  in  a 
sagittal  section  through  the  macerated  skull,  and  the  dissector  should 
constantly  refer  to  such  a  preparation  during  the  dissection.  Anteriorly,  it 
is  formed  by  the  lateral  cartilage,  the  alar  cartilage,  the  nasal  bone,  and  the 
frontal  process  of  the  maxilla.  More  posteriorly  the  lacrimal,  the  ethmpid, 
and  the  inferior  concha,  with  a  small  portion  of  the  body  of  the  maxilla, 
enter  into  its  construction  ;  whilst  still  more  posteriorly  are  the  perpen- 
dicular part  of  the  palate  bone  and  the  medial  pterygoid  lamina  of  the 
sphenoid.  Placed  in  relation  to  the  lateral  aspect  of  this  wall  are  the 
ethmoidal  air-cells,  which  intervene  between  the  upper  part  of  the  nasal 
cavity  and  the  orbit,  whilst,  at  a  lower  level,  the  great  air  sinus  of  the 
maxilla,  the  maxillary  sinus,  is  situated  immediately  to  the  lateral  side  of 
the  nasal  cavity  (Fig.  154). 

Turning  now  to  the  dissection,  the  dissector  will  see  that 
the  lateral  wall  is  separable  into  three  areas  or  districts. 
These  are — (i)  the  vestibule;  (2)  the  atrium  meatus  medii ; 
(3)  the  region  of  the  conchae  and  the  intervening  meatuses. 

Vestibulum  Nasi. — The  vestibular  part  (Fig.  155,  6,  e') 
of  the  lateral  wall  is  a  depression  of  a  somewhat  oval  form 
placed  immediately  above  the  aperture  of  the  nostril.  It  is 
partially  divided  into  an  upper  and  lower  portion  by  a  short 
ridge,  which  projects  anteriorly  from  its  posterior  boundary ; 
and  it  is  clothed  throughout  with  integument  continuous  with 
the  skin.  From  this  a  number  of  stout,  stiff  hairs,  termed 
vibrissce,  project  (Fig.  155,  5).  The  vibrissae  which  spring 
from  the  anterior  part  of  the  region  incline  posteriorly,  whilst 
those  which  are  implanted  into  the  posterior  part  are  directed 
anteriorly  ;  in  this  manner  a  sieve-like  arrangement  is  provided 
at  the  anterior  aperture  of  the  nose.  The  vestibular  part  of 
the  lateral  wall  is  placed  opposite  the  corresponding  area  on 
the  septum  nasi,  and  the  two  together  constitute  an  ampuUated 
entrance  to  the  nasal  cavity.  The  capacity  and  shape  of  this 
section  of  the  cavity  is  influenced  to  a  certain  extent  by  the 
contraction  of  the  nasal  muscles. 

Atrium  Meatus  Medii. — This  part  of  the  lateral  wall  of  the 
nasal  cavity  (Fig.  155,  s)  is  placed  above,  and  slightly  posterior 
to  the  vestibular  district,  and  it  receives  its  name  from  the 
fact  that  it  lies  immediately  anterior  to  the  middle  meatus. 


396 


HEAD  AND  NECK 


It  is  slightly  hollowed  out  and  concave,  and  at  its  upper  part, 
near  the  nasal  bone,  a  feeble  elevation  termed  the  agger  nasi 
may  be  noticed ;  this  begins  close  to  the  anterior  part  of  the 
attached  margin  of  the  middle   concha,  and  runs  obliquely 


Fig.  155. — Lateral  Wall  of  the  Left  Nasal  Cavity.      (From  Schwalbe. ) 


1.  Frontal  air  sinus. 

2.  Free  border  of  the  nasal  bone. 
Cribriform  plate  of  ethmoid. 
Sphenoidal  air  sinus. 
Vibrissae. 

6.  The  two  parts  of  the  vestibular  area. 
Elevation     intervening     between     the 

vestibular  district  and  the  atrium. 

8.  Atrium  meatus  medii. 

9.  Agger  nasi,  or  rudiment  of  an  anterior 

concha. 
10.   Concha  suprema. 


3- 
4- 
5- 
6', 
7- 


11.  Recessus  spheno-ethmoidalis. 

12.  Superior  concha. 

13.  Superior  meatus. 

14.  Middle  concha. 

15.  Inferior  concha. 

16.  Plica  naso-pharjmgea. 

17.  Meatus  naso-pharyngeus. 

18.  Orifice  of  auditory  tube. 

19.  Posterior  lip  of  auditory  tube. 

20.  Lateral  recess  of  pharynx. 

21.  Incisive  foramen. 

«,  i5,  c.   Free  border  of  the  middle  concha. 


downwards  and  anteriorly.  It  represents  an  additional  concha 
which  is  present  in  some  mammals.  A  slight  depression 
above  the  agger  nasi,  which  leads  posteriorly  to  the  olfactory 
district  of  the  lateral  wall  of  the  nasal  cavity,  is  the  sulcus 
olfadorius. 

Conchse  (O.T.  turbinal  bones). — Posterior  to  the  vestibule 


NASAL  CAVITIES  397 

and  the  atrium  are  the  conchse  with  the  intervening  meatuses. 
The  superior  concha  (Fig.  155,  12),  which  projects  from  the 
labyrinth  of  the  ethmoid  bone,  is  very  short,  and  is  placed 
on  the  upper  and  posterior  part  of  the  lateral  wall  of  the 
cavity.  Its  free  border  begins  a  short  distance  below  the 
centre  of  the  cribriform  plate,  and  passes  obliquely  down- 
wards and  posteriorly  to  a  point  immediately  below  the 
body  of  the  sphenoid,  where  it  ends.  The  7?iiddle  concha 
(Fig.  155,  14)  also  is  a  part  of  the  ethmoid.  Its  free  border 
begins  a  short  distance  below  the  anterior  end  of  the  cribri- 
form plate,  and  at  first  takes  a  vertical  course  downwards  ;  then, 
bending  suddenly,  it  passes  posteriorly,  and  it  ends  midway 
between  the  body  of  the  sphenoid  and  the  posterior  border 
of  the  hard  palate.  The  inferior  concha  (Fig.  155,  15)  is  an 
independent  bone ;  it  extends  posteriorly  upon  the  lateral 
wall  of  the  nasal  cavity,  midway  between  the  middle  concha 
and  the  floor  of  the  nose.  Its  lower  free  margin  is  some- 
what convex  downwards. 

Meatus  Nasi. — The  superior  ineatus  (Fig.  155,  13)  is  a  short 
narrow  fissure  between  the  superior  and  middle  conchas. 
The  posterior  ethm.oidal  cells  open  into  its  upper  and  anterior 
part  by  one,  or,  in  some  cases,  by  several  apertures. 

To  bring  these  orifices  into  view,  the  superior  concha  should  be 
turned  aside  by  introducing  the  blade  of  a  pair  of  forceps  under  its  entire 
length,  and  forcing  it  upwards.  Care  should  be  taken  not  to  injure  the 
mucous  membrane  more  than  is  necessary. 

The  77iiddle  meatus  is  a  much  more  roomy  passage  which 
extends  posteriorly  from  the  atrium,  between  the  middle  and 
inferior  conchae. 

The  middle  concha  should  be  forcibly  tilted  upwards  and  posteriorly. 

The  upper  and  anterior  part  of  the  middle  meatus  leads  into 
a  funnel-shaped  passage  which  runs  upwards  into  the  corre- 
sponding frontal  sinus.  This  passage,  the  infu?idibulu?n,  con- 
stitutes the  channel  of  communication  between  the  frontal 
sinus  and  the  nasal  cavity. 

Upon  the  lateral  wall  of  the  middle  meatus  a  deep  curved 
groove  or  gutter,  which  commences  at  the  infundibulum  and 
runs  from  above  downwards  and  posteriorly,  will  be  seen. 
In  this  groove,  which  is  termed  the  hiatus  semilunaris  (Fig. 
156),   are  the  openings  of  the  anterior  ethmoidal    cells  and 


398 


HEAD  AND  NECK 


the  maxillary  sinus.  The  upper  boundary  of  the  hiatus 
semilunaris  is  prominent  and  bulging.  It  is  termed  the  bulla 
ethmoidalis.  On  or  above  the  bulla  is  the  aperture  of  the 
middle  ethmoidal  cells  (Fig.  156).  The  slit-like  opening  of 
the  maxillary  sinus  lies  in  the  posterior  part  of  the  hiatus 
semilunaris. 

The  dissector  should  now  open  up  the  maxillary  sinus  by  removing 
its  lateral  wall.  This  may  be  done  by  sawing  upwards  through  the  root  of 
the  zygomatic  process  of  the  maxilla. 

The  orifice  by  means  of  which  this  great  air  sinus  com- 


Orifice  of  anterior 
ethmoidal  cells 


Hiatus  semilunaris 

Atrium 

Orifice  of  maxil-       '■'''' 
lary  sinus 


Frontal  air-sinus 

Bulla  ethmoidalis 

Orifice  of  middle  ethmoidal  cells 

Orifices  of  posterior  ethmoidal  cells 

Recessus  spheno-ethmoidalis 
enoidal  sinus 


Cut  edge  of 
middle  concha 


Vestibule 


Orifice  of  naso-lacrimal  duct  _  1 

Inferior  meatus 


Middle  meatus 

Lateral  pharyn- 
geal recess 
Orifice  of 
auditory  tube 
Salpingo- 
pharyngeal fold 

Soft  palate 


Cut  edge  of  inferior 
concha 


Fig.  156. — Lateral  wall  of  Nasal  Cavity  and  Naso-pharynx.     The 
three  conchae  have  been  removed. 

municates  with  the  middle  meatus  Ues  in  the  medial  wall 
of  the  cavity  much  nearer  the  roof  than  the  floor — a  position 
highly  unfavourable  for  the  escape  of  fluids  which  may 
collect  in  it.  Sometimes,  however,  a  second  orifice,  circular 
in  outline,  wiU  be  found.  This  is  situated  lower  down  ;  when 
it  is  present  it  opens  into  the  middle  meatus,  immediately 
above  the  middle  point  of  the  attached  margin  of  the  inferior 
concha. 

The  dissector  should  note  that,  on  account  of  the  relationship  of  the 
infundibulum  to  the  hiatus  semilunaris  and  of  the  latter  to  the  opening 
of  the  maxillary  sinus,  there  is  a  tendency,  in  some  cases,  for  the  secretion 
of  the  frontal  sinuses  to  flow  into  the  maxillary  sinus. 


NASAL  CAVITIES  399 

The  inferior  meatus  is  the  horizontal  passage  which  Hes 
between  the  inferior  concha  and  the  floor  and  lateral  wall 
of  the  nasal  cavity.  It  is  placed  posterior  to  the  vestibule, 
and  the  free  border  of  the  inferior  concha  turns  downwards 
and  limits  it  anteriorly  (Fig.  156).  On  this  account,  and 
because  its  floor  slopes  downwards  and  posteriorly,  the  in- 
ferior meatus  is  more  accessible  to  the  current  of  expired 
air  than  to  the  current  of  inspired  air.  In  the  anterior  part 
of  this  meatus  will  be  found  the  opening  of  the  naso-lacrimal 
duct  which  conveys  the  tears  to  the  nasal  cavity  (Fig^  156). 

To  bring  the  aperture  of  the  naso-lacrimal  canal  into  view,  remove 
a  small  portion  of  the  anterior  part  of  the  inferior  concha  with  the 
scissors. 

The  orifice  of  the  naso-lacrimal  duct  varies  in  form, 
according  to  the  manner  in  which  the  mucous  membrane  is 
arranged  around  it.  Sometimes  it  is  wide,  patent,  and  circular  ; 
at  other  times  the  mucous  membrane  is  prolonged  over 
the  opening,  reducing  its  size  and  acting  as  a  flap  valve  to 
the  orifice.  In  some  cases,  indeed,  the  orifice  may  be  so 
minute  that  it  is  difficult  to  find.  Its  continuity  with 
the  lacrimal  sac  should  in  all  cases  be  established  by  passing 
a  probe  from  above  downwards  through  the  naso-lacrimal 
canal  (Fig.  64). 

K  fourth  meatus  is  generally  present  on  the  lateral  wall  of 
the  nasal  cavity.  This  is  due  to  the  partial  subdivision  of 
the  superior  concha  into  an  upper  and  lower  part  by  a  short 
groove  which  proceeds  anteriorly  from  the  anterior  aspect 
of  the  body  of  the  sphenoid.  This  additional  meatus  is 
termed  the  recessus  spheno-ethinoidalis^  and  in  its  posterior 
part  is  the  aperture  of  the  sphenoidal  air  sinus  (Fig.  156). 
This  orifice  may  be  circular  or  slit-like,  according  to  the 
manner  in  which  the  mucous  membrane  is  disposed  around 
it.^  The  upper  portion  of  the  superior  concha  which 
is  placed  above  this  additional  meatus  is  called  the  concha 
supre?na  (Fig.  155,  10). 

To  the  narrow  cleft-like  portion  of  the  nasal  cavity  which 
extends  from  the  roof  to  the  floor  between  the  septum 
medially  and  the  conchae  laterally  the  term  meatus  communis 
is  applied;  and  the  part  of  the  cavity  which  lies   posterior 

^  When  the  recessus  spheno-ethmoidalis  is  absent,  the  sphenoidal  air  sinus 
opens  into  the  interval  between  the  roof  of  the  nasal  cavity  and  the  superior 
concha. 


400  HEAD  AND  NECK 

to  the  conchal  region,  and  between  it  and  the  choanse, 
is  the  naso-pharyngeal  meatus  (Fig.  155,  17). 

Muco-periosteum  of  the  Lateral  Wall  of  the  Cavum  Nasi. 

— It  has  been  noted  that  the  vestibule  is  hned  with  integument. 
The  remainder  of  the  lateral  wall,  as  well  as  the  roof  and  floor 
of  the  nasal  fossa,  is  lined  with  mucous  membrane  which  is 
so  closely  blended  with  the  subjacent  periosteum  that  the 
two  are  inseparable  and  form  a  muco-periosteum.  This 
is  continuous  through  the  naso-lacrimal  duct  with  the  ocular 
conjunctiva,  through  the  various  apertures  with  the  delicate 
lining  membrane  of  the  air-cells  which  open  into  the  nasal 
cavity,  and  through  the  choanse  with  the  pharyngeal  mucous 
membrane.  On  the  lateral  wall,  as  on  the  septum,  the 
muco-periosteum  is  mapped  out  into  an  upper  olfactory  and 
a  lower  respiratory  portion.  This  subdivision  cannot  be 
appreciated  by  the  naked  eye,  for  the  one  district  passes 
into  the  other  without  any  sharp  line  of  demarcation.  The 
olfactory  region  comprises  merely  the  upper  concha;  the 
respiratory  region  includes  the  middle  and  inferior  conchse,  the 
middle  meatus,  the  lower  meatus,  and  the  atrium.  In  the  lower 
part  of  the  lateral  wall  the  muco-periosteum  is  thick  and 
spongy.  This  is  particularly  noticeable  over  the  lower  borders 
and  posterior  extremities  of  the  middle  and  inferior  conchse, 
where  the  membrane  presents  an  irregular  surface  and  forms 
soft  bulging  cushions.  This  condition  is  largely  due  to  the 
presence  of  a  rich  venous  plexus,  the  vessels  of  which  run 
for  the  most  part  in  an  antero-posterior  direction.  In  the 
case  of  the  lower  concha,  the  veins  are  so  numerous 
that  the  muco-periosteum  assumes  the  character  of  cavernous 
tissue,  and  is  sometimes  spoken  of  as  the  "erectile  body." 
When  turgid  with  blood  it  swells  out  and  obliterates  the 
interval  between  the  concha  and  the  septum.  The  muco- 
periosteum  of  the  floor,  meatuses,  and  the  atrium,  is 
smoother  than,  and.  not  so  thick  as,  that  over  the  conchse. 
Everywhere  numerous  mucous  glands  are  embedded  in  it, 
and  the  minute  punctiform  orifices  of  the  ducts  are  visible  to 
the  naked  eye.  In  the  olfactory  region  the  lining  membrane 
of  the  nose,  in  the  fresh  state,  is  of  a  yellowish  colour,  and 
it  is  softer  and  more  delicate  than  in  the  respiratory  part. 

The  great  vascularity  of  the  mucous  membrane  of  the  nose 
is  doubtless  for  the  purpose  of  moistening  and  raising  the 
temperature  of  the  inspired  air. 


NASAL  CAVITIES  401 

Nerves  and  Vessels  on  the  Lateral  Wall  of  the  Nasal 
Cavity  : — 

Nerves  of  Smell,    .     Olfactory  nerves. 

fi.   Lateral  nasal  branches  of  anterior  ethmoidal. 
2.   Nasal  branch  of  anterior  superior  alveolar. 
Nerves  of  Common  I  3.   Posterior    superior   nasal    branches    from    spheno- 
Sensation,   .        .  palatine  ganglion  and   from    the  nerve  of  the 

pterygoid  canal. 
^4.   Two    posterior   inferior  nasal  branches   from    the 
anterior  palatine  nerve. 

The  olfactory  nerves  are  from  twelve  to  twenty  fine  filaments 
which  spring  from  the  lower  surface  and  the  extremity  of  the 
olfactory  bulb,  and,  passing  through  the  apertures  in  the  cribri- 
form plate  of  the  ethmoid  into  the  nasal  cavity,  they  separate 
into  a  lateral  and  a  medial  group.  To  each  nerve  an  invest- 
ment from  the  cerebral  membranes  is  given.  The  medial  or 
septal  nerves  were  described  on  p.  392.  The  lateral  nerves 
descend  in  the  muco-periosteum  on  the  lateral  wall  of  the  nasal 
cavity.  At  first  lodged  in  shallow  grooves  or  minute  bony 
canals,  they  soon  divide  into  bunches  of  branches  which  spread 
out  over  the  upper  concha  and  the  region  immediately  below. 
The  dissection  of  these  nerves  is  exceedingly  difiicult,  but  in 
a  well-preserved  part  they  can  generally  be  partially  displayed. 

The  posterior  superior  nasal  nerves^  which  come  from  the 
spheno-palatine  ganglion  and  from  the  nerve  of  the  pterygoid 
canal,  are  minute  filaments,  but  the  dissector  should  nevertheless 
endeavour  to  trace  them  to  their  distribution  upon  the  lateral 
wall.  They  enter  the  nose  through  the  spheno-palatine  foramen, 
which  is  situated  at  the  posterior  end  of  the  superior  meatus. 

The  best  plan  to  adopt  for  their  display  is  to  trace  the  largest  of  the 
group,  the  naso-palatine  nerve,  which  has  already  been  exposed  on  the  nasal 
septum,  laterally  across  the  roof  of  the  nasal  cavity.  This  will  lead  the 
dissector  to  the  foramen,  and  by  carefully  dissecting  the  muco-periosteum 
in  its  neighbourhood  the  other  nerves  of  the  group  may  be  detected  as  they 
enter  the  nasal  cavity. 

They  are  distributed  to  the  muco-periosteum  over  the  upper 
and  middle  conchae,  and  the  posterior  part  of  the  septum. 

The  inferior  nasal  nerves  are  two  in  number ;  they  both 
arise  from  the  anterior  palatine  nerve. 

Make  a  vertical  incision,  through  the  muco-periosteum  over  the  posterior 
part  of  the  medial  pterygoid  lamina,  and  carefully  raise  the  membrane 
from  the  posterior  part  of  the  lateral  wall  of  the  nasal  cavity. 

The  upper  of  the  two  inferior  nasal  nerves  will  be  found 
emerging  through  a  small  aperture  in  the  perpendicular  part 
VOL.  II — 26 


402  HEAD  AND  NECK 

of  the  palate  bone,  at  a  point  between  the  posterior  extremities 
of  the  middle  and  inferior  conchse.  It  divides  into  an  ascend- 
ing and  descending  branch.  Both  run  anteriorly ;  the  former  on 
the  middle  concha,  the  latter  on  the  inferior  concha.  The  lower 
of  the  two  inferior  nasal  nerves  appears  through  a  foramen 
in  the  perpendicular  part  of  the  palate  bone,  immediately 
posterior  to  the  inferior  concha,  upon  which  it  is  distributed. 

The  anterior  ethmoidal  nerve  (O.T.  nasal)  should  be  ex- 
posed as  it  descends  in  the  groove  upon  the  deep  surface  of 
the  nasal  bone  (p.  393).  It  gives  medial  branches  to  the 
septum,  and  lateral  branches  to  the  muco-periosteum  over  the 
anterior  part  of  the  lateral  wall,  and  to  the  anterior  parts  of 
the  middle  and  inferior  conchse. 

The  main  artery  of  supply  to  the  nasal  muco-periosteum 
is  the  spheno-palatine,  a  branch  of  the  internal  maxillary.  It 
gains  entrance  to  the  nasal  cavity  through  the  spheno-palatine 
foramen,  in  company  with  the  posterior  superior  nasal  nerves. 
The  septal  branch  of  this  vessel  accompanies  the  naso-palatine 
nerve,  whilst  others  are  distributed  upon  the  lateral  wall  of  the 
cavity.  Several  twigs  are  given  also  by  the  descending  palatine 
branch  of  the  internal  maxillary  and  the  two  ethmoidal  arteries^ 
but  these  are  small  and  will  be  seen  only  in  cases  where  the 
injection  of  the  subject  has  been  unusually  successful. 


SPHENO-PALATINE  GANGLION  AND  INTERNAL 
MAXILLARY  ARTERY. 

The  spheno-palatine  ganglion  is  situated  in  the  pterygo- 
palatine fossa  on  the  lateral  side  of  the  spheno-palatine  fora- 
men ;  and  at  this  stage  it  can  be  exposed  best  by  dissecting 
from  the  medial  or  nasal  side. 

Dissection. — The  muco-periosteum  has  already  been  removed  from 
the  posterior  part  of  the  lateral  wall  of  the  nasal  cavity,  and  the  inferior 
nasal  branches  of  the  anterior  palatine  nerve  have  been  found  piercing  the 
perpendicular  part  of  the  palate  bone.  The  dissector  cannot  fail  to  notice 
the  course  taken  by  the  trunk  from  which  these  filaments  arise.  The  lamina 
of  bone  which  forms  the  medial  wall  of  the  pterygo-palatine  canal  is  so 
thin  that  the  nerve  can  be  distinctly  seen  through  it.  By  carefully  opening 
up  this  canal  with  a  chisel,  and  following  the  anterior  palatine  nerve  upwards, 
the  dissector  will  be  led  to  the  ganglion  in  the  pterygo-palatine  fossa. 
The  naso-palatine  nerve  should  at  the  same  time  be  traced  to  its  origin. 
The  ganglion  is  so  hemmed  in  by  the  bony  walls  of  the  fossa  that  it  is  very 
difficult  to  display  it  thoroughly  ;  but  by  removing  the  orbital  process  of  the 


SPHENOPALATINE  GANGLION  403 

palate  bone,  and  a  portion  of  the  body  of  the  sphenoid,  with  the  bone 
forceps,  it  may  be  more  or  less  satisfactorily  exposed.  In  the  same 
restricted  space  will  be  found  the  terminal  portion  of  the  internal  maxillary 
artery,  from  which  numerous  branches  are  given  off. 

Ganglion  Spheno-palatinum. — This  is  a  small,  triangular 
flattened  body,  which  is  lodged  in  the  pterygo-palatine  fossa. 
It  is  embedded  in  soft  fat,  and  is  surrounded  by  the  ter- 
minal branches  of  the  internal  maxillary  artery.  Two  stout 
spheno  -  palatine  branches  descend  from  the  maxillary  nerve 
and  join  it  from  above,  but  only  certain  of  their  fibres 
are  involved  in  the  ganglion  ;  the  remainder  are  continued 
directly  into  the  nasal  and  palatine  nerves  which  proceed 
from  the  ganglion.  The  spheno-palatine  branches  may  be 
regarded  as  constituting  the  sensory  roots  of  the  ganglion. 

From  the  spheno-palatine  ganglion  branches  are  given  off 
which  radiate  in  four  directions — viz.,  medially  to  the  nose ; 
downwards  to  the  palate ;  posteriorly  to  establish  connections 
with  the  facial  nerve  and  carotid  plexus,  as  wxll  as  to  supply 
the  mucous  membrane  of  the  pharynx ;  and  anteriorly  to  the 
orbit. 

Medial  branches,         .      Posterior  superior  nasal  nerves. 

r  Anterior  palatine. 
^  Descending  branches,   -  Middle  palatine. 

[Posterior  palatine. 

I  Nerve  of  pter\-goid  canal. 
Posterior  branches,     .  J  Some  lateral  posterior  superior  nasal 

[  branches. 

Anterior  branches,      .      Orbital. 

From  the  internal  maxillary  arter}'  twigs  are  given  off 
which  accompany  these  nerves. 

Posterior  Superior  JVasal  Nerves. — There  are  two  groups  of 
the  posterior  superior  nasal  nerves,  a  medial  and  a  lateral. 
The  medial  branches  pass  through  the  spheno  -  palatine 
foramen  and  across  the  roof  of  the  nasal  cavity  to  the  posterior 
part  of  the  septum.  The  largest  of  them,  the  naso-palatine 
nerve,  runs  downwards  and  anteriorly  in  a  groove  on  the 
surface  of  the  vomer  (p.  392).  Some  of  the  branches  of  the 
lateral  posterior  group  also  pass  through  the  spheno-palatine 
foramen  and  are  distributed  to  the  superior  meatus,  to  the 
superior  and  middle  conchae,  and  to  the  posterior  ethmoidal 
air  cells.  Other  branches  of  the  lateral  group  pass  posteriorly, 
some  in  the  muco-periosteum  of  the  upper  and  posterior  part 
of  the  nasal  cavity,  and  one  in  the  pharyngeal  canal  (O.T. 
II— 26  a 


404  HEAD  AND  NECK 

pterygo-palatine  or  pharyngeal  nerve).  They  are  distributed 
to  the  muco-periosteum  of  the  posterior  part  of  the  roof  of 
the  nasal  cavity,  to  the  adjacent  parts  of  the  wall  of  the 
pharynx,  to  the  sphenoidal  air  sinus,  and  to  the  pharyngeal 
part  of  the  auditory  tube. 

The  descending  branches  are  the  palatine  nerves,  and  with 
them  are  incorporated  the  posterior  inferior  nasal  nerves. 
The  palatine  nerves  are  three  in  number,  anterior  (O.T.  great 
or  posterior  palatine),  middle,  and  posterior.  As  a  rule  these 
spring  by  a  common  trunk  from  the  lower  aspect  of  the 
ganglion.  The  trunk  descends  in  the  pterygo-palatine  canal, 
which  has  been  opened  up  already,  but  to  expose  the 
nerves  a  dense  fibrous  investment  must  also  be  removed. 
The  nerve-trunk  will  then  be  seen  breaking  up  into  its  con- 
stituent parts. 

Dissection. — Trace,  in  the  first  instance,  the  two  smaller  nerves — viz., 
the  middle  and  posterior  palatine  branches.  These  leave  the  main  canal 
and  enter  the  small  palatine  canals,  which  conduct  them  through  the 
pyramidal  process  of  the  palate  bone.  Before  opening  these  up  it  is  well 
to  secure  the  nerves  as  they  emerge  from  the  lower  openings  of  the  canals. 
This  can  very  readily  be  done,  by  dissecting  posterior  to  the  hamulus  of 
the  medial  pterygoid  lamina  and  gently  separating  the  soft  parts  from 
the  under  aspect  of  the  pyramid  of  the  palate  bone.  As  the  dissection 
is  being  made  from  the  inside,  the  middle  palatine  nerve  will  be  first  en- 
countered, and  it  will  be  seen  to  pass  posteriorly  into  the  soft  palate, 
under  cover  of  the  tendinous  expansion  of  the  tensor  veli  palatini.^  This 
must  be  divided,  in  order  that  the  nerve  may  be  followed  to  its  distribu- 
tion. The  posterior  palatine  ne'f've  will  be  found  issuing  from  its  canal  a 
short  distance  to  the  lateral  side  of  the  preceding  nerve.  It  is  distributed 
to  the  soft  palate  in  the  neighbourhood  of  the  tonsil.  It  is  smaller  than 
the  middle  palatine  nerve,  and  is  sometimes  absent.  The  large  aiiterior 
palatine  nerve  should  now  be  followed  onwards  to  the  hard  palate.  To 
do  this  the  lower  part  of  the  palatine  canal  must  be  opened  up  by  removing 
a  small  portion  of  the  posterior  and  lateral  part  of  the  horizontal  plate  of 
the  palate  bone. 

The  anterior  palatine  nerve  is  the  largest  branch  of  the 
spheno-palatine  ganglion.  It  descends  through  the  pterygo- 
palatine canal,  accompanied  by  the  great  palatine  branch  of 
the  internal  maxillary  artery  ;  it  enters  the  palate  through  the 
great  palatine  foramen  and  runs  anteriorly,  in  a  groove  on  the 
lower  aspect  of  the  hard  palate,  towards  the  incisive  foramen. 
It  supplies  the  gum,  the  mucous  membrane,  and  the  glands 
of  the  vault  of  the  mouth ;  and,  in  the  neighbourhood  of  the 
incisive    foramen,  it   communicates    with    the    naso-palatine 

^  The  present  is  a  good  opportunity  to  observe  the  corrugated  or  wrinkled 
appearance  of  the  tendon  of  the  tensor  palati,  as  it  passes  under  the  hamulus. 


SPHENO-PALATINE  GANGLION  405 

nerve.  As  it  passes  down  the  pterygo- palatine  canal  the 
posterior  inferior  nasal  branches,  which  w^ere  enclosed  in 
its  sheath,  leave  it  and  enter  the  nasal  cavity  (p.  401). 

In  tracing  the  anterior  palatine  nerve  in  the  palate, 
the  dissector  should  note  the  numerous  glands  which  are 
placed  under  the  mucous  membrane  of  the  vault  of  the 
mouth,  and  the  manner  in  which  these  indent  the  bone.^ 

Dissection. — Considerable  difficulty  will  be  experienced  in  exposing  the 
nerves  in  the  pharyngeal  and  pterygoid  canals,  which  are  very  inaccessible. 

To  open  up  the  pharyngeal  canal  the  sphenoidal  process  of  the 
palate  bone  must  be  cautiously  removed  with  the  bone  forceps,  and  then 
the  dissector  should  proceed  to  open  up  the  pterygoid  canal  (O.T.  Vidian), 
which  traverses  the  root  of  the  pterygoid  process.  As  the  bone  is  very 
hard  and  brittle  at  this  point,  the  dissection  must  be  effected  very  carefully. 

The  nerve  of  the  pharyngeal  canal  belongs  to  the  posterior 
superior  nasal  group  (p.  403). 

Nerviis  Ca?ialis  Pterygoidel  (O.T.  Vidian).  —  The  nerve 
of  the  pterygoid  canal  is  formed  by  a  junction  between  the 
great  superficial  petrosal  branch  of  the  facial  and  the  great 
deep  petrosal  brajich  of  the  carotid  plexus.  It  traverses  the 
pterygoid  canal,  and  joins  the  posterior  aspect  of  the  spheno- 
palatine ganglion,  of  which  it  may  be  considered  to  repre- 
sent both  the  motor  and  sympathetic  root.  In  the  canal  it 
is  invested  by  a  strong  fibrous  envelope,  and  when  this  is 
removed  it  may  sometimes  be  noticed  to  break  up  into  a 
fine  plexus  which  surrounds  the  accompanying  artery.  It 
has  already  been  seen  to  give  some  fine  filaments  to  the 
muco-periosteum  of  the  nose. 

The  Rami  Orbitales. — The  orbital  branches  of  the  ganglion 
are  exceedingly  minute ;  they  pass  anteriorly  through  the 
inferior  orbital  fissure  to  supply  the  periosteum  of  the  orbit. 

Termination  of  Internal  Maxillary  Artery. — The  internal 
maxillary  artery  breaks  up  into  its  terminal  branches  in  the 
pterygo-palatine  fossa.     They  are — 

1.  Posterior  superior  alveolar  (p.  271). 

2.  The  infra-orbital  (p.  388). 

3.  The  descending  palatine. 

4.  The  spheno-palatine. 

The  Descending  Palatine  Artery. — The  descending  palatine 

^  An  equally  good  method  of  tracing  the  anterior  palatine  nerve  is  to 
remove  the  palatal  processes  of  the  palate  and  maxilla  with  the  bone 
forceps,  and  then  to  display  the  nerve  and  artery  on  the  upper  surfaces  of 
the  mucous  membrane  and  glands. 


4o6  HEAD  AND  NECK 

artery  is  a  terminal  branch  of  the  internal  maxillary  artery. 
As  it  descends  in  the  pterygo-palatine  fossa  it  gives  off,  usually, 
the  artery  of  the  pterygoid  canal,  and  as  it  enters  the  pterygo- 
palatine canal  several  small  palatine  arteries  spring  from  it ; 
then  it  becomes  the  great  palatine  artery.  The  great  palatine 
artery  descends  through  the  great  palatine  foramen  into  the 
hard  palate ;  there  it  runs  anteriorly  to  reach  the  incisive 
foramen,  through  which  it  passes  into  the  nasal  cavity  to 
anastomose  with  the  posterior  artery  of  the  septum,  which  is 
an  offset  of  the  spheno-palatine  artery. 

The  small  palatine  arteries^  which  spring  from  the  descend- 
ing palatine,  immediately  before  it  becomes  the  great  palatine 
artery,  in  the  upper  part  of  the  pterygo-palatine  canal ;  they 
descend  through  the  small  palatine  canals,  and  are  distributed 
to  the  soft  palate,  the  palatine  arches,  and  to  the  tonsil. 

The  Spheno-palatine  Artery. — The  spheno-palatine  artery 
enters  the  nasal  cavity  through  the  spheno-palatine  foramen. 
It  gives  off  (i)  a  branch  to  the  sphenoidal  air  sinus,  (2)  a 
branch  which  passes  posteriorly  to  the  upper  part  of  the 
pharynx  through  the  pharyngeal  canal  (O.T.  pterygo-palatine 
artery)  to  be  distributed  to  the  roof  of  the  posterior  part  of 
the  nasal  cavity  and  to  the  roof  of  the  pharynx ;  this  branch 
anastomoses  with  the  ascending  pharyngeal  artery.  Then  the 
spheno-palatine  artery  divides  into  lateral  and  septal  posterior 
nasal  branches.  The  lateral  branches  are  distributed  to  the 
lateral  wall  of  the  nasal  cavity,  where  they  anastomose  with 
the  branches  of  the  posterior  and  anterior  ethmoidal  arteries, 
and  with  the  lateral  nasal  branch  of  the  external  maxillary. 
They  supply  not  only  the  muco-periosteum  of  the  lateral 
wall  of  the  nasal  cavity,  but  also  the  muco-periosteum  of 
the  air  sinuses  which  open  into  the  cavity.  The  posterior 
septal  branch  of  the  spheno-palatine  artery  accompanies  the 
posterior  nasal  septal  nerve  along  the  surface  of  the  vomer ; 
it  anastomoses  with  the  great  palatine  artery,  and  with  the 
septal  branch  of  the  superior  labial  artery. 

THE  LARYNX. 

The  lateral  portions  of  the  mandible,  which  are  still 
attached  by  mucous  membrane  to  the  sides  of  the  tongue, 
should  be  removed,  and  the  dissection  of  the  larynx  com- 
menced. 


THE  LARYNX  407 

General  Construction  and  Position. — The  larynx  con- 
stitutes the  upper  expanded  portion  of  the  air-passage  which  is 
specially  modified  for  the  production  of  the  voice.  Its  walls 
are  composed  of  cartilages,  muscles,  ligaments,  and  an  in- 
ternal lining  of  mucous  membrane.  Before  proceeding  with 
the  dissection  the  student  should  study  the  form  and  con- 
nections of  the  nine  laryngeal  cartilages  in  a  permanent  speci- 
men {v.  p.  422). 

The  larynx  is  placed  in  the  upper  and  anterior  part  of 
the  neck,  where  it  forms  a  marked  projection.  It  lies  below 
the  hyoid  bone  and  tongue,  and  is  directly  continuous  with 
the  trachea  inferiorly.  Anteriorly  it  is  covered  by  the 
integument  and  fasciae,  and,  on  either  side  of  the  median 
plane,  by  two  thin  strata  of  muscles — viz.,  the  sterno-hyoid  and 
omo-hyoid ;  the  sterno-thyreoid  and  the  thyreo-hyoid.  As  a 
general  rule  a  narrow  process  of  the  thyreoid  gland,  termed 
the  pyra??udal  lobe,  is  also  continued  upwards  on  its  anterior 
surface.  On  each  side  the  lateral  lobe  of  the  thyreoid  gland  is 
prolonged  upwards  upon  it ;  and  it  is  related  to  the  great 
vessels  of  the  neck.  Posteriorly  it  is  in  relation  to  the  pharynx, 
which  separates  it  from  the  prevertebral  muscles.  If  the 
tip  of  the  epiglottis  is  taken  as  its  upper  limit,  the  larynx  in 
the  adult  may  be  regarded  as  being  placed  anterior  to  that 
portion  of  the  vertebral  column  which  extends  from  the  lower 
border  of  the  second  to  the  lower  border  of  the  sixth  cervical 
vertebra  ;  but  its  position  alters  somewhat  with  the  movements 
of  the  head  and  also  during  deglutition. 

Interior  of  tlie  Larynx. — The  cavity  of  the  larynx  is 
smaller  than  might  be  expected  from  an  inspection  of  its 
exterior.  On  looking  into  its  interior  from  above  it  wall  be 
seen  to  be  subdivided  into  three  portions  by  tw^o  elevated 
folds  of  mucous  membrane  which  extend  antero-posteriorly, 
and  project  inwards  from  each  side  of  the  cavity.  The  upper 
folds  are  termed  ihe  pliccs  veiitriadares  (O.T.  false  vocal  cords) ; 
the  lower  pair  receive  the  name  of  the  J>lic(E  vocales  (O.T. 
true  vocal  cords).  The  latter  are  the  chief  agents  in  the 
production  of  the  voice,  and  the  larynx  is  so  constructed 
that  changes  in  their  relative  position  and  in  their  degree  of 
tension  are  brought  about  by  the  action  of  the  muscles  and 
the  recoil  of  the  elastic  ligaments. 

Vestibulum  Laryngis. — The  vestibule  is  the  upper  sub- 
division of  the  laryngeal  cavity  (Fig.  150) ;  it  extends  from  the 


4o8 


HEAD  AND  NECK 


superior  aperture  {aditus  laryngls)  of  the  larynx  down  to  the 
pHcae  ventriculares.  In  its  lower  part  it  exhibits  a  marked 
lateral  compression.  Its  width,  therefore,  diminishes  from 
above  downwards,  whilst  owing  to  the  obliquity  of  the  aditus 
the  anterior  wall  is  longer  than  the  posterior.  Anteriorly  it 
is  bounded  by  the  posterior  surface  of  the  epiglottis  and  the 
thyreo-epiglottic  ligament,  both  covered  with  mucous  mem- 
brane. This  wall 
descends  obliquely 
from  above  down- 
wards and  anteri- 
orly, and  becomes 
narrower  as  it 
approaches  the 
anterior  ends  of  the 
plicae  ventriculares. 
Each  lateral  wall 
of  the  vestibule  is 
formed  by  the 
medial  surface  of 
the  ary-epiglottic 
fold.  For  the  most 
part  it  is  smooth 
and  slightly  con- 
cave, but  in  its 
posterior  part  the 
mucous  membrane 
bulges  medially  in 
the  form  of  two 
elongated  vertical 
elevations  placed 
one  posterior  to 
the  other.  The 
anterior  elevation  is  formed  by  the  cuneiform  cartilage  and 
a  mass  of  glands  associated  with  it,  enclosed  within  the 
ary-epiglottic  fold ;  the  posterior  elevation  is  due  to  the 
anterior  margin  of  the  aryttenoid  cartilage  and  the  cor- 
niculate  cartilage.  A  shallow  groove  descends  between  these 
rounded  elevations  and  terminates  below  by  running  into  the 
interval  between  the  ventricular  and  the  vocal  folds.  The 
posterior  wall  of  the  vestibule  is  narrow,  and  corresponds  to  the 
interval  between  the  upper  parts  of  the  two  arytaenoid  cartilages. 


Hyoid  bone 


Ary- 
epiglottic  fold 


Tubercle  of  epiglottis 


Thyreoid  cartilage   ''■  ~ 


Plica  ventricularis 
Ventricle  of  larynx 


Plica  vocalis 


Musculus  vocalis-' 


Cricoid  cartilage 


Fig.  157. — Frontal  section  through  the  Larynx 
to  show  the  Compartments. 


THE  LARYNX  409 

The  aditus  lary?igis  has  already  been  examined  in  the 
dissection  of  the  pharynx  (p.  378).  The  parts  which  bound 
it  should  again  be  carefully  studied. 

The  epiglottis  projects  upwards  posterior  to  the  root  of  the 
tongue.  Its  lingual  or  anterior  surface  is  free  in  the  upper 
part  of  its  extent  only,  and  is  attached  to  the  pharyngeal 
part  of  the  tongue  by  a  prominent  median  fold  of  mucous 
membrane,  termed  the  glosso-eplglottlc  fold.  Two  lateral  folds 
are  also  present;  they  connect  its  margins  with  the  lateral 
walls  of  the  pharynx  at  the  side  of  the  tongue  and  are 
called  iho.  pkaryngo-eplglottlc folds.  Between  the  two  layers  of 
mucous  membrane  which  constitute  each  of  these  three  folds, 
there  is  a  small  amount  of  elastic  tissue.  The  depression  on 
each  side  between  the  tongue  and  the  epiglottis  which  is 
bounded  by  the  glosso-epiglottic  and  the  pharyngo-epiglottic 
folds  is  termed  the  vallecula  (Fig.  150).  The  posterior  free 
surface  of  the  epiglottis  forms  the  greater  part  of  the  anterior 
boundary  of  the  vestibule  of  the  Jarynx.  The  upper  part  of 
this  surface  is  convex,  owing  to  the  manner  in  which  the 
upper  margin  is  curved  towards  the  tongue ;  below  this 
convexity  there  is  a  slight  concavity,  and  still  lower  a  marked 
bulging  over  the  upper  part  of  the  thyreo-epiglottic  ligament. 
This  last  projection  is  called  the  tubercle  of  the  epiglottis  \  it 
forms  a  conspicuous  object  in  laryngoscopic  examinations  of 
the  larynx. 

The  ary -epiglottic  folds  of  mucous  membrane  enclose 
between  their  two  layers  some  connective  tissue,  the  ary- 
epiglottic  muscles,  and,  posteriorly,  the  cuneiform  and  the 
corniculate  cartilages,  which  surmount  the  arytaenoid  cartilages. 
As  already  mentioned,  these  small  nodules  of  cartilage  raise 
the  posterior  part  of  the  ary-epiglottic  fold  in  the  form  of 
two  rounded  eminences  or  tubercles  which  are  easily  seen 
when  the  larynx  is  examined  by  the  laryngoscope. 

The  Middle  Subdivision  of  the  Laryngeal  Cavity  (Fig.  157) 
is  the  smallest  of  the  three.  Above  it  is  bounded  by  the 
ventricular  folds,  below  by  the  vocal  folds ;  it  communicates 
with  the  vestibule  above  and  the  inferior  compartment  of  the 
larynx  below. 

Plicce  Ventriculares  {O.T.  false  vocal  cords). — The  ventricular 
folds  are  two  prominent  mucous  folds  which  extend  antero- 
posteriorly  on  the  lateral  walls  of  the  laryngeal  cavity.  They 
are  soft   and  somewhat   flaccid,   and   their    free   borders  are 


4IO 


HEAD  AND  NECK 


slightly  arched,  with  the  concavities  looking  downwards. 
Within  each  fold  are  contained — (i)  a  ligamentum  ventriculare  ; 
(2)  numerous  glands  which  are  chiefly  aggregated  in  its  middle 
part;  and  (3)  a  few  muscle  fibres.  The  interval  between  the 
ventricular  folds  is  termed  the  rima  vestibuli  \  it  is  consider- 
ably wider  than  that  between  the  vocal  folds.  It  follows, 
therefore,  that  the  four  folds  are  distinctively  visible  when 
the  cavity  of  the  larynx  is  examined  from  above,  but  when 
examined  from  below,  the  vocal  folds  alone  can  be  seen. 

FUc(B  Vocales  (O.T.  True  vocal  cords).— ^\\&  vocal  folds  are 
placed  below  the  ventricular  folds,  and  extend  from  the  angle 
between  the  laminae  of  the  thyreoid  cartilage,  anteriorly,  to  the 


Base  of  tongue 


Glosso- 

epiglottic 

fold 

Epiglottis 
Tubercle 

Plica  vocalis 


Cuneiform  cartilage 


Corniculate  cartilage 


Fig.  158. — The  Larynx  as  seen  in  the  living  person  by  means  of  the 

Laryngoscope. 

vocal  processes  of  the  arytsenoid  cartilages  posteriorly.  Each 
vocal  fold  is  sharp  and  prominent,  and  its  mucous  membrane  is 
thin  and  is  firmly  bound  down  to  the  subjacent  vocal  ligament. 
In  colour  it  is  pale,  almost  pearly  white,  whilst  posteriorly 
the  point  of  the  vocal  process  of  the  arytaenoid  cartilage, 
which  stands  out  in  relief,  presents  a  yellowish  tinge.  In 
frontal  section  each  vocal  fold  is  somewhat  prismatic  in  form, 
and  the  free  border  looks  upwards  and  medially  (Fig.  157). 

The  vocal  folds  are  the  agents  by  means  of  which  the  voice 
is  produced.  The  ventricular  folds  are  of  little  importance 
in  this  respect ;  indeed,  they  can  in  great  part  be  destroyed 
without  any  appreciable  difference  in  the  voice  resulting. 

The  rima  glottidis  is  the  elongated  fissure  by  means  of 
which  the  middle  compartment  of  the  larynx  communicates 
with  the   lower   subdivision.     It   is   placed   somewhat   below 


THE  LARYNX 


411 


Hyo-epiglottic  ligament 


the  middle  of  the  laryngeal  cavity,  of  which  it  constitutes 
the  narrowest  part.  Anteriorly  it  corresponds  to  the  interval 
between  the  vocal  folds  ;  posteriorly  it  corresponds  to  the 
interval  between  the  bases  and  vocal  processes  of  the  ary- 
ta^noid  cartilages  (Fig.  160).  It  is  composed,  therefore,  of 
two  very  distinct  parts — (i)  a  narrow  anterior  portion,  be- 
tween the.  vocal  folds,  involving  less  than  two-thirds  of  its 
length,  and  called 
the      pars      inter-  ^    /Hyoid  bone 

viembranacea ;  (2)  a 
broader,  shorter  por- 
tion, between  the 
arytsenoid  cartilages, 
termed  the  pars  in- 
tercartilaginea.  The 
form  of  the  rima 
glottidis  undergoes 
frequent  alterations 
in  the  living  person. 
During  ordinary 
quiet  respiration  it  is 
lanceolate  in  outline, 
and  the  intermem- 
branous  part  has 
the  form  of  an  elon- 
gated triangle  with 
the  base  directed 
posteriorly.  When 
the  glottis  is  widely 
opened  the  broadest 
part  of  the  fissure 
lies  between  the  ex- 
tremities of  the  vocal 


age  of  epiglottis 
pad 
reo-hj'oid  membrane 

reoid  cartilage 
Elevation  produced  by 
cuneiform  cartilage 
entricular  fold 

Philtrum  ventriculi 
Elevation  produced 
byarytaenoid  cartilage 
Laryngeal  ventricle 

Vocal  fold 
Arytaenoid  muscle 

Processus  vocalis 

Cricoid  cartilage 
Cricoid  cartilage 


Fig.  159. — Median  section  through  the  Larynx 
to  show  the  Lateral  Wall  of  its  Right  Half. 


processes  of  the  arytaenoid  cartilages,  and  there  each  side 
of  the  rima  presents  a  marked  angle.  The  two  vocal  folds, 
on  the  other  hand,  may  be  approximated  so  closely  to  each 
other,  as  in  singing  a  high  note,  that  the  intermembranous 
part  is  reduced  to  a  linear  chink.  The  length  of  the  entire 
fissure  differs  considerably  in  the  two  sexes.  In  the  male 
its  average  length  is  23  mm.  ;  in  the  female,  17  mm. 

The  lateral  wall  of  the  larynx,  in  the  interval  between  the 
ventricular  and  the  vocal  folds,  shows  a  pocket-like  depression 


412 


HEAD  AND  NECK 


or  recess,  termed  the  ventriculus  laryngis  (O.T.  laryngeal 
sinus).  The  dissector  should  endeavour  to  gauge  the 
extent  of  this,  by  means  of  a  probe  bent  at  the  extremity. 
The  recess  passes  upwards,  undermining  the  ventricular  fold, 
and  its  mouth  or  orifice  is  narrower  than  its  cavity.  Under 
cover  of  the  anterior  part  of  the  ventricular  fold  a  slit-like 
aperture  will  be  detected.  This  leads  into  the  appendix 
ventriculi  (O.T.  laryngeal  saccule),  a  small  diverticulum,  which 
ascends    between    the    ventricular    fold    and    the    lamina    of 

Thyreoid  cartilage 

Vocal  ligament 

Rima  glotticlis 


Aryta^noid 
cartilage 


Vocal  process  of 
arytainoid  cartilage 


Fig.  i6o. — Diagram  of  the  rima  glottidis. 
A.  During  ordinary  easy  breathing.  B.  Widely  open. 

the  thyreoid  cartilage.  This  sac  is  of  variable  extent,  but 
as  a  rule  it  ends  blindly  at  the  level  of  the  upper  border  of 
the  thyreoid  cartilage. 

Distend    the    ventricle,    and,  if    possible,   the   appendix,    with    cotton 
wadding.     This  will  greatly  facilitate  the  subsequent  dissection. 

The  Lowest  Subdivision  of  the  Laryngeal  Cavity  (Fig.  157) 
leads  directly  downwards  into  the  trachea.  Above,  it  is 
narrow  and  laterally  compressed,  but  it  gradually  widens  out 
until  in  its  lowest  part  it  is  circular.  It  is  bounded  by  the 
sloping  inner  surface  of  the  conus  elasticus,  and  by  the  inner 


THE  LARYNX  413 

aspect  of  the  cricoid  cartilage.  It  is  through  the  anterior  wall 
of  this  compartment  that  the  opening  is  made  in  the  operation 
of  laryngotomy. 

Mucous  Membrane  of  the  Larynx. — This  is  continuous 
above  with  that  lining  the  pharynx,  and  below  with  the 
mucous  lining  of  the  trachea.  Over  the  laryngeal  or  posterior 
surface  of  the  epiglottis  it  is  closely  adherent,  but  elsewhere, 
above  the  level  of  the  vocal  folds,  it  is  loosely  attached  by 
submucous  tissue.  As  it  passes  over  the  vocal  folds  it  is  very 
thin  and  tightly  bound  down,  and  in  inflammatory  conditions 
of  the  larynx,  attended  by  cedema,  this  attachment  usually 
prevents  the  infiltration  of  the  submucous  tissue  from  extend- 
ing downwards  below  the  rima  glottidis. 

The  mucous  membrane  of  the  larynx  has  a  plentiful  supply 

of  racemose  glands  which  secrete  mucus.     Over  the  surface 

of  the  vocal  folds  these  are  completely  absent. 

Dissection. — Place  the  larynx  upon  a  block  so  that  its  anterior  surface 
looks  upwards,  and  fix  it  in  that  position  with  pins.  The  branches  which 
the  external  laryngeal  nerve  gives  to  the  crico-thyreoid  muscle  should  in  the 
first  place  be  followed  out ;  and,  carefully  preserving  the  superior  and  inferior 
laryngeal  vessels  and  the  internal  and  inferior  laryngeal  nerves,  the  dis- 
sector should  in  the  next  place  proceed  to  remove  the  thyreoid  gland,  and 
the  omo-hyoid,  sterno-hyoid,  sterno-thyreoid,  and  thyreo-hyoid  muscles. 
The  fibres  of  origin  of  the  inferior  constrictor  muscle  also  should  be 
cleared  away  from  the  thyreoid  and  cricoid  cartilages.  The  broad  thyreo- 
hyoid  membrane,  the  crico-thyreoid  ligament,  and  the  crico-thyreoid 
muscles  are  now  exposed,  and  their  attachments  may  be  defined. 

Membrana  Hyo-thyreoidea. — This  is  a  broad  membranous 
sheet,  which  occupies  the  interval  between  the  hyoid  bone 
and  the  thyreoid  cartilage.  It  is  not  equally  strong  throughout, 
but  shows  a  central  thick  portion,  the  median  thyreo-hyoid 
ligament,  largely  composed  of  elastic  fibres,  and  cord -like 
right  and  left  margins,  the  lateral  thyreo-hyoid  ligaments, 
whilst  in  the  intervals  between  the  central  part  and  the 
lateral  margins  it  is  thin  and  weak.  The  median  ligament  is 
attached  above  to  the  posterior  aspect  of  the  upper  margin  of 
the  body  of  the  hyoid  bone ;  below,  it  is  fixed  to  the  sides  of 
the  deep  median  notch  which  interrupts  the  superior  border  of 
the  thyreoid  cartilage.  The  upper  part  of  its  anterior  surface  is, 
therefore,  placed  posterior  to  the  posterior  hollowed-out  surface 
of  the  body  of  the  hyoid  bone ;  a  mucous  bursa  is  interposed 
between  them,  and  in  certain  movements  of  the  head  and 
larynx  the  upper  border  of  the  thyreoid  cartilage  is  allowed 
to  slip  upwards  posterior  to  the  hyoid  bone.     On  each  side  of 


414 


HEAD  AND  NECK 


Crico-thyreold  ligament 


Pars 

obliqua 


the  strong  central  part  the  thyreo-hyoid  membrane  is  attached 
below  to  the  upper  margin  of  the  lamina  of  the  thyreoid 
cartilage,  and  above  to  the  deep  aspect  of  the  great  cornu  of 
the  hyoid  bone.  It  is  pierced  by  the  internal  laryngeal  nerve 
and  superior  laryngeal  vessels.  The  lateral  thyreo-hyoid 
ligament,  which  forms  the  posterior  border  of  the  membrane, 
on  each  side,  is  rounded  and  cord-like,  and  is  composed  chiefly 
of  elastic  fibres.  It  extends  from  the  tip  of  the  great  cornu 
of  the  hyoid  bone  to  the  extremity  of  superior  cornu  of  the 
thyreoid  cartilage.      In  this  ligament  there  is  usually  developed 

a  small  oval  cartilaginous 
or  bony  nodule,  which  is 
termed  the  cartilago  triticea. 
Musculus  Crico- 
thyreoideus. — The  crico- 
thyreoid  muscle  is  placed 
on  the  side  of  the  cricoid 
cartilage,  and  bridges  over 
the  lateral  portion  of  the 
crico  -  thyreoid  interval. 
Taking  origin  from  the 
lower  border  and  outer 
surface  of  the  arch  of 
the  cricoid  cartilage,  its 
fibres  spread  out  in  an 
upward  and  posterior 
direction,  and  are  inserted 
into  the  inner  aspect  of 
the  lower  margin  of  the 
thyreoid  lamina,  and  also  into  the  anterior  border  of  its 
inferior  cornu.  As  a  general  rule,  it  is  divided  into  two  parts. 
The  anterior  or  oblique  part  is  composed  of  those  fibres  which 
are  attached  to  the  lamina  of  the  thyreoid  cartilage ;  the 
posterior  or  straight  part  is  formed  of  those  fibres  which  are 
inserted  into  the  inferior  cornu  of  the  thyreoid  cartilage.  It 
is  closely  associated  with  the  inferior  constrictor  muscle.  The 
crico-thyreoid  muscle  is  supplied  by  the  external  laryngeal 
branch  of  the  superior  laryngeal  nerve. 

Conus  Elasticus. — Extending  upwards,  from  the  upper 
border  of  the  anterior  and  lateral  parts  of  the  cricoid  cartilage 
to  the  thyreoid  and  arytaenoid  cartilages,  is  a  strong  elastic 
membrane,    the    conus   elasticus^    which    is    separable    into    a 


Fig.  i6i. — The  Crico-thyreoid  Muscle. 


THE  LARYNX  415 

median  and  two  lateral  parts.  The  median  part  is  the  crico- 
thyreoid  ligament  which  extends  from  the  upper  border  of  the 
anterior  part  of  the  cricoid  arch  to  the  lower  border  of  the 
thyreoid  cartilage.  Each  lateral  part  (O.T.  lateral  part  of 
crico-thyreoid  membrane)  runs  upwards  and  medially  and 
terminates  in  a  free  thickened  border,  the  ligamentu??i  vocale, 
which  lies  in  the  substance  of  the  plica  vocalis  and  is 
attached  posteriorly  to  the  vocal  process  of  arytaenoid,  and 
anteriorly  to  the  angle  of  union  of  the  two  laminae  of  the 
thyreoid  cartilage.  The  inner  surface  of  the  conus  eJasticus 
is  covered  with  the  mucous  membrane  of  the  lowest  section  of 
the  cavity  of  the  larynx,  and  the  outer  surface  is  in  relation 
with  the  lateral  crico-arytaenoid  and  the  vocalis  muscles. 

Dissection. — The  position  of  the  larynx  must  now  be  reversed.  Fix 
it  upon  the  block  in  such  a  manner  that  its  posterior  aspect  is  directed 
upwards.  The  oesophagus  should  then  be  slit  open  by  a  median  incision 
through  its  posterior  wall.  Next  remove  the  mucous  membrane  which 
covers  the  posterior  aspect  of  the  cricoid  and  arytaenoid  cartilages.  In 
doing  this,  bear  in  mind  that  the  inferior  laryngeal  artery  and  the  inferior 
laryngeal  nerve  pass  upwards,  between  the  thyreoid  and  cricoid  cartilages, 
and  must  be  preserved. 

Upon  the  posterior  aspect  of  the  broad  lamina  of  the  cricoid  cartilage 
the  dissector  will  now  note  the  two  posterior  crico-arytaenoid  muscles,  and 
the  attachment  of  the  tendinous  band  through  which  the  longitudinal  fibres 
of  the  oesophagus  are  fixed  to  the  cricoid  cartilage.  The  band  takes  origin 
from  the  prominent  median  ridge  on  the  posterior  aspect  of  the  cricoid 
cartilage.  On  the  posterior  surface  of  the  arytaenoid  cartilages,  and  bridg- 
ing across  the  interval  between  them,  are  the  transverse  and  oblique  parts 
of  the  arytaenoid  muscle.  Especial  care  must  be  taken  in  cleaning  this 
muscle  in  order  that  the  connections  of  the  superficial  decussating  fibres 
may  be  ascertained  fully. 

The  lateral  layer  of  the  right  ary-epiglottic  fold  of  mucous  membrane 
should  now  be  cautiously  removed.  This  will  expose  the  ary-epiglottic 
muscle,  the  cuneiform  cartilage,  and  the  corniculate  cartilage  of  that  side. 
This  is  perhaps  the  most  difficult  part  of  the  dissection,  because  the 
dissector  has  to  establish  the  continuity  of  the  sparse  fibres,  which  com- 
pose the  pale  ary-epiglottic  muscle,  with  the  decussating  fibres  of  the 
arytaenoid  muscle. 

Musculus  Crico-Arytsenoideus  Posterior. — The  posterior 
crico-arytaenoid  muscle  is  somewhat  fan-shaped  (Fig.  162). 
It  springs  by  a  broad  origin  from  the  depression  which  marks 
the  posterior  surface  of  the  cricoid  cartilage,  on  each  side  of 
the  median  ridge,  and  its  fibres  converge  to  be  inserted  into 
the  posterior  surface  of  the  muscular  process  or  projecting 
lateral  angle  of  the  base  of  the  arytaenoid  cartilage. 

In  pursuing  this  upward  and  lateral  course,  the  fibres  run  with  different 
degrees  of  obliquity.     The  uppermost  fibres  are  short  and  nearly  horizontal ; 


4i6 


HEAD  AND  NECK 


the  intermediate  fibres  are  the  longest,  and  are  very  oblique  ;  whilst  the 
lowest  fibres  are  almost  vertical  in  their  direction. 

Musculus  Arytsenoideus. — The  arytaenoid  muscle  consists 
of  two  portions — a  superficial  part,  termed  the  arytcenoideus 
obliquus^  and  a  deeper  layer,  called  the  arytcenoideus  iransversus. 

The  arytcenoideus  obliquus  is  composed  of  two  bundles  of 
muscular  fibres,  each  of  which  springs  from  the  posterior  aspect 
of   the   muscular    process    of    the    corresponding    arytenoid 


Epiglottis 

Great  cornu  of  hyoid 

Ary-epiglottic  fold 
Triticeal  cartilage 

Thyreo-hyoid  membrane. 

-Thyreoid  cartilage 

Union  of  oblique  arytsenoi- 
deus and  ary-epiglotticus 
Transverse  arj'taenoideus 

Crico-arj^aenoideus 
posterior 


Median  ridge  of  cricoid 
lamina 


Cartilage  ring  of  trachea 
Muscular  part  of  trachea 


Fig.  162. — Muscles  of  the  Posterior  Aspect  of  the  Larynx. 

cartilage  (Fig.  162).  From  these  points  the  two  fleshy  slips 
proceed  upwards  and  medially,  and  cross  each  other  in  the 
median  plane  like  the  limbs  of  the  letter  X.  Reaching  the 
summit  of  the  arytsenoid  cartilage  of  the  opposite  side,  some 
of  the  fibres  are  inserted  into  it,  but  the  greater  proportion 
are  prolonged,  round  the  base  of  the  corniculate  cartilage, 
into  the  ary-epiglottic  fold.  There  they  receive  the 
name  of  the  ary-epiglotticus  muscle^  and  as  they  approach 
the  epiglottis  they  are  joined  by  the  fibres  of  the  thyreo- 
epiglotticus  muscle.  The  oblique  arytaenoid  muscles  may 
be    considered    as    constituting    a   weak    sphincter    muscle 


THE  LARYNX 


417 


for  the  superior  aperture  of  the  larynx.  Each  bundle 
starting  from  the  base  of  one  of  the  arytaenoid  cartilages 
is  prolonged  into  the  ary- epiglottic  fold  of  the  opposite 
side,  and  along  this  to  the  margin  of  the  epiglottis. 

The  arytce?ioidens  transversus  is  an  unpaired  muscle.  It  is 
composed  of  transverse  fibres  which  bridge  across  the  interval 
between  the  two  arytaenoid  cartilages,  and  are  attached  to 
the  posterior  aspect  of  the  lateral  border  of  each  arytaenoid 
Many    of   the    fibres    turn    round    the    arytaenoid 


cartilage 


Epiglottis 
Small  cornu  of  hyoid  bone 

Body  of  hyoid  bone 


Lamina  of  thyreoid 
cartilage 

Musculus  vocalis 

Lateral  crico-arj^taenoid 

Posterior  crico-arytaenoid 

Crico-thyreoid  ligament 


Trachea 


Fig.  163. — Lateral  view  of  the  Muscles  of  the  Larynx.  The  fibres  passing 
postero-superiorly  from  the  upper  border  of  the  musculus  vocalis  are  the 
fibres  of  the  thyreo-epiglotticus.  1  hey  blend  above  with  the  ary- 
epiglotticus. 

cartilage  and  become  continuous,  on  each  side,  with  the  fibres 
of  the  thyreo-arytaenoid  muscle. 

Dissection. — The  further  dissection  of  the  larj-ngeal  muscles  should  be 
confined  to  the  right  side  of  the  larynx.  The  left  side  should  be  reserved 
for  the  study  of  the  nerves  and  vessels.  Place  the  larynx  on  its  left  side, 
and,  having  fixed  it  in  this  position,  remove  the  right  crico-thyreoid  muscle. 
The  right  lateral  part  of  the  thyreo-hyoid  membrane  should  next  be  divided, 
and  the  right  inferior  cornu  of  the  thyreoid  cartilage  disarticulated  from  its 
facet  on  the  side  of  the  cricoid  cartilage.  An  incision  should  now  be  made 
through  the  right  lamina  of  the  thyreoid  cartilage,  a  short  distance  to  the 

VOL.    II — 27 


41 8  HEAD  AND  NECK 

right  side  of  the  median  plane,  and  the  detached  piece  must  be  carefully 
removed.  Three  muscles  are  now  exposed,  and  must  be  cleaned. 
They  are  named  from  below  upwards  : — 

1.  The  lateral  crico-arytsenoid. 

2.  The  thyreo-arytaenoid. 

3.  The  thyreo-epiglotticus. 

Musculus  Cricoarytsenoideus  Lateralis. — The  lateral  crico- 
arytaenoid  muscle  is  triangular  in  form,  and  smaller  than  the 
posterior  crico-arytsenoid  (Fig.  163).  It  springs  from  the 
upper  border  of  the  lateral  part  of  the  cricoid  cartilage,  ex- 
tending to  the  facet  on  the  lamina  which  supports  the  base  of 
the  arytaenoid  cartilage ;  a  few  of  its  fibres  take  origin  from 
the  conus  elasticus  also.  From  this  attachment  its  fibres  run 
posteriorly  and  upwards,  and  converge  to  be  inserted  into  the 
anterior  surface  of  the  processus  muscularis  of  the  arytaenoid 
cartilage.  The  superficial  or  lateral  surface  of  this  muscle  is 
covered  by  the  lamina  of  the  thyreoid  cartilage  and  the  upper 
part  of  the  crico-thyreoid  muscle ;  its  deep  surface  is  applied 
to  the  conus  elasticus. 

Musculus  Vocalis. — The  musculus  vocalis  is  a  sheet  of 
muscular  fibres  which  springs,  anteriorly,  from  the  angle  of 
union  of  the  two  laminae  of  the  thyreoid  cartilage.  It  runs 
posteriorly,  along  the  ligamentum  vocale  and  the  upper  part 
of  the  conus  elasticus,  and  is  inserted  into  the  lateral  surface 
of  the  body  and  the  anterior  surface  of  the  muscular  process 
of  the  arytaenoid  cartilage.  Its  lower  fibres  blend  with  the 
upper  margin  of  the  lateral  crico-arytaenoid  muscle  and  the 
medial  fibres,  which  run  along  and  to  a  certain  extent  are 
attached  to  the  ligamentum  vocale,^  form  a  bundle,  triangular 
in  frontal  section,  to  which  the  term  internal  thyro-arytasnoid 
muscle  was  formerly  applied.  The  vocalis  muscle  protracts 
the  arytaenoid  cartilage,  and  adducts  and  relaxes  the  vocal 
ligaments. 

Musculus  Thyreoepiglotticus.  —  The  thyreo  -  epiglottic 
muscle  springs  from  the  thyreoid  cartilage,  immediately  above 
the  musculus  vocalis,  with  the  upper  border  of  which  it  is  more 
or  less  blended.  Its  fibres  run  posteriorly  and  upwards,  into 
the  ary-epiglottic  fold,  where  they  blend  with  the  ary-epiglot- 
ticus,  and  they  are  inserted  into  the  lateral  border  of  the 
lower  half  of  the  epiglottis. 

^  The  fibres   which   are  attached    to   the   ligamentum    vocale    are    called 
collectively  the  a?y-vocalis  muscle. 


THE  LARYNX 


419 


Musculus  Thyreoarytsenoideus  (O.T.  Thyro-arytenoideus 
Externus). — This  muscle  also  springs  from  the  angle  of  union 
of  the  two  laminae  of  the  thyreoid  cartilage,  in  close  associa- 
tion with  the  vocalis.  Its  fibres  pass  posteriorly,  and  are 
inserted  into  the  lateral  surface  of  the  arytaenoid  cartilage. 
It  protracts  the  arytsenoid  cartilage,  and  adducts  and  relaxes 
the  vocal  fold. 


Epiglottis  ---7 


Ary-epiglotticus-i^< 

Tubercle  of  epiglottis 

Ventricular  fold 

Ventricle  of  larynx 

Vocal  fold 

jMuscuIus  vocalis- 

Lateral  crico-arytsenoideus" 

Crico-thyreoid  muscle 

Cricoid  cartilage . 


Trachea  -i- 


FiG.  164. — Frontal  section  of  Larynx  showing  Muscles. 


Dissection. — The  lateral  crico-arytasnoid  muscle  should  now  be  carefully 
removed,  and  at  the  same  time  the  dissector  should  endeavour  to  disengage 
the  fibres  of  the  thyreo-arytsenoideus  from  the  deeper  musculus  vocalis, 
in  order  that  the  relation  of  the  latter  to  the  vocal  ligament  may  be 
studied.  Finally  remove  the  musculus  vocalis.  This  will  display  the  outer 
surface  of  the  conus  elasticus,  the  vocal  ligament,  and  the  wall  of  the  laryn- 
geal ventricle.  By  carefully  dissecting  between  the  two  layers  of  mucous 
membrane  which  form  the  ventricular  fold,  the  weak  ventricular  ligament, 
which  gives  it  support,  may  be  discovered,  as  well  as  a  number  of  racemose 
glands  which  lie  in  relation  to  it. 

Ligamentum  Vocale. — This  ligament  is  the  thickened 
free  border  of  the  lateral  part  of  the  conus  elasticus,  and  it 
constitutes  the  support  of  the  vocal  fold.  It  is  attached, 
anteriorly,  close  to  its  fellow  of  the  opposite  side,  to  the 
middle  of  the  angular  depression  between  the  two  laminae  of 


420 


HEAD  AND  NECK 


Muscular  process  of 
arytaenoid  cartilage 


the  thyreoid  cartilage.  From  this  it  stretches  posteriorly  to 
its  attachment  to  the  tip  and  upper  border  of  the  processus 
vocalis,  which  projects  anteriorly  from  the  base  of  the  arytsenoid 
cartilage.  The  vocal  ligament  is  composed  of  yellow  elastic 
fibres.  Its  medial  border  is  sharp  and  free  and  is  clothed 
with  mucous  membrane,  which  in  this  position  is  thin  and 
firmly  bound  down  to  the  ligament.  Embedded  in  its  anterior 
extremity  there  is  a  minute  nodule  of  condensed  elastic  tissue, 

called  the  sesamoid 

Arytaenoid  cartilage  Cartilage. 

By  removing 
the  mucous  mem- 
brane which  lines 
the  bottom  of  the 
laryngeal  ventricle 
the  dissector  will 
obtain  a  good  view 
of  the  parts  which 
bound  the  rima 
glottidis — viz.,  an- 
teriorly^ the  angle 
of  the  thyreoid 
cartilage;  pos- 
teriorly^ the  ary- 
tsenoideus  trans- 
versus  muscle ;  on 
each  side^  the  vocal 
ligament,  the  pro- 
cessus vocalis,  and 
the  medial  surface  of  the  arytaenoid  cartilage  (p.  i6o).  These 
parts  are  clothed  with  the  lining  mucous  membrane  of  the 
larynx. 

Ligamentum  Ventriculare. — This  feeble  band  supports  the 
ventricular  fold.  It  is  weak  and  indefinite,  but  somewhat 
longer  than  the  vocal  ligament.  Anteriorly,  it  is  attached  to 
the  angular  depression  between  the  two  laminae  of  the  thyreoid 
cartilage,  above  the  vocal  fold  and  immediately  below  the 
attachment  of  the  thyreo-epiglottic  ligament ;  and  it  extends 
posteriorly  to  a  tubercle  on  the  lateral  surface  of  the  arytaenoid 
cartilage  above  the  processus  vocalis.  It  is  composed  of  con- 
nective tissue  and  elastic  fibres,  which  are  continuous  with  the 
fibrous  tissue  in  the  ary-epiglottic  fold. 


Vocal  process  of 
arytaenoid  cartilage 


Rima  glottidis 


Vocal  ligament 
Lateral  part  of 
conus  elasticus 
Facet  for  inferior 
cornu  of  thyreoid 
cartilage 
Cricoid  cartilage 


Fig.  165. — Conus  elasticus.     The  right  lamina  of 
the  thyreoid  cartilage  has  been  removed. 


THE  LARYNX  421 

Dissedion.— Remove  the  remains  of  the  ary-epiglottic  fold,  the  ventricular 
and  the  vocal  folds,  and  the  lateral  part  of  the  conus  elasticus  on  the 
right  side  of  the  larynx,  but  be  careful  not  to  injure  the  arytx-noid  cartilage 
or'' the  corniculate  cartilage.  Should  the  cuneiform  cartilage  be  preseiit 
in  the  ary-epiglottic  fold  it  should  be  detached  and  preserved.  By  this 
dissection  a  closer  view  of  the  side  wall  of  the  laryngeal  cavity  can  be  ob- 
tained. The  undissected  vocal  fold  of  the  left  side  should  be  examined 
again,  the  laryngeal  ventricle  and  appendix  explored,  and  their  precise 
connections  and  extent  determined.  When  the  dissector  has  satisfied 
himself  upon  these  points  he  can  proceed  to  display  the  vessels  and  nerves 
of  the  larynx.  The  superior  laryngeal  artery  and  the  internal  laryngeal 
nerve  reach  the  pharynx  by  piercing  the  lateral  thin  part  of  the  thyreo-hyoid 
membrane,  and  they  descend  along  the  lateral  wall  of  the  recessus  piriformis 
to  the  larynx.  By  applying  traction  to  the  nerve,  and  at  the  same 
time  dividing  the  mucous  membrane  upon  the  medial  surface  of  the  thyreo- 
hyoid  membrane,  they  can  easily  be  discovered.  In  following  the  branches 
into  which  they  divide,  the  mucous  membrane  must  be  gradually  removed 
from  the  wall  of  the  larynx.  The  inferior  laryngeal  artery  and  nerve  enter 
from  below  and  proceed  upwards,  under  cover  of  the  lamina  of  the 
thyreoid  cartilage.  They  can  be  satisfactorily  displayed  only  by  the 
removal  of  this  piece  of  cartilage,  but  the  dissector  is  not  recommended 
to  adopt  this  method  unless  another  larynx  is  available  for  the  examination 
of  the  cartilages  and  joints.  By  drawing  the  thyreoid  cartilage  laterally 
the  more  important  branches  can  be  studied. 

Ramus    Internus  of  the   Nervus   Laryngeus   Superior. — 

In  the  dissection  of  the  neck  the  internal  laryngeal  nerve  was 
seen  springing  from  the  superior  laryngeal  branch  of  the 
vagus.  It  is  a  sensory  nerve,  and  its  branches  are  distributed 
chiefly  to  the  mucous  membrane  of  the  larynx.  After  pierc- 
ing the  lateral  part  of  the  thyreo-hyoid  membrane,  it  divides 
into  three  branches.  The  uppermost  of  these  sends  filaments 
to  the  ary-epiglottic  fold,  to  the  mucous  membrane  which 
covers  the  epiglottis,  and  to  the  three  folds  anterior  to  it. 
The  twigs  which  go  to  the  epiglottis  ramify  on  its  posterior 
surface,  but  many  of  them  pierce  the  cartilage  to  reach  the 
mucous  membrane  on  its  anterior  surface.  The  i7iter77iediate 
branch  of  the  internal  laryngeal  nerve  breaks  up  into  filaments, 
which  are  given  to  the  mucous  membrane  lining  the  side  wall 
of  the  larynx.  The  lowest  braiich  descends  and  gives  filaments 
to  the  mucous  membrane  which  covers  the  lateral  and 
posterior  aspects  of  the  arytaenoid  and  cricoid  cartilages.  A 
fairly  large  twig,  which  proceeds  from  this  branch,  runs  down- 
wards upon  the  posterior  aspect  of  the  cricoid  cartilage  to  join 
the  laryngeal  branch  of  the  recurrent  nerve. 

Nervus  Recurrens. — The  recurrent  nerve  has  previously 
been  seen  arising  from  the  vagus,  and  it  has  been  traced,  in 
the  neck,  up  to  the  point  where  it  disappears  under  cover  of 
II— 27  a 


42  2  HEAD  AND  NECK 

the  lower  border  of  the  inferior  constrictor  muscle  and  becomes 
the  inferior  laryngeal  nerve^  which  ascends  upon  the  lateral 
aspect  of  the  cricoid  cartilage,  immediately  posterior  to  the 
crico-thyreoid  joint.  There  it  is  joined  by  the  communicating 
twig  from  the  internal  laryngeal  nerve,  and  almost  immediately 
afterwards  it  divides  into  two  branches.  The  larger  of  the  two 
proceeds  upwards,  under  cover  of  the  lamina  of  the  thyreoid 
cartilage,  and  breaks  up  into  filaments  which  supply  the  lateral 
crico-arytsenoid,  the  thyreo-arytsenoid,  the  vocalis  and  the 
thyreo-epiglottic  muscles;  the  smaller  ox  posterior  branch  inclines 
upwards  and  posteriorly,  upon  the  posterior  aspect  of  the 
cricoid  cartilage,  and  under  cover  of  the  posterior  crico- 
arytsenoid  muscle.  It  supplies  twigs  to  that  muscle,  and  is 
then  continued  onwards  to  end  in  the  arytsenoid  muscles. 

The  inferior  laryngeal  nerve  is,  therefore,  the  motor  nerve 
of  the  larynx.  It  supplies  all  the  muscles  with  the  exception 
of  the  crico-thyreoid,  which  obtains  its  nerve-supply  from  the 
external  laryngeal.  The  inferior  laryngeal  nerve,  however, 
contains  a  few  sensory  fibres  also.  These  it  gives  to  the 
mucous  membrane  of  the  larynx  below  the  rima  glottidis. 

Laryngeal  Arteries.  —  The  superior  laryngeal  artery^  a 
branch  of  the  superior  thyreoid,  accompanies  the  internal 
laryngeal  nerve  ;  the  inferior  laryngeal  artery^  which  springs 
from  the  inferior  thyreoid,  accompanies  the  inferior  laryngeal 
nerve.  These  two  vessels  ramify  in  the  laryngeal  wall  and 
supply  the  mucous  membrane,  glands,  and  muscles. 

Laryngeal  Cartilages  and  Joints. — The  cartilages  which 
constitute  the  skeleton  of  the  larynx  and  give  support  to  its 
wall  are  the  following  : — 

\.  Scoid!'^'  1    .     ,  4.   Arytaenoid,      |      _ 

3.   Cartilage  of  the  r^^^g^^-  5-   Cormculate,        paired, 

epiglottis,         J  6-   Cuneiform,      J 

They  are  connected  by  certain  ligaments. 

Dissection.  —  The  mucous  membrane  and  muscles  must  be  carefully 
removed  from  the  cartilages,  and  the  ligaments  must  be  defined.  Great 
caution  must  be  exercised  in  cleaning  the  arytaenoid  cartilages  and  the 
corniculate  cartilages,  in  order  that  the  latter  may  not  be  injured. 

Cartilage  Epiglottica. — The  epiglottic  cartilage  is  a  thin, 
leaf-like  lamina  of  yellow  fibro-cartilage  which  is  placed  posterior 
to  the  tongue  and  the  body  of  the  hyoid  bone,  anterior  to 
the  upper  aperture  of  the  larynx.       When  divested  of  the 


THE  LARYNX  423 

mucous  membrane  which  covers  it  posteriorly  and  also,  to 
some  extent,  anteriorly,  the  epiglottic  cartilage  has  the  form 
of  an  obovate  leaf  and  is  indented  by  pits  and  pierced  by 
numerous  perforations.  In  the  pits  glands  are  lodged,  and 
through  the  foramina  vessels  and,  in  some  cases,  nerves 
pass.  The  broad  end  of  the  cartilage  is  directed  upwards 
and  is  free;  its  margins  are  to  a  large  extent  enclosed  within 
the  ary-epiglottic  folds.  The  anterior  surface  is  free  only  in 
its  upper  part.  This  part  is  covered  with  mucous  membrane 
and  looks  towards  the  base  of  the  tongue.  The  posterior 
surface  is  covered  throughout  its  whole  extent  with  the 
mucous  membrane  of  the  larynx.  The  pointed  lower  end 
of  the  cartilage,  the  petiolus,  is  connected  by  a  stout  fibrous 
band,  termed  the  thyreo-epiglottic  ligament,  to  the  angle 
between  the  laminae  of  the  thyreoid  cartilage. 

Epiglottic  Ligaments.  —  The  epiglottis  is  bound  by 
ligaments  to  the  base  of  the  tongue,  to  the  side  wall  of  the 
pharynx,  to  the  hyoid  bone,  and  to  the  thyreoid  cartilage. 
The  glosso-epiglottic  fold  and  the  two  pharyngo-epiglottic  folds 
have  been  studied  already.  In  each  there  is  a  small  quantity 
of  elastic  tissue.  The  hyo-epiglottic  Iiga7ne7it  is  a  short, 
broad  elastic  band  which  connects  the  anterior  face  of  the 
epiglottis  to  the  upper  border  of  the  body  of  the  hyoid  bone. 
The  thyreo-epiglottic  ligament  is  strong,  elastic,  and  thick.  It 
proceeds  downwards,  from  the  lower  pointed  extremity  of  the 
epiglottis,  and  is  attached  to  the  angular  depression  between  the 
two  laminae  of  the  thyreoid  cartilage,  below  the  median  notch. 

The  triangular  interval  which  is  left  between  the  lower 
part  of  the  cartilage  of  the  epiglottis  and  the  median  part  of 
the  thyreo-hyoid  membrane  contains  a  pad  of  soft  fat,  and  is 
imperfectly  closed  above  by  the  hyo-epiglottic  ligament. 

Cartilage  Thyreoidea.— This  is  the  largest  of  the  laryngeal 
cartilages.  It  is  composed  of  two  broad  and  somewhat  quadri- 
lateral plates,  termed  the  lamince,  which  meet  anteriorly  at  an 
angle,  and  become  fused  along  the  median  plane.  Posteriorly, 
the  lamina  diverge  from  each  other  and  enclose  a  wide 
angular  space.  The  anterior  borders  of  the  laminae  are  fused 
only  in  their  lower  parts.  Above  they  are  separated  by  a 
deep,  narrow  V-shaped  notch  called  the  incisiira  thyreoidea 
superior.  In  the  adult  male  the  angle  formed  by  the  meeting 
of  the  anterior  borders  of  the  two  laminae,  especially  in  the 
upper  part,  is  very  projecting ;  and,  with  the  margins  of  the 


424 


HEAD  AND  NECK 


superior  thyreoid  notch,  which  lies  above,  it  constitutes  a  marked 
subcutaneous  prominence  in  the  neck,  which  receives  the 
name  of  the  laryngeal  prominence  (O.T.  p07nu7n  Adanii).  The 
posterior  border  of  each  lamina  is  thick  and  rounded,  and  is 
prolonged  beyond  the  superior  and  inferior  borders  of  the 
lamina  in  the  form  of  two  slender  cylindrical  processes, 
termed   the    cornua.       The   superior  cornu^  longer   than  the 


Hyoid 


Epiglottis 


Cartilage  triticea. 

Thyreo-hyoid  membrane. 

Superior  cornu  of 
thyreoid  cartilage' 


Thyreoid  notch 

Prominentia  laryngea 
Crico-thyreoid  ligament 

Inferior  cornu  of  thyreoid 
Cricoid  cartilage 


Fig.  1 66. — Anterior  aspect  of  the  Cartilages  and  Ligaments  of  Larynx. 

inferior  cornu,  gives  attachment  to  the  lateral  thyreo-hyoid 
ligament.  The  shorter,  stronger  inferior  cornu  curves  slightly 
medially.  On  the  medial  aspect  of  its  tip  there  is  a  facet 
which  articulates  with  the  side  of  the  cricoid  cartilage.  The 
superior  border  of  the  lamina  is  for  the  most  part  slightly 
convex,  and  anteriorly  it  dips  down  to  become  continuous 
with  the  margin  of  the  superior  thyreoid  notch.  The  inferior 
border  is  to  all  intents  and  purposes  horizontal,  but  it  is 
divided  by  a  projection,   termed   the    inferior   tubercle^    into 


THE  LARYNX 


425 


Epiglottis 


—  Hyoid 


a  short  posterior  part  and  a  longer  anterior  part.  The  outer 
surface  of  the  lamina  is  relatively  flat.  Immediately  below 
the  posterior  part  of  the  upper  border,  and  anterior  to  the  root 
of  the  superior  cornu,  there  is  a  distinct  prominence  called  the 
superior  tubercle.  From  this  an  oblique  ridge  descends  towards 
the  inferior  tubercle  on  the  lower  border  of  the  lamina.  This 
ridge  gives  attachment  to  the  sterno-thyreoid,  thyreo-hyoid 
and  the  inferior 
constrictor  muscles, 
and  divides  the 
outer  surface  of  the 
lamina  into  an 
anterior  and  a  pos- 
terior part.  To  the 
latter,  which  is  much 
the  smaller  of  the 
two,  is  attached  the 
inferior  constrictor 
muscle  of  the 
pharynx.  The  inner 
surface  of  the  lamina 
is  smooth  and  slight- 
ly concave.  To  the 
angular  depression 
between  the  two 
laminae  are  attached 
the  thyreo-epiglottic 
ligament,  the  ven- 
tricular and  the  vocal 
ligaments. 

Crico-thyreoid 
Joints.  — The  articu- 
lation, on  each  side, 
between  the  tip  of  the  inferior  cornu  of  the  thyreoid  car- 
tilage and  the  side  of  the  cricoid  cartilage,  belongs  to  the 
diarthrodial  variety.  The  opposed  surfaces  are  surrounded 
by  a  capsular  ligament  which  is  lined  with  a  synovial  stratum. 
The  movements  which  take  place  at  these  joints  are  of  a 
twofold  character — viz.,  (i)  gliding;  (2)  rotatory.  In  the 
first  case  the  cricoid  facets  glide  upon  the  thyreoid  surfaces  in 
different  directions.  The  rotatory  movement  is  one  in  which 
the  cricoid  cartilage  rotates  around  a  transverse  axis  which 


Cartilage  triticea 

ThjTeo-hyoid 

membrane 


Superior  cornu 
of  the  thyreoid 
cartilage 


Superior  tubercle 


-  Oblique  line 
Inferior  tubercle 
Inferior  cornu 
Conus  elasticus 
Cricoid  cartilage 


Fig. 


167. — Profile  view  of  Cartilages  and 
Ligaments  of  Larvnx. 


426 


HEAD  AND  NECK 


passes  through  the  centre  of  the  two  joints.  Each  capsular 
ligament  is  strengthened  by  stout  bands  on  the  posterior 
aspect  of  the  joint. 

The  thyreoid  cartilage  should  now  be  removed  by  dividing  the  ligaments 
which  surround  the  crico-thyreoid  joint. 

Cartilage  Cricoidea. — This  is  shaped  like   a  signet  ring. 


Cartilage  triticea 

Thyreo-epiglottic 
ligament 


^rior  cornu 


orniculate  cartilage 

\rytaenoid 

Muscular  process 
of  arytaenoid 


Inferior  cornu 
of  thyreoid 


Fig.  168. — Posterior  aspect  of  Cartilages  and  Ligaments  of  Larynx. 

The  broad  posterior  part,  the  lamina^  is  somewhat  quadrilateral 
in  form.  Its  superior  border  presents  a  faintly  marked 
median  notch,  and  on  each  side  of  this  there  is  an  oval 
convex  facet  which  articulates  with  the  base  of  the  arytaenoid 
cartilage.  The  posterior  surface  of  the  lamina  is  divided,  by 
an  elevated  median  ridge,  into  two  slightly  hollowed -out 
areas  which  give  attachment  to  the  posterior  crico-arytaenoid 
muscles.     The  median  ridge  itself  gives  origin  to  a  tendinous 


THE  LARYNX  427 

band  which  proceeds  upwards  from  the  longitudinal  fibres  of 
the  oesophagus.  The  anterior  part  of  the  cricoid  cartilage 
is  the  arch.  The  lower  border  of  this  is  horizontal,  and  is 
connected  to  the  first  tracheal  ring  by  membrane,  the  crico- 
tracheal  ligame?tt.  The  arch  is  narrow  anteriorly,  and  is 
attached  to  the  lower  border  of  the  thyreoid  cartilage  by 
the  crico- thyreoid  ligament.  Posteriorly,  the  upper  border 
rapidly  ascends.  Upon  the  posterior  part  of  the  lateral 
surface  of  the  cricoid  cartilage  there  is  a  circular,  slightly 
elevated,  convex  facet,  which  looks  laterally  and  upwards,  for 
articulation  with  the  inferior  cornu  of  the  thyreoid  cartilage. 
Internally  the  cricoid  cartilage  is  lined  with  mucous  membrane, 
and  its  lumen  is  circular  below,  but  elliptical  above. 

The  narrow  band-like  part  of  the  anterior  arch  of  the 
cricoid  cartilage  lies  below  the  lower  border  of  the  thyreoid 
cartilage,  whilst  the  lamina  is  received  into  the  interval 
between  the  posterior  portions  of  the  laminae  of  the 
thyreoid  cartilage. 

Cartilagines  Corniculatse. — Before  proceeding  to  the  study 
of  the  arytaenoid  cartilages  the  dissector  should  examine  the 
corniculate  cartilages  and  the  manner  in  which  they  are 
held  in  position.  They  are  two  minute  pyramidal  nodules 
of  yellow  elastic  cartilage  which  are  placed  on  the  summits 
of  the  arytaenoid  cartilages,  and  are  directed  posteriorly  and 
medially.  Each  corniculate  cartilage  is  enclosed  within  the 
corresponding  ary-epiglottic  fold  of  mucous  membrane,  and 
is  joined  to  the  apex  of  the  arytaenoid  cartilage  by  a 
synchondrodial  joint. 

Cartilagines  Arytaenoideae. — In  dealing  with  the  arytaenoid 
cartilages  it  is  well  to  remove  one  in  order  that  its  external 
form  may  be  studied ;  the  other  should  be  retained  in 
position,  for  the  purpose  of  examining  the  crico-arytaenoid 
joint  and  the  movements  which  can  be  performed  at  that 
articulation. 

The  arytcenoid  cartilages  are  pyramidal  in  form,  and  sur- 
mount the  upper  border  of  the  lamina  of  the  cricoid 
cartilage.  The  apex  of  each  is  directed  upwards,  and  is 
curved  postero-medially.  It  supports  the  corniculate  cartilage. 
Of  the  three  surfaces,  one  looks  medially,  towards  the  corre- 
sponding surface  of  the  opposite  cartilage,  from  which  it  is 
separated  by  a  narrow  interval ;  another  looks  posteriorly ; 
whilst    the    third    is    directed    antero-laterally.      The    medial 


428  HEAD  AND  NECK 

surface  is  narrow,  vertical,  and  even,  and  is  clothed  with 
mucous  membrane.  The  posterior  surface  is  concave ;  it 
lodges  and  gives  attachment  to  the  arytaenoideus  transversus 
muscle.  The  antero-lateral  surface  is  the  most  extensive  of 
the  three,  and  is  uneven  for  muscular  and  ligamentous  attach- 
ments. Upon  this  aspect  of  the  arytaenoid  cartilage  the 
musculus  vocalis  and  the  thyreo-arytaenoid  muscles  are  in- 
serted. The  surfaces  of  the  arytaenoid  cartilage  are  separated 
by  three  borders,  viz.,  an  anterior,  a  posterior,  and  a  lateral. 
The  lateral  border  is  the  longest,  and,  at  the  base  of  the 
cartilage,  it  is  prolonged  postero-laterally  in  the  form  of  a 
stout  prominent  angle  or  process,  termed  the  processus  muscu- 
laris.  It  gives  attachment  anteriorly  to  the  crico-arytaenoideus 
lateralis  muscle ;  and  posteriorly  to  the  crico-arytaenoideus 
posterior.  The  anterior  border  of  the  arytaenoid  cartilage  is 
prolonged  into  the  projecting  anterior  angle  of  the  base. 
This  is  called  the  processus  vocalis.  It  is  sharp  and  pointed, 
and  gives  attachment  to  the  vocal  ligament  (O.T.  true  vocal 
cord).  The  base  of  the  arytaenoid  cartilage  presents  an 
elongated  concave  facet,  on  its  under  aspect,  for  articulation 
with  the  upper  border  of  the  lamina  of  the  cricoid  cartilage. 

Crico- arytaenoid  Joints. — These  articulations  are  of  the 
diarthrodial  variety.  There  is  a  distinct  joint  cavity  sur- 
rounded by  a  capsular  ligament,  which  is  lined  with  a  synovial 
stratum.  The  cricoid  articular  surface  is  convex,  that  of 
the  arytaenoid  concave ;  both  are  elongated  in  form,  but  they 
are  placed  in  relation  to  each  other  so  that  the  long  axis  of 
the  one  intersects  or  crosses  that  of  the  other,  and  in  no 
position  of  the  joint  do  the  two  surfaces  accurately  coincide. 
The  movements  allowed  at  this  joint,  as  the  dissector  can 
readily  determine,  are  of  a  twofold  kind — (i)  glidings  by 
which  the  arytaenoid  is  carried  medially  or  laterally,  or,  in 
other  words,  a  movement  by  which  the  arytaenoid  advances 
towards  or  retreats  from  its  fellow;  (2)  rotatory^  by  which  the 
arytaenoid  cartilage  revolves  round  a  vertical  axis.  By  this 
movement  the  vocal  process  is  swung  laterally  or  medially,  so 
as  to  open  or  close  the  rima  glottidis. 

The  dissector  should  note  that  the  capsule  of  this  joint 
is  strengthened  posteriorly  by  a  strong  band  which  plays  a 
most  important  part  in  the  mechanism  of  the  articulation. 
It  restricts  movement  of  the  arytaenoid  cartilage. 

Cartilagines  Cuneiformes. — These  are  two  little  rod-shaped 


THE  TONGUE  429 

nodules  of  yellow  elastic  cartilage,  which  are  placed  one  in 
each  ary-epiglottic  fold  near  its  posterior  end.  They  are  not 
always  present. 

Action  of  the  Larjmgeal  Muscles.  — The  dissector  should  now  consider 
the  manner  in  which  the  muscles  of  the  larynx  operate  upon  the  vocal 
ligaments  in  the  production  of  the  voice.  Tension  of  the  vocal  cords  is  pro- 
duced by  the  contraction  of  the  crico-thyreoid  imiscles.  The  oblique  parts 
of  the  muscles  pull  the  upper  border  of  the  cricoid  cartilage  upwards, 
whilst  the  straight  portions,  through  their  insertions  into  the  inferior  cornua, 
draw  the  cricoid  cartilage  posteriorly,  thereby  increasing  the  distance 
between  the  angle  of  the  thyreoid  cartilage  and  the  vocal  processes  of  the 
arytcenoid  cartilages.  When  the  crico-thyreoid  muscles  cease  to  contract, 
the  relaxation  of  the  cords  is  brought  about  by  the  elasticity  of  the 
ligaments.  The  vocalis  and  the  thyreo-aryteenoideus  must  be  regarded 
as  antagonistic  to  the  crico-thyreoid  muscles.  When  they  contract  they 
approximate  the  angle  of  the  thyreoid  cartilage  to  the  arytenoid  cartilages, 
and  still  further  relax  the  cords,  and  when  they  cease  to  act,  the  elastic 
ligaments  of  the  larynx  again  bring  about  a  state  of  equilibrium. 

The  width  of  the  riina  glottidis  is  regulated  by  the  arytrenoideus  muscle, 
which  draws  together  the  arytaenoid  cartilages.  The  lateral  and  posterior 
crico-aryta^noid  muscles  also  modify  the  width  of  the  rima  glottidis.  When 
they  act  together  they  assist  the  arytcenoid  muscle  in  closing  the  glottis, 
but  when  they  act  independently  they  are  antagonistic  muscles.  Thus  the 
crico-arytcenoidei  posterioj'es,  by  drawing  the  muscular  processes  of  the 
aryteenoid  cartilages  postero-laterally,  swing  the  processus  vocales  and  the 
vocal  folds  laterally,  and  thus  open  the  rima.  The  crico-aiytitnoidei 
laterales  act  in  exactly  the  opposite  manner.  By  drawing  the  muscular 
processes  in  an  opposite  direction  they  close  the  rima. 

But  the  muscles  of  the  larynx  have  another  function  to  perform  besides 
that  of  vocahsation.  It  was  formerly  thought  that  the  superior  aperture 
of  the  larynx  was  closed,  during  deglutition,  by  the  folding  back  of  the 
epiglottis  ;  that  in  fact  the  epiglottis,  during  the  passage  of  the  bolus  of 
food,  was  applied  like  a  lid  over  the  entrance  to  the  vestibule  of  the  larynx. 
The  investigations  of  Prof.  Anderson  Stuart  have  shown  that  the  superior 
aperture  of  the  larynx  is  closed  during  swallowing  by  the  close  apposition 
and  the  forward  projection  of  the  two  arytienoid  cartilages,  which  are 
forced  against  the  tubercle  of  the  epiglottis.  The  muscles  chiefly  concerned 
in  this  movement  are  the  thyreo-aryt^noid  muscles  and  the  transverse 
arytcenoid  muscle.  These  muscles  form  a  true  sphincter  vestibuli.  The 
ary-epiglotticus  muscle  also  assists  in  the  closure. 


THE  TONGUE. 

The  tongue  is  a  muscular  organ  placed  on  the  floor  of 
the  mouth.  It  has  important  duties  to  perform  in  connection 
with  the  functions  of  mastication,  deglutition,  and  articulation. 
Moreover,  the  mucous  membrane  which  covers  it  is  specially 
modified,  in  certain  localities,  in  connection  with  the  peripheral 
terminations  of  the  nerves  of  taste.  The  root  of  the  tongue 
is  attached  to  the  hyoid  bone ;  the  pointed  anterior  extremity 


430  HEAD  AND  NECK 

is  free  ;  the  upper  border  of  the  base  forms  the  lower  boundary 
of  the  isthmus  faucium. 

Mucous  Membrane. — The  lingual  mucous  membrane  is 
a  part  of  the  general  mucous  lining  of  the  buccal  cavity. 
The  dorsum  of  the  tongue^  when  the  mouth  is  closed  and 
the  organ  is  at  rest,  is  strongly  arched  antero-posteriorly, 
and,  for  the  most  part,  is  moulded  into  the  vaulted  roof  of 
the  mouth.  The  tongue  consists  of  two  developmentally 
distinct  parts,  termed  oral  and  pharyngeal.  These  are 
marked  off  from  each  other,  even  in  the  adult,  by  a  V-shaped 
groove  called  the  sulcus  terminalis.  The  apex  of  this  sulcus 
points  posteriorly,  and  coincides  with  a  median  bhnd  pit 
which  receives  the  name  of  the  foramen  ccecum.  From  this 
the  two  limbs  of  the  sulcus  diverge  antero-laterally,  and  they 
reach  the  margins  of  the  tongue  at  the  attachments  of  the 
glosso-palatine  arches. 

The  oral  part  of  the  tongue,  by  its  upper  or  dorsal 
surface,  stands  in  relation  to  the  hard  palate,  and  to  some 
extent  to  the  anterior  part  of  the  soft  palate  also.  The 
pharyngeal  part  of  the  tongue  looks  posteriorly,  and  forms 
the  anterior  wall  of  the  oral  portion  of  the  pharynx.  In  its 
upper  part  it  is  related  to  the  soft  palate,  whilst  below  it  is 
intimately  related  to  the  epiglottis.  On  the  lateral  wall  of  the 
pharynx,  immediately  above  this  portion  of  the  tongue,  is 
the  tonsil. 

The  mucous  membrane  which  envelops  the  tongue 
presents  very  different  appearances  in  different  localities. 
That  portion  which  is  spread  over  the  pharyngeal  part  of 
the  tongue,  and  is  prolonged  upwards  over  the  surface  of 
the  tonsil,  is  smooth  and  somewhat  glossy  and  presents  no 
visible  papillae.  It  is  from  this  district  that  the  glosso- 
epiglottic  fold  takes  origin,  and  every  here  and  there  the 
surface  is  studded  with  low  projections,  which  are  produced 
by  lymph  follicles  placed  subjacent  to  the  mucous  membrane. 
Each  of  these  small  elevated  areas,  as  a  rule,  presents  in  the 
centre  a  minute  pit,  visible  to  the  naked  eye. 

Anterior  to  the  foramen  caecum  and  sulcus  terminalis  the 
mucous  membrane  which  covers  the  dorsum,  sides,  and  tip 
of  the  oral  part  of  the  tongue  is  beset  with  papillae  of 
different  kinds.  As  these  are  individually  visible  to  the  naked 
eye  the  mucous  membrane  presents  a  very  characteristic 
appearance.      Further,  a  median  groove    or    sulcus   extends 


THE  TONGUE 


43 


posteriorly  from  the  tip  of  the  tongue  to  the  foramen  caecum, 
and  divides  the  anterior  two-thirds  of  the  dorsum  into  two 
halves. 

On  the  under  surface  of  the  tongue  the  mucous  mem- 
brane is  smooth  and  comparatively  thin.  In  the  median 
plane  it  forms  th.Q  frenulu?n  linguce^  which  has  been  studied 
at  an  earlier  stage.  On  either  side  of  the  median  line  the 
deep  lingual  vein  may  be  noticed,  in  the  living  subject,  ex- 
tending anteriorly  towards  the  tip.     To  the  lateral  side  of  this, 


Tip  of  tongue, 
turned  up 


Deep  lingual  vein 


Orifice  of- 
submaxillary  duct 


Frenulum  linguae 
Plica  fimbriata 

Plica  sublingualis 


Fig,  169. — The  Sublingual  Region  in  the  interior  of  the  mouth. 


and,  therefore,  somewhat  nearer  the  border  of  the  tongue,  is  a 
delicate  and  feebly  marked  fold  of  mucous  membrane,  from 
the  free  border  of  which  a  row  of  fringe-like  processes  or 
fimbriae  project.  It  is  termed  th.&  plica  fi?nbriata  ;  as  it  extends 
anteriorly,  towards  the  tip  of  the  tongue,  it  inclines  towards 
the  median  plane.  On  the  side  of  the  tongue,  immediately 
anterior  to  the  Hngual  attachment  of  the  glosso -palatine 
arches,  five  short  vertical  fissures  in  the  mucous  membrane, 
separated  by  intervening  folds,  may  be  noticed.  These  are 
th.Q  papillce  foltafcE.  They  are  the  representatives  of  leaf-like 
folds  of  the  mucous  membrane,  which  are  much  more  highly 
developed  in  certain  of  the  lower  animals  (hare  and  rabbit). 


432  HEAD  AND  NECK 

and  which  are  specially  concerned  in  receiving  the  impressions 
of  taste. 

Papillae  Linguales. — These  are  of  four  kinds,  and  differ 
in  size,  shape,  and  in  the  position  they  occupy  on  the 
surface  of  the  tongue.  They  are  termed  the  vallate,  the 
fungiform,  the  conical,  and  the  filiform. 

Fapillce  Vallatce. — The  vallate  papillae  (O.T.  circumvallate), 
seven  to  twelve  in  number,  are  the  largest,  and  are  placed 
immediately  anterior  to  the  sulcus  terminalis,  in  two  rows 
which  diverge  from  each  other  in  an  antero-lateral  direction, 
like  the  two  limbs  of  the  letter  V.  The  foramen  caecum 
lies  immediately  posterior  to  the  median  vallate  papilla,  which 
forms  the  apex  of  the  V.  In  form,  a  vallate  papilla  is 
broad  and  somewhat  cylindrical,  slightly  narrower  at  its 
attached  than  at  its  free  extremity,  and  it  is  sunk  in  a  pit. 
It  is  thus  surrounded  by  a  deep  trench,  the  outer  wall  of 
which,  termed  the  vallum^  is  slightly  raised  beyond  the  general 
surface  of  the  mucous  membrane,  and  forms  an  annular  eleva- 
tion which  encircles  the  free  extremity  or  summit  of  the 
papilla. 

Papillce  Fungiformes. — The  fungiform  papillae  are  much 
smaller,  but  are  present  in  much  greater  numbers.  They  are 
found  chiefly  on  the  tip  and  sides  of  the  tongue,  but  they  are 
scattered  at  irregular  intervals  over  the  dorsum  also.  Each 
papilla  presents  a  large,  full,  rounded,  knob-like  extremity, 
while  it  is  greatly  constricted  at  the  point  where  it  springs 
from  the  mucous  surface.  In  the  living  tongue  the  fungiform 
papillae  are  distinguished  by  their  bright  red  colour. 

PapillcB  ConiccE. — The  conical  papilla  are  present  in  very 
large  numbers.  They  are  smaller  than  the  fungiform  variety, 
and  although  they  are  quite  visible  to  the  naked  eye  they 
can  be  more  conveniently  studied  by  the  aid  of  an  ordinary 
pocket  lens.  They  are  minute  conical  projections  which 
taper  towards  their  free  extremities,  and  they  occupy  the 
dorsum  and  sides  of  the  tongue  anterior  to  the  sulcus 
terminalis.  They  are  arranged  in  parallel  rows  which  are 
placed  close  together,  and  in  the  posterior  part  of  the  dorsum 
these  diverge  from  the  median  sulcus  in  an  antero-lateral 
direction.  Towards  the  tip  of  the  tongue  the  rows  of  conical 
papillae  become  more  or  less  transverse  in  direction,  and  on 
the  sides  of  the  tongue  they  are  arranged  perpendicularly. 

PapillcE   Flliformes. — The   filiform   papillae  are   similar   in 


thp:  tongue 


433 


general  characters  to  the  conical  papillae,  but  the  epithelial 
cap  at  the  apex  of  the  cone  is  broken  up  into  thread-hke 
processes. 

Muscles  of  the  Tongue. — The  tongue  is  composed  almost 
entirely  of  muscular  fibres,  with  some  adipose  tissue  inter- 
mixed. It  is  divided  into  two  lateral  halves  by  a  median 
septum,   and  the  muscles  in  connection  with  each  of  these 


Posterior  belly' 
of  digastric 


Anterior  belly  of  digastric  JMylo-hyoid         Genio-hyoid 

Fig.  170. — Muscles  of  the  Tongue.      (From  Gegenbaur. ) 

consist  of  an  intrinsic  and  an  extrinsic  group.      They  are  as 
follows  : — 


\i 


Genio-glossus. 
Hyo-glossus. 


Extrinsic  Muscles,    -<   3.   Chondro-glossus 


Intrinsic  Muscles, 


4.  Stylo-glossus. 

I  5.  Palato-glossus. 

r  I.  Superior  longitudinal. 

I   2.  Inferi 

\Vt 


ferior  longitudinal. 

ertical. 

ransverse. 


The  extrinsic  muscles  take  origin  from  parts  outside  the 
tongue,  and  thus  are  capable  not  only  of  giving  rise  to  changes 
in  the  form  of  the  organ,  but  also  of  producing  changes  in 
its  position.  The  intrinsic  muscles^  which  are  placed  entirely 
within  the  substance  of  the  tongue,  are,  for  the  most  part, 
capable  of  giving  rise  to  alterations  in  its  form  only. 

VOL.  II — 28 


434  HEAD  AND  NECK 

With  the  exception  of  the  chondro-glossus,  the  extrinsic  muscles  have 
been  studied  already,  but  the  dissector  should  take  this  opportunity  of 
examining  more  fully  their  insertions,  and  the  manner  in  which  their  fibres 
are  related  to  one  another  and  to  those  of  the  intrinsic  muscles.  For  this 
purpose  carefully  reflect  the  mucous  membrane  from  the  right  half  of  the 
tongue,  and  follow  the  muscles  into  that  side  of  the  organ.  At  the  same 
time  the  lingual  nerve  and  the  profunda  linguae  artery  should  be  preserved. 
On  the  under  surface  of  the  tongue,  near  the  tip,  the  removal  of  the  mucous 
membrane  will  expose  a  group  of  glands,  aggregated  together  so  as  to  form 
a  small  oval  mass  on  each  side  of  the  median  plane.  This  is  known  as  the 
apical  gland  or  the  gland  of  Niihn, 

The  stylo-glossus  will  be  seen  running  along  the  side  of 
the  tongue  to  the  tip,  where  the  muscles  of  opposite  sides 
become  to  a  certain  extent  continuous.  The  hyo-glossus 
extends  upwards  to  the  side  of  the  tongue,  and  its  fibres  pass. 


Stylo-glossus 
Septum  linguae 
Inferior  longitudinal 
muscle 
Hyo-glossus 

Genio-glossus 

Fig.  171. — Transverse  section  through  the  posterior  part 
of  the  Tongue.      (From  Gegenbaur. ) 

for  the  most  part,  under  cover  of  those  of  the  stylo-glossus  to 
reach  the  dorsum,  over  the  posterior  part  of  which  they  spread 
out,  beneath  the  mucous  membrane.  The  genio-glossus  sends 
its  fibres  vertically  upwards  into  the  tongue  on  each  side  of 
the  median  septum,  and  its  insertion  stretches  from  the  tip 
to  the  base.  The  fibres  of  the  palato-glossus  become  con- 
tinuous with  those  which  form  the  stratum  transversum. 

The  cho)idro-glossus  is  not  always  present.  It  is  separated  from  the 
deep  surface  of  the  hyo-glossus  by  the  lingual  vessels,  and  by  the  pharyn- 
geal slip  of  the  genio-glossus.  It  is  a  slender  muscular  band  which  takes 
origin  from  the  medial  aspect  of  the  root  of  the  smaller  cornu,  and  the 
adjoining  part  of  the  body  of  the  hyoid  bone.  Its  fibres  ascend,  to  enter 
the  tongue  and  finally  spread  out  on  the  dorsum  under  cover  of  the 
superior  longitudinal  muscle. 

Musciilus  Longitudiiialis  Superior. — This  is  a  continuous 
layer  of  longitudinal  fibres  which  covers  the  entire  dorsum 
linguae,  from  the  root  to  the  tip,  immediately  beneath  the 
mucous  membrane.      Towards  the  base  of  the  tongue  it   is 


THE  TONGUE 


435 


thinner  than  in  front,  and  there  it  is  overlapped  by  the  trans- 
verse fibres  of  the  hyo-glossus,  and  is  intermixed  with  the 
fibres  of  the  chondro-glossus. 

Mtisculi  Longitudinahs  Inferiors.  —  The  inferior  longi- 
tudinal muscles  are  two  rounded  fleshy  bundles  placed  upon 
the  inferior  aspect  of  the  tongue,  one  on  each  side.  Pos- 
teriorly, each  inferior  longitudinal  muscle  lies  in  the  interval 
between  the  hyo-glossus  and  the  genio  -  glossus,  and  is 
attached  to  the  hyoid  bone;  anteriorly,  it  is  prolonged 
to  the  apex  of  the  tongue  between  the  medial  border  of 
the  stylo-glossus  and  the  genio-glossus ;  with  the  former  it  is 
more  or  less  blended. 

Musculus  Transversus  Lingua. — The  fibres  of  this  muscle 


Genio-glossus 

Genio-hyoid 


'^'^\         Superior  longitudinal 
muscle 

Lamellae  of 
transverse  muscle 


Inferior  longitudinal 
muscle 


Hyoid  bone 


Fig.  172. — Longitudinal  section  through  the  Tongue. 
(From  Aeby. ) 

lie  under  the  superior  longitudinal  fibres,  and  constitute  a 
thick  layer  which  extends  laterally  from  the  lateral  face  of 
the  septum  hnguae,  to  the  side  of  the  tongue.  The  fibres 
of  the  genio-glossus  ascend  through  this  transverse  stratum 
and  break  it  up  into  numerous  lamellEe  (Fig.  172).  It  is 
joined  by  the  fibres  of  the  palato-glossus  (Henle)  (Fig.  171). 

Musculus  Verticalis  Linguce. — The  vertical  fibres  extend  in 
a  curved  direction  from  the  dorsum  to  the  under  aspect  of 
the  tongue,  and  decussate  with  the  fibres  of  the  transverse 
muscle. 

Nerves  and  Vessels  of  tlie  Tongue. — The  nerves  of  the 
tongue  are— (i)  the  glosso-pharyngeal ;  (2)  the  lingual;  (3) 
the  hypoglossal;  and  (4)  a  few  twigs  from  the  internal 
laryngeal.  These  should  be  traced  on  the  left  side  of  the 
tongue,  where  the  mucous  membrane  is  still  in  position. 

The  glosso-pharyngeal  nerve  has  been  traced  up  to  the  point 


436 


HEAD  AND  NECK 


where  it  disappears  under  cover  of  the  hyo-glossus  muscle. 
There  it  divides  into  two  branches.  The  smaller  of  these 
extends  anteriorly,  upon  the  side  of  the  tongue,  and  may  be 
traced  as  far  as  a  point  midway  between  the  root  and  the  tip. 
The  larger  branch  turns  upwards,  and  is  distributed  to  the 
mucous  membrane  which  invests  the  posterior  third  of  the 
dorsum  linguae.  It  gives  twigs  to  the  vallate  papillae,  and 
some  fine  filaments  may  be  followed  to  the  anterior  surface 
of  the  epiglottis.  The  glosso-pharyngeal  nerve  is  a  nerve  of 
taste  and  of  common  sensibility. 

The  lingual  and  hypoglossal  nerves  are  described  on  pages 
289  and  316,  and  their  terminal  branches  should  now  be 
traced  as  far  as  is  possible. 

Superior  longi- 
tudinal muscle 


Transverse 
muscle" 


Stylo-glossus" 


Inferior  long 
tudinal  muscl 

Hyo-glossu 
Genio 


Fig.  173. 


Hyoid  bone         Genio-hyoid 
-Transverse  section  through  the  Tongue.      (From  Aeby. 


The  internal  laryngeal  nerve  gives  a  few  delicate  filaments 
to  the  glosso-epiglottic  and  pharyngo-epiglottic  folds  and  the 
mucous  membrane  of  the  root  of  the  tongue. 

The  arteria  profunda  lingua,  should  be  followed  to  the  tip 
of  the  tongue,  where  it  forms  a  small  loop  of  anastomosis  with 
its  fellow  of  the  opposite  side. 

Septum  Linguae. — The  septum  of  the  tongue  can  be  seen 
best  by  making  a  transverse  section  through  the  organ.  This 
will  display,  in  a  measure,  the  transverse  and  vertical  muscular 
fibres  also.  The  septum  is  a  median  fibrous  partition.  It 
is  strongest  posteriorly,  where  it  is  attached  to  the  hyoid 
bone.  It  does  not  reach  the  dorsum  of  the  tongue,  being 
separated  from  it  by  the  superior  longitudinal  muscle. 


GENERAL  APPEARANCE  OF  BRAIN  437 


ENCEPHALON— THE   BRAIN. 

Directiotis.  —  If  the  brain  was  divided  into  two  parts,  when  it  was 
removed,  they  should  be  fixed  together  with  large  pins  passed  through  the 
cerebellum  into  the  cerebral  hemispheres  ;  the  brain  should  then  be  placed 
on  a  dissecting-room  platter,  with  its  superior  surface  uppermost.  It  is 
necessary  to  keep  it  moist,  during  the  whole  dissection,  by  means  of  a 
cloth  dipped  in  water.  Unless  this  is  done  the  membranes  are  apt  to 
become  dry,  and  then  they  are  exceedingly  difficult  to  remove. 

General  Appearance  of  the  Brain. — When  viewed  from 
above,  the  brain  presents  an  ovoid  figure,  with  the  broad  end 
directed  posteriorly.  Its  greatest  transverse  diameter  is  in 
the  neighbourhood  of  the  part  which  lies  between  the  two 
parietal  tubers  of  the  cranium.  The  only  portions  which  are 
visible  when  the  brain  is  in  this  position  are  the  two  convoluted 
hemispheres  of  the  cerebrum.  These  are  separated  from  each 
other  by  a  deep  median  cleft,  called  the  longitudinal  fissure^ 
which  extends  from  the  anterior  to  the  posterior  end  of  the 
brain. 

The  position  of  the  brain  should  now  be  reversed.  Turn  it  so  that  it 
rests  on  its  superior  surface. 

The  inferior  aspect  of  the  brain  is  usually  termed  the 
"  base."  It  presents  an  uneven  and  irregular  surface,  which 
is  more  or  less  accurately  adapted  to  the  inequalities  on  the 
floor  of  the  cranium.  On  this  surface  the  main  subdivisions 
of  the  organ  may  be  recognised.  Thus,  posteriorly  is  seen  the 
short  cylindrical  portion,  called  the  7nedulla  oblongata^  through 
which,  at  the  foramen  magnum,  the  brain  becomes  continuous 
with  the  spinal  medulla.  The  medulla  oblongata  rests  on 
the  under  surface  of  the  cerebellum,  being  received  into  the 
vallecula  or  hollow  which  intervenes  between  the  two  cere- 
bellar hemispheres.  The  cerebellum  is  a  mass  of  considerable 
size  which  lies  under  the  posterior  parts  of  the  cerebral 
hemispheres.  It  can  be  easily  recognised  on  account  of  the 
closely  set,  curved  and  parallel  fissures  which  traverse  its 
surface.  Above  the  medulla  oblongata,  and  in  direct  connec- 
tion with  it,  is  a  prominent  white  elevation  called  the  pons. 
The  basilar  artery  extends  upwards  in  a  median  groove  on 
its  surface.  Immediately  anterior  to  the  pons  there  is  a 
deep  hollow  or  recess.  This  is  bounded  posteriorly  by  the 
11—28  a 


438 


THE  BRAIN 


pons,  on  either  side  by  the  projecting  temporal  lobes  of 
the  cerebrum,  and  anteriorly  by  the  orbital  portions  of  the 
frontal  lobes  of  the  cerebrum.     At  the  present  stage  of  the 


Optic  chlasma 


Infundibulum 


Corpora 
mamillaria 


Olfactory  bulb 


Substantia 


perforata     ■ 
posterior    mk 


Pedun- 

culus       If 
cerebri 


Olfactory  tract 


Optic  nerve 


Substantia  per- 
forata anterior 


Optic  tract 


Oculo-motor 
nerve 


Trigeminal 


Motor  root  of 
■facial  nerve 
.custic  nerve 

Sensory  root  of 
facial  nerve 

\Glosso-pharyngeal 
nerve 


Hypoglossal 
nerve 


Pyramid 


Vagus  nerve 
Accessory  nerve 

Hypoglossal  nerve 


Spinal  medulla  (cut) 
Fig.  i74._The  Base  of  the  Brain  with  the  Cerebral  Nerves  attached. 

examination  of  the  brain,  the  bottom  of  this  hollow  is  hidden 
from  view  by  the  arachnoid,  which  stretches  over  it  like  a 
veil  •  but  the  hypophysis  will  be  seen  within  its  limits  if  it  has 
been  removed'with  the  brain.  Passing  laterally  from  either 
side  of  the  anterior  part  of  this  recess  will  be  seen  the  deep 


MEMBRANES  AND  BLOOD  VESSELS  439 

fissura  lateralis  (O.T.  Sylvian  fissure),  which  intervenes  between 
the  pointed  and  projecting  extremity  of  the  temporal  lobe  and 
the  frontal  lobe  of  the  cerebrum ;  whilst  in  the  median  plane, 
anteriorly,  the  longitudinal  fissure  will  be  seen  between  the 
frontal  portions  of  the  cerebral  hemispheres.  On  either  side 
of  the  longitudinal  fissure,  and  separated  from  it  by  a  narrow 
gyrus,  the  olfactory  tract  and  bulb  may  be  recognised. 


MEMBRANES  AND  BLOOD  VESSELS  OF 
THE  BRAIN. 

Arachnoidea  Encephali. — The  arachnoid  forms  the  inter- 
mediate covering  of  the  brain.  It  is  placed  between  the  dura 
mater  and  the  pia  mater,  and  is  directly  continuous  w^ith  the 
arachnoid  of  the  spinal  medulla.  It  is  an  exceedingly  thin 
and  dehcate  membrane,  w^hich  can  be  seen  best  on  the  base 
of  the  brain,  as  in  that  locality  it  is  not  so  closely  applied  to 
the  pia  mater  as  elsewhere.  UnHke  the  pia  mater  it  does 
not  (except  in  the  case  of  the  longitudinal  and  the  lateral 
fissures)  dip  into  the  sulci  or  fissures  on  the  surface  of  the 
cerebrum  and  cerebellum.  It  bridges  over  the  inequalities  on 
the  surface  of  the  brain  and  it  is  spread  out  in  the  form  of  a 
very  distinct  sheet  over  the  medulla  oblongata,  the  pons,  and 
the  hollow  on  the  base  of  the  brain  which  lies  anterior  to  the 
pons.  The  cut  ends  of  several  of  the  cerebral  nerves  will  be 
seen  passing  through  this  sheet  \  whilst,  anteriorly,  immedi- 
ately to  the  lateral  side  of  the  optic  nerve,  the  internal  carotid 
artery  will  be  noticed  piercing  it. 

Cavum  Subarachnoideale. — The  interval  between  the  arach- 
noid and  the  pia  mater  receives  the  name  of  the  subarachnoid 
space.  It  contains  the  subarachnoid  fluid,  and  is  broken  up 
by  a  meshwork  of  fine  filaments  and  trabecule,  which  connects 
the  two  bounding  membranes  (viz.,  the  arachnoid  and  the  pia 
mater)  in  the  most  intimate  manner,  and  form  a  delicate 
sponge-like  interlacement  between  them.  Where  the  arach- 
noid passes  over  the  summit  of  a  cerebral  gyrus,  and  is  con- 
sequently closely  applied  to  the  subjacent  pia  mater,  the 
meshwork  is  so  close  and  the  trabeculse  so  short  that  the 
two  membranes  cannot  be  separated  from  each  other.  To 
the  dissector  they  appear  to  form  a  single  lamina.  In  the 
intervals  between  the  rounded  margins  of  adjacent  gyri  distinct 


440 


THE  BRAIN 


angular  spaces  exist  between  the  arachnoid  and  the  pia 
mater.  In  these  the  subarachnoid  tissue  can  be  studied,  and 
it  will  be  seen  that  these  intervals  on  the  surface  of  the 
cerebrum  serve  as  communicating  channels  for  the  free 
passage  of  the  subarachnoid  fluid  from  one  part  of  the  brain 
to  another.  The  larger  branches  of  the  arteries  and  veins 
of  the  brain  traverse  the  subarachnoid  space ;  their  walls  are 
directly  connected  with  the  subarachnoid  trabeculae  and  are 
bathed  by  the  subarachnoid  fluid. 

Cisternse    Subarachnoideales. — In   certain    situations    the 
arachnoid   is    separated  from   the   pia  mater   by  intervals  of 


Sub-arachnoid  space  and  trabeculae 


""""Dura  mater 
Subdural  space 
Arachnoid 
Pia  mater 


Fig.  175. — Diagrammatic  section  through  the  Meninges  of 
the  Brain.      (Schwalbe. ) 

CO.  Grey  matter  of  cerebral  gyri. 


considerable  depth  and  extent.  These  expansions  of  the 
subarachnoid  space  are  termed  cisternse  subarachnoideales.  In 
them  the  subarachnoid  tissue  is  relatively  reduced.  There 
is  no  longer  a  close  meshwork ;  the  trabeculae  connecting  the 
two  bounding  membranes  take  the  form  of  long  filamentous 
intersecting  threads  which  traverse  the  spaces.  A  beautiful 
demonstration  of  these  may  be  obtained  by  dividing  in  the 
median  plane,  with  the  scissors,  the  sheet  of  arachnoid  which 
is  spread  over  the  medulla  oblongata  and  pons,  and  turning 
the  two  pieces  gently  aside. 

Certain  of  the  cisternae  require  special  mention.  The  largest  and  most 
conspicuous  is  called  the  cisterna  cerebello-inedullaris  (O.T.  magna).  It  is 
a  direct  upward  continuation  of  the  posterior  part  of  the  subarachnoid  space 


MEMBRANES  AND  BLOOD  VESSELS 


441 


of  the  spinal  meninges  into  the  posterior  part  of  the  cranium.  It  is  formed 
by  the  arachnoid  membrane  bridging  over  the  wide  interval  between  the 
posterior  part  of  the  under  surface  of  the  cerebellum  and  the  medulla 
oblongata. 

The  cisterna  pontis  is  the  name  given  to  another  of  these  recesses.  It  is 
the  continuation  upwards,  on  the  floor  of  the  cranium,  of  the  anterior  part 
of  the  subarachnoid  space  of  the  spinal  meninges.  In  the  region  of  the 
medulla  oblongata  it  is  continuous  on  either  side  with  the  cerebello-medul- 
lary  cistern,  so  that  this  subdivision  of  the  brain  is  completely  surrounded 
by  a  wide  subarachnoid  space.  Within  the  cisterna  pontis  are  the  vertebral 
and  basilar  arteries. 

Anterior  to  the  pons  the  arachnoid  membrane  crosses  between  the  pro- 


Lateral  lacuna 

Arachnoideal    \ ^   ^„  ^»»*»  y»r^.^— •-—«__       / 

granulation^^P^^^i^?^^^^!^^ 


Arachnoideal  granulation 
Lateral  lacuna 


y' 


Superior  sagittal  sinus 


Blood  vessels 

Grey  cortex 

of a  gyrus 


)ura  mater 


Pia  mater 
Subarachnoid  space 

■Arachnoid 


Falx  cerebri 


Fig.  176. — Diagram  of  a  frontal  section  through  the  middle  portion  of  the 
cranial  vault  and  subjacent  brain  to  show  the  membranes  of  the  brain 
and  the  arachnoideal  granulations. 


jecting  temporal  lobes,  and  covers  in  the  deep  hollow  in  this  region  of  the 
base  of  the  brain.  This  space  is  called  the  cisterna  inierpechincitlai-is, 
and  within  it  are  placed  the  large  arteries  which  take  part  in  the  forma- 
tion of  circulus  arteriosus.  It  is  continuous  anteriorly  with  the  cisterna 
chiasniatis,  which  lies  anterior  to  the  optic  chiasma  and  lodges  the  anterior 
cerebral  arteries. 

All  the  subarachnoid  cisterns  communicate  in  the  freest  manner  with 
one  another,  and  also  with  the  narrow  intervals  on  the  surface  of  the  cere- 
brum. The  subarachnoid  space  does  not  communicate  in  any  way  with 
the  subdural  space.  In  certain  localities,  however,  it  communicates  with 
the  ventricular  system  of  the  brain.  Three  such  apertures  are  described  in 
connection  with  the  fourth  ventricle,  whilst  another  slit,  on  each  side,  is  said 
to  lead  from  the  cisterna  interpeduncularis  into  the  lower  end  of  the  corre- 
sponding inferior  horn  of  the  lateral  ventricle- 
Extending  laterally  from  the  cisterna  interpeduncularis,  on  each  side, 
is  the  cisterna  fossie  lateralis  cerebri,  which  extends  along  the  stem  of  the 
lateral  fissure  into  the  lateral  fossa,  around  the  middle  cerebral  artery. 
Anteriorly  the  cisterna  chiasmatis  is  continuous  with  a  prolongation  which 


442  THE  BRAIN 

extends  into  the  longitudinal  fissure  with  the  anterior  cerebral  arteries. 
A  dilatation  of  the  subarachnoid  space  over  the  dorsum  of  the  mid-brain 
round  the  great  cerebral  vein  (O.T,  vena  magna  Galeni)  is  called  the 
cistenia  vence  jiiag/ue  cerebri. 

Granulationes  Araclinoideales  (O.T.  Pacchionian  Bodies). 

— The  connection  of  the  arachnoideal  granulations  with  the 
arachnoid  has  been  referred  to  already  (p.  202). 

Pia  Mater  Encaphali. — The  pia  mater  forms  the  immediate 
investment  of  the  brain.  It  is  finer  and  more  delicate  than 
the  corresponding  membrane  of  the  spinal  medulla,  and  it 
follows  closely  all  the  inequalities  on  the  surface  of  the  brain. 
Thus,  in  the  case  of  the  cerebrum,  it  lines  both  sides  of  every 
sulcus  and  forms  a  fold  within  it.  On  the  cerebellum  the 
relation  is  not  so  intimate  ;  it  is  only  the  larger  fissures  of 
the  cerebellum  which  contain  folds  of  pia  mater. 

It  has  been  noted  that  the  larger  blood  vessels  of  the 
brain  run  in  the  subarachnoid  space ;  the  finer  twigs  enter  the 
pia  mater  and  ramify  in  it  before  passing  into  the  substance 
of  the  brain.  As  they  enter  they  carry  with  them  sheaths 
derived  from  the  pia  mater.  Consequently,  if  the  dissector 
raises  a  portion  of  this  membrane  from  the  surface  of  the 
cerebrum,  a  number  of  fine  processes  will  be  seen  to  be  with- 
drawn from  the  cerebral  substance.  These  are  the  blood- 
vessels, and  they  give  the  deep  surface  of  the  membrane  a 
rough  and  flocculent  appearance. 

The  pia  mater  is  not  confined  to  the  exterior  of  the  brain. 
A  fold  is  carried  into  its  interior.  This  will  be  exposed  in 
the  dissection  of  the  brain,  and  will  be  described  under  the 
name  of  the  tela  chorioidea  (O.T.  velum  interpositum)  of  the 
third  ventricle. 

Dissection. — The  blood  vessels  of  the  brain  should  now  be  followed  out 
as  far  as  it  is  possible  to  do  so  without  laceration  of  the  brain  substance. 
Begin  by  stripping  the  arachnoid  from  the  base  of  the  brain.  This  will 
bring  into  view  the  main  trunks.  As  the  vessels  of  the  brain  are  described, 
many  parts  which  have  not  yet  come  under  the  notice  of  the  dissector  must 
be  mentioned. 

Arteries  which  supply  Blood  to  the  Brain. — Four  main 
arterial  trunks  carry  blood  into  the  cranium  for  the  supply 
of  the  brain — viz.,  the  two  internal  carotid  arteries  and  the 
two  vertebral  arteries.  The  vertebral  arteries  enter  through 
the  foramen  magnum,  whilst  the  internal  carotid  arteries  gain 
admittance  through  the  lacerate  foramina  after  traversing  the 
carotid    canals.      These    vessels    have   been    divided    in    the 


MEMBRANES  AND   BLOOD  VESSELS  443 

removal  of  the  brain.  The  cut  ends  of  the  internal  carotids 
will  be  seen,  on  the  base  of  the  brain,  immediately  to  the 
lateral  sides  of  the  optic  nerves  ;  the  vertebral  arteries  lie 
on  the  sides  of  the  medulla  oblongata.  A  very  remarkable 
and  complete  anastomosis  takes  place  at  the  base  of  the 
brain  by  the  inosculation  of  branches  which  spring  from 
the  internal  carotid  and  vertebral  arterial  systems.  This  is 
termed  the  circulus  arteriosus  (Willis),  and  the  branches 
which  take  part  in  its  formation  lie  in  the  cisterna  inter- 
peduncularis  and  the  cisterna  chiasmatis. 

Two  systems  of  branches,  both  going  to  the  cerebrum  but 
differing  greatly  in  their  mode  of  distribution,  proceed  from 
the  vessels  forming  the  arterial  circle.  One  system  consists 
of  very  numerous  slender  twigs,  which,  as  a  rule,  come  off  in 
groups  in  certain  localities,  and  at  once  pierce  the  substance 
of  the  cerebrum  so  as  to  gain  its  interior.  These  are  the 
cejttral  or  basal  branches.  The  other  system  is  composed  of 
branches  which  ramify  over  the  surface  of  the  cerebrum,  and 
is  termed  the  system  of  cortical  branches.  The  central  parts 
of  the  brain,  including  the  basal  ganglia,  receive  their  blood- 
supply  from  the  basal  system,  and  the  vessels  which  con- 
stitute this  group  do  not  anastomose  with  each  other.  The 
cortical  vessels  supply  the  cerebral  cortex  and  the  finer 
branches,  which  ramify  in  the  pia  mater,  anastomose  with 
one  another ;  therefore,  the  neighbouring  vascular  districts  of 
the  cerebral  cortex  are  not  sharply  cut  off  from  each  other. 

Arteria  Vertebralis. — The  vertebral  artery  enters  the  sub- 
arachnoid space  in  the  upper  part  of  the  vertebral  canal  by 
piercing  the  dura  mater  and  the  arachnoid.  Gaining  the 
interior  of  the  cranium,  through  the  foramen  magnum,  it  is 
continued  upwards  on  the  side  of  the  medulla  oblongata. 
Soon  it  inclines  to  the  anterior  aspect  of  _  the  medulla 
oblongata,  and,  meeting  its  fellow  of  the  opposite  side  in 
the  median  plane,  it  unites  with  it,  at  the  lower  border  of 
the  pons,  to  form  the  basilar  artery. 

During  this  part  of  its  course  the  vertebral  artery  gives  off 
the  following  branches  : — 


1.  Posterior  spinal. 

2.  Posterior  inferior  cerebellar. 


3.  Anterior  spinal. 

4.  Bulbar. 


Arteria  Spinalis  Posterior. — This  is  the  first  branch  that 
is  given  off  after  the  vertebral  artery  pierces  the  dura  mater. 


444 


THE  BRAIN 


It  passes  downwards  on  the  spinal  medulla  along  the  line  of 
the  posterior  nerve-roots  (p.  193). 

Arteria  Cerebelli  Inferior  Posterior. — The  posterior  inferior 
cerebellar  artery  is  the  largest  branch  of  the  vertebral  artery. 
It  takes  origin  immediately  above  the  posterior  spinal  artery, 


Infundibulum 

Abducent  nerve 

Trigeminal  nerve, 

Trochlear  nerve 

Acustic  and 
facial  nerves 

Glosso-pharyn- 
geal  nerve 

Vagus  nerve 


Hypoglossal 
nerve 

Accessory  nerve 


Section  through 

the  medulla 

oblongata 


,^x.  Optic  nerve 

Internal  carotid 


Posterior 
^  I    communicating 
|U     artery 

Oculo-motor  nerve 
,      Posterior  cerebral 
-^-artery    _ 

\^ Superior 

cerebellar  artery 
Tentorium 

Basilar 
artery 

Vertebral 
artery- 
Superior  petrosal 
sinus 


Transverse  sinus 


Transverse  sinus 


Superior  sagittal  sinus 


Occipital  sinus 


Straight  sinus  divided 


Fig.  177. — Floor  of  the  cranium  after  the  removal  of  the  brain  and  the 
Tentorium  CerebeUi.  The  blood  vessels  forming  the  Circulus  Arteriosus 
have  been  left  in  place. 


and  pursues  a  tortuous  course  posteriorly,  on  the  side  of  the 
upper  part  of  the  medulla  oblongata,  among  the  fila  of  the 
hypoglossal  nerve,  and  then  among  the  fila  of  the  vagus. 
Finally,  turning  round  the  restiform  body,  it  gains  the  vallecula 
of  the  cerebellum,  where  it  ends  by  dividing  into  two  terminal 
branches.  Of  these,  one  turns  posteriorly,  in  the  vallecula, 
between  the  inferior  vermis  and  the  lateral  hemisphere  of 
the  cerebellum,   whilst   the   other   ramifies   on    the   posterior 


MEMBRANES  AND  BLOOD  VESSELS         445 

part  of  the  inferior  surface  of  the  corresponding  cerebellar 
hemisphere. 

Arteria  Spinalis  Anterior. — The  anterior  spinal  artery  arises 
near  the  lower  border  of  the  pons,  and  it  is  rare  to  find  the 
vessels  of  the  two  sides  of  equal  size.  They  converge  on 
the  anterior  surface  of  the  medulla  oblongata  and  unite, 
forming  the  commencement  of  the  median  vessel  which 
extends  downwards  on  the  ventral  face  of  the  spinal  medulla. 

The  bulbar  arteries  are  minute  vessels  which  enter  the 
substance  of  the  medulla  oblongata  ;  they  spring  both  from  the 
vertebral  artery  itself  and  also  from  its  branches. 

Arteria  Basilaris. — The  basilar  artery,  which  is  formed  by 
the  union  of  the  two  vertebral  arteries,  is  a  short  trunk.  It 
extends,  in  the  median  plane,  from  the  lower  to  the  upper 
border  of  the  pons.  At  the  latter  point  it  ends  by  dividing 
into  the  two  posterior  cerebral  arteries.  The  basilar  artery 
lies  in  the  middle  part  of  the  cisterna  pontis  and  occupies 
the  median  groove  on  the  ventral  or  anterior  surface  of  the 
pons.  Anteriorly  it  is  supported  by  the  basilar  portion  of 
the  occipital  bone  and  the  dorsum  sellae  of  the  sphenoid. 

The  branches  which  spring  from  the  basilar  artery  proceed 
laterally  for  the  most  part  from  either  side  of  the  vessel. 
They  are : — 

1.  Pontine. 

2.  Internal  auditory. 

3.  Anterior  inferior  cerebellar. 


4.  Superior  cerebellar. 

5.  Posterior  cerebral. 


Rami  ad  Pontem. — The  pontine  branches  are  numerous 
slender  twigs  which  run  laterally  on  the  surface  of  the  pons 
and  enter  its  substance. 

Arteria  Auditiva  Interna. — The  internal  auditory  artery 
will  be  seen  amongst  the  pontine  branches.  It  accompanies 
the  acustic  nerve  into  the  internal  acustic  meatus,  and  is 
distributed  to  the  internal  ear. 

Arteria  Cerebelli  Inferior  Anterior. — This  artery  inclines 
postero- laterally  to  reach  the  anterior  part  of  the  inferior 
surface  of  the  cerebellum. 

Arteria  Cerebelli  Superior. — The  superior  cerebellar  artery 
is  a  large  vessel  which  springs  from  the  basilar  close  to  its 
termination.  It  winds  laterally  and  posteriorly,  along  the 
upper  border  of  the  pons,  to  reach  the  upper  surface  of  the 
cerebellum,  upon  which  it  spreads  out  in  a  number  of  large 
branches. 


446 


THE  BRAIN 


Arteria  Cerebri  Posterior. — Immediately  beyond  the  origin 
of  the  two  superior  cerebellar  arteries  the  basilar  trunk 
bifurcates  into  the  two  posterior  cerebral  arteries.  These 
diverge  from  each  other,  and,  curving  laterally  and  posteriorly, 
encircle  the  mesencephalon.  Then  they  run  posteriorly  towards 
the  under  surface  of  the  splenium  of  the  corpus  callosum. 
In  this  course  each  posterior  cerebral  artery  lies  deeply  in 
the  interval  between  the  corresponding  pedunculus  cerebri 
and  the  hippocampal  gyrus,  and,  finally,  passing  on  to  the 
tentorial   surface   of   the    cerebral  hemisphere    it   disappears 


Posterior  medial  frontal 


Intermediate  medial  frontal 

Anterior  medial  frontal 


Parieto- 
occipital— ^  T-  ->-, — ^-^_«.^  „^^ 
branch    iJ     fi    ^\^' C  Ji 


Anterior 
medial 
frontal 
branches 

Medial  orbital 
branches 
Anterior  cerebral  artery 


Calcarine  branch  \/  Posterior  cerebral  artery 

Temporal  branches 

Fig.  178. — Medial  and  Tentorial  Surfaces  of  the  left  Cerebral  Hemisphere. 
The  district  supplied  by  the  anterior  cerebral  artery  is  tinted  purple  ;  by 
the  middle  cerebral  artery,  blue  ;  and  by  the  posterior  cerebral  artery, 
red.      (Semi-diagrammatic. ) 

from  view,  by  sinking  into  the  anterior  extremity  of  the  cal- 
carine fissure.  In  this  fissure  the  artery  ends  by  dividing  into 
two  terminal  branches,  viz.,  the  calcarine  and  the  parieto- 
occipital (Figs.  178  and  180). 

The  oculo-motor  nerve  passes  anteriorly  in  the  interval 
between  the  posterior  cerebral  and  the  superior  cerebellar 
arteries,  close  to  the  place  where  they  arise  from  the  basilar ; 
and  the  small  trochlear  nerve  winds  round  the  pedunculus 
cerebri  below  the  posterior  cerebral  artery. 


The  following  branches  spring  from  the  posterior  cerebral  artery 
r  Postero-median. 
-|  Postero-lateral. 
[  Posterior  chorioidal. 


Central  or  basal 


[  Temporal. 
Cortical    -;  Calcarine. 

\  Parieto-occipital. 


MEMBRANES  AND  BLOOD  VESSELS  447 

The  postero-i/iedian  central  arteries  arise  close  to  the  origin  of  the  parent 
trunk.  They  proceed  upwards,  in  the  interval  between  the  pedunculi  cerebri, 
and,  piercing  the  substantia  perforata  posterior  (O.T.  posterior  perforated 
space),  they  supply  the  thalami  and  the  medial  parts  of  the  pedunculi 
cerebri. 

The  postero -lateral  central  aiieries  are  a  group  of  small  slender  twigs 
which  arise  on  the  lateral  surface  of  the  pedunculus  cerebri,  and  go  to  the 
corpora  quadrigemina  and  the  thalamus. 

The  posterior  chorioidal  artery,  somewhat  larger,  goes  to  the  tela 
chorioidea  of  the  third  ventricle  and  the  chorioid  plexus  of  the  lateral 
ventricle  (Figs.  178  and  179). 

The  teiiip07'al  branches,  two  or  three  in  number,  turn  laterally,  over  the 
hippocampal  gyrus,  and  ramify  on  the  under  surface  of  the  temporal  lobe 
of  the  cerebrum  (Figs.  178  and  180). 

The  calcarine  branch  follows  the  calcarine  fissure  to  the  occipital  pole 
of  the  cerebral  hemisphere,  round  which  it  turns  to  reach  the  lateral  surface 
of  the  occipital  lobe.  It  is  the  chief  artery  of  supply  to  the  cuneus  and  the 
lingual  gyrus,  and  is  therefore  specially  concerned  in  the  nutrition  of  the 
visual  centres  of  the  cerebral  cortex  (Fig.  178). 

The  parieto-occipital  a7'tery  is  the  smaller  of  the  two  terminal  branches 
of  the  posterior  cerebral.  It  runs  upwards  in  the  parieto-occipital  fissure, 
and  reaching  the  upper  margin  of  the  cerebrum  it  turns  round  it  to 
reach  the  lateral  surface  of  the  occipital  lobe.  It  supplies  branches  to  the 
cuneus  and  praecuneus  (Figs.  178,  180). 

Arteria  Carotis  Interna. — The  cut  extremity  of  this  great 
vessel  lies  on  the  lateral  side  of  the  optic  chiasma,  in  the 
angle  between  the  optic  nerve  and  the  optic  tract.  At  the 
substantia  perforata  anterior,  close  to  the  commencement  of 
the  lateral  fissure,  it  ends  by  dividing  into  the  anterior  and 
middle  cerebral  arteries  (Fig.  179).  T\\q  middle  cerebral  artery 
is  the  larger  of  the  two  terminal  branches,  and,  as  it  enters  the 
lateral  (O.T.  Sylvian)  fissure,  it  appears  to  be  the  continuation 
of  the  parent  trunk.  The  anterior  cerebral  artery^  on  the 
other  hand,  proceeds  medially  from  the  internal  carotid  at 
almost  a  right  angle.  This  explains  how  it  is  that  emboli 
pass  more  frequently  into  the  middle  cerebral  than  into  the 
anterior  cerebral  artery.  From  the  internal  carotid  artery, 
after  it  has  emerged  from  the  cavernous  sinus  (p.  331),  the 
following  branches  arise  : — 


^to 


1.  Ophthalmic  (already  studied, 

p.  341)- 

2.  Posterior  communicating. 


3.  Chorioidal. 

4.  Middle  cerebral. 

5.  Anterior  cerebral. 


Arteria  Co7nmimicans  Posterior. — This,  as  a  rule,  is  a 
slender  branch  which  passes  posteriorly  to  join  the  posterior 
cerebral  between  its  postero-median  and  postero-lateral  groups 
of  basal  twigs  (Fig.  181). 

Arteria    Chorioidea. —  The    chorioidal    artery    enters    the 


448 


THE  BRAIN 


inferior   cornu   of  the  lateral  ventricle,   and   passes    into   the 
chorioid  plexus  in  that  cavity  (Fig.  179). 

Arteria  Cerebri  Anterior. — The  anterior  cerebral  runs  first 
horizontally,  above  the  optic  chiasma,  towards  the  median  plane 
(Figs.  178,  179).  Then,  bending  sharply  upon  itself,  it  turns 
upwards  in  the  anterior  part  of  the  longitudinal  fissure,  anterior 


Medial  orbital  branches 


Olfactory  sulcus 


Lateral  orbital  branches 


Anterior  cerebral  artery 


Anterior  communicating 
Internal  carotid  artery  _i^|^ 
Middle  cerebral  artery  --^^^^ 

Posterior  communicating— 


Superior  cerebellar  artery 

Basilar  artery' 

Posterior  chorioidal  artery 

Posterior  cerebral  artery 
Calcarine  fissure 


Chorioidal  branch  of 
internal  carotid 


Temporal 
branches 


Inferior  temporal 
sulcus 


Collateral  fissure 


Fig.  179. — Inferior  Surface  of  the  Cerebral  Hemisphere.  The  districts  sup- 
plied by  the  three  cerebral  arteries  are  tinted  differently  :  posterior  cerebral 
artery,  red;  middle  cerebral  artery,  blue\  anterior  cerebral  2lX\.q.xy ,  purple. 


to  the  lamina  terminalis,  and  along  the  rostrum  to  the  genu 
of  the  corpus  callosum,  round  which  it  bends ;  then  it  passes 
posteriorly  along  the  medial  face  of  the  hemisphere,  on  the 
upper  surface  of  the  corpus  callosum,  to  the  parieto-occipital 
fissure  (Fig.  178).  As  it  lies  anterior  to  the  lamina  terminalis 
it  is  connected  with  the  opposite  anterior  cerebral  artery  by 
the  anterior  communicating  artery.^  and  as  it  passes  along  the 
longitudinal  fissure,  between  the  hemispheres,  it  lies  close  to 
its  fellow  of  the  opposite  side. 


MEMBRANES  AND  BLOOD  VESSELS 


449 


Numerous  branches  proceed  from  the  anterior  cerebral  artery  : — 

Basal  or  central  {  Antero-median, 

Medial  orbital. 
Anterior  medial  frontal. 


Cortical 


il 


Intermediate  medial  frontal. 
Posterior  medial  frontal. 


The  ante7'o-niedia)i  arlei'ies  pierce  the  base  of  the  brain  anterior  to  the 
optic  chiasma.  They  supply  the  rostrum  of  the  corpus  callosum,  the 
lamina  terminalis,  and  the  septum  pellucidum. 

The  medial  orbital  branches  are  two  or  three  in  number.  They  turn 
round  the  margin  of  the  longitudinal  fissure  to  reach  the  medial  part  of  the 


Ascending  parietal  arterj' 
Ascending  frontal  artery' 


Precentral  '-ulrns 
Inferior  frontal 
sulcus 


'^'¥^. 


Central  sulcus 

Parieto-temporal  artery 


Superior 
frontal 
sulcus 


Parieto- 
occipital 

fissure 

(Lateral 

part) 


Inferior  lateral  frontal 
artery 
Posterior  branch  of  lateral  fissure 

Temporal  branches 

Fig.  I  8o.  ^Lateral  Surface  of  the  Cerebral  Hemisphere.  The  districts  supplied 
b}'  the  three  cerebral  arteries  are  tinted  differently  :  anterior  cerebral, 
piirple;  middle  cerebral,  blue;  posterior  cerebral,  red.  (Semi-diagram- 
matic. ) 


orbital  surface  of  the  frontal  lobe.  They  supply  the  g>'rus  rectus,  the  olfactory 
tract  and  bulb,  and  the  medial  orbital  gyrus  (Figs.  178  and  179). 

The  anterior  medial  fro7ital  artery  ramifies  upon  the  anterior  part  of  the 
medial  surface  of  the  frontal  lobe,  and  its  terminal  twigs  turn  round  the 
upper  margin  of  the  cerebral  hemisphere,  and  supply  the  upper  part  of  the 
lateral  surface  of  the  frontal  lobe  (Fig.  178). 

The  intermediate  medial  fro7ital  ariery  ramifies  on  the  medial  surface 
of  the  frontal  lobe  posterior  to  the  preceding  branch.  Its  terminal  part 
passes  over  the  paracentral -lobule,  and  reaches  the  adjacent  portion  of  the 
lateral  surface  of  the  cerebral  hemisphere  (Fig.  178). 

The  poste7'ior  medial  frojital  arteiy  ramifies  on  the  medial  surface  of 
the  pr^ecuneus,  and  its  terminal  twigs  turn  round  the  upper  margin  of 
the  cerebral  hemisphere  to  gain  the  lateral  surface. 

Arteria  Cerebri  Media. — At  first  the  middle  cerebral  artery 
passes  laterally  and  then  upwards  in  the  lateral  fissure.      It 

VOL.  II — 29 


450  THE  BRAIN 

soon  breaks  up  into  a  number  of  large  terminal  branches, 
which  spread  out  on  the  surface  of  the  insula.  Before  the 
posterior  ramus  of  the  lateral  fissure  is  opened  up,  to  expose 
the  insula,  these  branches  may  be  seen  emerging  from  between 
its  two  lips  (Fig.  1 80).  Then  they  diverge  and  supply  a 
wide  area  of  cortex  on  the  lateral  surface  of  the  hemisphere. 

The  branches  which  spring  from  the  middle  cerebral  artery  may  be 
classified  as  follows  : — 

Central  or  basal       1    a    ^        it      i 
11  y  Antero-Iateral. 

branches.  j 


Cortical  branches. 


/-  (  Lateral  orbital. 

Frontal        -    Inferior  lateral  frontal. 
(^  Ascending  frontal. 

Parietal         {  Ascending  parietal. 


Parieto-temporaL 
'^  Temporal. 

The  arteries  of  the  ant ero -lateral  basal  grotip  are  very  numerous.  They 
pierce  the  substantia  perforata  anterior  and  supply  the  lentiform  nucleus, 
the  internal  and  the  external  capsule,  the  caudate  nucleus,  and  a  portion  of 
the  thalamus. 

The  frontal  and  parietal  branches  turn  round  the  upper  lip  of  the 
posterior  ramus  of  the  lateral  fissure  and  ascend  on  the  lateral  surface  of  the 
hemisphere.  The  frojital  branches  are  :  ( I )  lateral  orbital  to  the  lateral 
part  of  the  orbital  surface  of  the  frontal  lobe  ;  (2)  inferior  lateral  frontal 
to  the  inferior  and  middle  frontal  gyri ;  (3)  ascending  frontal,  which  runs 
upwards  in  relation  to  the  anterior  central  gyrus. 

The  ascending  parietal  branch  extends  in  an  upward  and  posterior 
direction  in  relation  to  the  postcentral  gyrus,  and  its  terminal  twigs  supply 
the  greater  part  of  the  cortex  of  the  superior  parietal  lobule. 

The  parieto-temporal  bi'anch  is  a  very  large  artery  which  issues  from 
the  posterior  part  of  the  posterior  branch  of  the  lateral  fissure  ;  it  sends 
branches  upwards  to  the  inferior  parietal  lobule,  and  others  which  incline 
downwards  over  the  posterior  part  of  the  temporal  lobe.  Its  twigs,  as 
a  rule,  do  not  encroach  upon  the  lateral  surface  of  the  occipital  lobe. 

The  temporal  branches,  two  or  three  in  number,  issue  from  the  posterior 
ramus  of  the  lateral  fissure,  and,  turning  downwards  and  posteriorly,  over 
its  lower  lip  {i.e.  the  superior  temporal  gyrus),  they  ramify  upon  the 
lateral  surface  of  the  temporal  lobe. 

Circulus  Arteriosus  (O.T.  Circle  of  Willis). — This  re- 
markable anastomosis  is  placed  beneath  the  base  of  the  brain 
in  the  deep  hollow  anterior  to  the  pons.  It  takes  the  form 
of  a  heptagonal  or  hexagonal  figure,  and  the  vessels  which 
compose  it  lie  in  the  cisterna  interpeduncularis  and  the  cisterna 
chiasmatis.  Anteriorly  it  is  closed  by  the  anterior  communi- 
cating artery  which  links  together  the  two  anterior  cerebral 
arteries.  On  either  side  is  the  posterior  communicating 
artery  connecting  the  internal  carotid  (from  which  the  anterior 


MEMBRANES  AND  BLOOD  VESSELS 


451 


cerebral  springs)  with  the  posterior  cerebral.  The  arterial 
ring  is  completed  posteriorly  by  the  bifurcation  of  the  basilar 
artery  into  the  two  posterior  cerebral  vessels  (Fig.  181).  As 
a  rule  the  circulus  arteriosus  is  not  symmetrical.  One  posterior 
communicating  artery  is  almost  invariably  larger  than  its  fellow 
of  the  opposite  side. 

Dissection. — The    brain   being   placed    with   its  base    uppermost,    the 
dissector  should  proceed  to  remove  the  blood  vessels  and  membranes  from 


Anterior  cerebral  artery 


/.Anterior  communicating 
Internal- carotid 


Middle  cerebral 


Antero-lateral  basal  arteries 
Posterior  communicating 

Postero-median  basal  arteries 
Posterior  cerebral  artery 


Superior  cerebellar  artery 


Fig.    181. — Diagram  of  the  Circulus  Arteriosus. 

its  surface.  This  must  be  done  with  the  forceps  and  a  pair  of  scissors. 
It  is  a  dissection  which  requires  very  delicate  manipulation,  because  the 
cerebral  nerves,  at  their  points  of  attachment  to  the  brain,  are  so  intimately 
connected  with  the  pia  mater  that  any  undue  traction  applied  to  the 
membranes  will  tear  the  nerves  away.  Indeed,  in  the  case  of  the 
medulla  oblongata,  the  dissector  is  advised  to  leave  the  pia  mater  in 
position  until  the  nerve  roots  have  been  studied.  The  relation  of  the  pia 
mater  to  the  fourth  ventricle  also  renders  this  desirable. 

In  removing  the  arachnoid  and  pia  mater  from  the  lateral  surface  of 
the  cerebrum,  it  is  well  to  raise  it  first  from  the  margins  of  the  hemisphere, 
and  then  to  work  towards  the  lateral  fissure  (Sylvian).  By  this  method,  the 
membranes  and  vessels  within  this  great  fissure  and  in  relation  to  the 
insula  can  be  withdrawn  without  damage  to  the  brain  substance.  Of 
course,  at  the  present  stage,  the  membranes  cannot  be  removed  from 
every  part  of  the  brain  ;  but  as  the  dissection  proceeds,  opportunities  for 
completing  the  process  will  arise. 
11—29  « 


452  THE,  BRAIN 


BASE  OF  BRAIN. 

Fossa  Interpeduncularis. — When  the  membranes  are  re- 
moved from  the  base  of  the  brain,  \he  pedunculi  cerebri  (O.T. 
crura),  two  large  rope-hke  strands,  will  be  seen  issuing  from  the 
upper  aspect  of  the  pons.  Placed  close  together  as  they 
emerge  from  the  pons,  they  diverge  as  they  proceed  upwards 
and  anteriorly,  and,  finally,  each  peduncle  disappears  into  the 
corresponding  half  of  the  cerebrum.  Turning  round  the 
lateral  aspect  of  each  peduncle,  where  it  passes  into  the 
cerebrum,  will  be  seen  a  flattened  band,  called  the  oJ)tic  tract. 
These  bands  converge  as  they  pass  anteriorly,  and  are  finally 
joined  together  by  a  short  transverse  commissural  portion, 
termed  the  optic  chiasma.  This  chiasma  is  placed  below  the 
posterior  end  of  that  portion  of  the  longitudinal  fissure  which 
intervenes  between  the  inferior  surfaces  of  the  frontal  lobes 
of  the  cerebrum.  The  optic  nerves  run  antero-laterally  from 
the  chiasma. 

The  cerebral  peduncles,  the  optic  tracts,  and  the  optic 
chiasma  enclose  a  deep  rhomboidal  or  lozenge-shaped  interval 
on  the  base  of  the  brain,  which  is  termed  the  interpeduncular 
fossa.  Within  the  limits  of  this  area  the  following  parts  may 
be  seen.  The  substantia  perforata  posterior  bounded  an- 
teriorly by  the  corpora  majjiillaria ;  anterior  to  the  corpora 
mamillaria  is  the  tuber  cinereum,  and  attached  to  it  is  the 
infundibulu7n  of  the  hypophysis.  These  structures  take  part  in 
the  formation  of  the  floor  of  the  third  ventricle  of  the  brain. 

The  oculo-motor  nerves  issue  from  the  brain  within  the 
interpeduncular  fossa.  Each  nerve  emerges  from  the  medial 
side  of  the  corresponding  pedunculus  cerebri. 

Substantia  Perforata  Posterior  (O.T.  Posterior  perforated 
space). — At  its  posterior  angle,  immediately  anterior  to  the 
pons,  the  interpeduncular  fossa  is  very  deep,  and  is  roofed 
by  a  layer  of  grey  matter  in  which  are  numerous  small 
apertures.  This  is  the  substantia  perforata  posterior.  From 
the  apertures  which  are  dotted  over  its  surface  the  postero- 
median basal  branches  of  the  posterior  cerebral  artery  have 
been  withdrawn. 

Corpora  Mamillaria. — These  are  two  small,  white,  pea- 
shaped  eminences  placed,  side  by  side,  anterior  to  the  sub- 
stantia perforata  posterior.     At  a  later  stage  of  the  dissection 


BASE  OF  BRAIN 


453 


their   connections   with   the   columns  of   the   fornix    will   be 
displayed. 

Tuber  Cinereum. — This  is   a   slightly  raised  field  of  grey 
matter    which    occupies    the    interval    between    the    corpora 


Optic  chiasma 


Infundibu 


Corpora 
mami  liana 


Substantia 
perforata 

pobtenn 


Olfactory  bulb 


Olfactory  tract 


Optic  nerve 

Substantia  perfor- 
1    ata  anterior 


Optic  tract 


]Motor  root  of 
facial  nerve 

Acustic  nerve 

Sensory  root  of 
facial  nerve 


Glosso-pharyngeal 
nerve 


jlossal 
nerve 


Pyramid 
Spinal  medulla  (cut) 


Vagus  nerv'e 
ssorj^  nerve 
Hypoglossal  nerve 


Fig.  182. — The  Base  of  the  Brain  with  the  Cerebral  Nerves  attached. 


mamillaria  posteriorly,  the  optic  chiasma  anteriorly,  and  the 
optic  tracts  laterally.  Springing  from  the  anterior  part  of  the 
tuber  cinereum,  immediately  posterior  to  the  optic  chiasma, 
is   the    infundibulum    or  stalk   of  the    hypophysis.       In    the 


11—29  6 


454  THE  BRAIN 

removal  of  the  brain  its  connection  with  that  body  was 
severed. 

Substantise  Perforatse  Anteriores.  —  These  are  small 
triangular  districts  of  grey  matter,  one  on  each  side.  Each 
is  bounded  posteriorly  by  the  uncinate  extremity  of  the  hippo- 
campal  gyrus ;  anteriorly  by  the  diverging  striae  of  the 
olfactory  tract ;  and  medially  by  the  optic  tract.  Laterally 
it  passes  into  the  roof  of  the  lateral  fissure,  and  is  perforated 
by  the  antero-lateral  basal  arteries.  The  grey  matter  in  this 
area  is  continuous  above  with  the  grey  matter  of  the  lentiform 
nucleus  (O.T.  lenticular). 

Lamina  Terminalis. — If  the  anterior  border  of  the  optic 
chiasma  is  displaced  posteriorly  a  thin  lamina  will  be  noticed. 
It  passes  upwards  from  the  chiasma  into  the  longitudinal 
fissure,  to  become  connected  with  the  rostrum  of  the  corpus 
callosum.  This  is  the  la77iina  terminalis.  It  closes  the  third 
ventricle  anteriorly,  and  is  continuous  on  either  side  with  the 
grey  matter  of  the  substantia  perforata  anterior. 

Superficial  Origins  of  the  Cerebral  Nerves.  —  Twelve 
cerebral  nerves  are  enumerated  arising  from  the  brain  on  either 
side  of  the  median  plane.  They  are  the  olfactory  or  first ; 
the  optic  or  second;  the  oculo-motor  or  third;  the  troch- 
lear or  fourth ;  the  trigeminal  or  fifth ;  the  abducent  or 
sixth ;  the  facial  or  seventh ;  the  acustic  or  eighth ;  the 
glosso-pharyngeal  or  ninth;  the  vagus  or  tenth  ;  the  accessory 
or  eleventh ;  and  the  hypoglossal  or  twelfth. 

Each  of  these  nerves  is  said  to  have  a  "  superficial "  and  a 
"  deep  "  origin.  By  the  term  "  superficial  origin  "  is  meant 
the  region  where  its  fibres  enter  or  leave  the  brain  surface ; 
the  term  "  deep  origin  "  indicates  the  connections  which  are 
established  by  the  fibres  of  the  different  nerves  with  nuclei  or 
clusters  of  nerve-cells  within  the  substance  of  the  brain.  These 
nuclei  are  of  two  kinds:  (i)  those  in  connection  with  which 
the  afferent  or  entering  nerve  fibres  end;  and  (2)  those  from 
which  the  efferent  or  emerging  nerve  fibres  arise.  It  is  the 
superficial  attachments  only  which  come  under  notice  of  the 
dissector  at  the  present  time. 

No  fewer  than  eight  of  the  cerebral  nerves  have  a  superficial 
attachment  to  the  ventral  part  of  the  hind  brain  which  is 
formed  by  the  medulla  oblongata  and  the  pons. 

Hypoglossal  Nerve. — Upon  the  lateral  aspect  of  the 
medulla  oblongata,   in  its  upper  half,   is  a  very  conspicuous 


BASE  OF  BRAIN 


455 


oval  prominence  called  the  olive.  A  distinct  sulcus  or  groove, 
which  passes  downwards  anterior  to  this  body,  separates  it 
from  an  elongated  strand,  termed  the  pyramid  of  the  medulla 
oblongata.  From  the  bottom  of  this  sulcus  and  its  prolonga- 
tion downwards  issue  a  series  of  nerve  fila  which  belong  to  two 
different  nerves.  Those  which  issue  from  the  lower  part  of 
the  groove,  below  the  level  of  the  olive,  belong  to  the  a?iterwr 
root  of  the  first  cervical  Jierve ;  those  which  emerge  from  the 


Optic  chiasma 

Optic  tract 

Corpus  geniculatum 
laterale 

Corpus  geniculatum 
mediale 

Substantia  perforata 
posterior 


Brachium  pontis 


Restiform  body 
Olive 

Pyramid 

External  arcuate 

fibres' 

Decussation  of 
pyramids 


t\_y^ 


-Optic  nerve 
-Infundibulum 
Tuber  cinereum 

Corpus  mamillare 

Oculo-motor  nerve 

(III.) 

irochlear  nerve  (iv.) 

winding  round  pedun- 

culus  cerebri 


Trigeminal  nerve  (\.) 
Abducent  nerve  (vi.) 
Facial  nerve  (vii.) 
Acustic  nerve  (viii.) 

Vago-glosso-pharj^n- 
geal  nerve  (ix.  and  x.) 

Fila  of  h^-poglossal 
nerve  (xn.)  cut  short 

Accessory  nerve  (xi.) 
First  cervical  nerve 


Fig.  183. — Anterior  aspect  of  the  Medulla  oblongata,  Pons,  and 
Mesencephalon  of  a  full-time  Foetus. 


upper  part  of  the  groove,  in  the  interval  between  the  olive 
and  the  pyramid,  form  the  hypoglossal  nerve. 

Glosso-pharyngeal,  Vagus,  and  Accessory  Nerves. — Posterior 
to  the  olive,  in  the  postero -lateral  sulcus  of  the  medulla 
oblongata,  is  another  continuous  row  of  nerve  fila.  These 
extend  downwards,  beyond  the  level  of  the  olive,  and  are 
attached  to  the  whole  length  of  the  medulla  oblongata  in 
linear  order.  They  belong  to  three  nerves,  but  it  is  im- 
possible at  present  (seeing  that  the  nerve -trunks  which  they 


456 


THE  BRAIN 


build  up  are  divided)  to  determine  precisely  the  number  of 
fila  which  belong  to  each.  From  below  upwards  the  nerves 
which  they  form  are  the  accessory^  the  vagus,  and  the  glosso- 
pharyngeal. The  fila  of  the  vagus  and  the  glosso-pharyngeal 
are  much  more  closely  crowded  together  than  those  of  the 
accessory. 

The  roots  of  the  accessory,  which  spring  from  the  medulla 
oblongata,  constitute  only  one  part  of  the  nerve.     The  spinal 


Oculo-motor  nerve 


Trochlear  nerve 

Sensory  root  of  the  trigeminal  nerve 
Motor  root  of  the  trigeminal 

Abducent  nerve 

Motor  root  of  facial 
nerve 

Cut  edge  of  the 
tentorium 


'—Sensory  root  of 

facial  nerve 
Acustic  nerve 

Right  transverse 
sinus 
Glosso-pharyngeal 
nei\e 
Vagus  nerve 

Accessory  nerve 


W    Vertebral  artery 
Hypoglossal  nerve 
First  spinal  nerve 
Accessory  nerve 


Fig.  184. — Section  through  the  Head  a  little  to  the  right  of  the  Median 
Plane.  It  shows  the  posterior  cranial  fossa  and  the  upper  part  of  the 
vertebral  canal  after  the  removal  of  brain  and  the  spinal  medulla. 


part  springs  from  the  spinal  medulla,  as  low  down  as  the  sixth 
cervical  nerve,  by  a  series  of  roots  which  issue  from  the  lateral 
funiculus,  posterior  to  the  attachment  of  the  ligamentum 
denticulatum. 

Acustic  and  Facial  Nerves. — These  issue  close  together 
at  the  lower  border  of  the  pons,  and  immediately  above  the 
restiform  body.  The  acustic  7ierve  is  the  larger  of  the  two, 
and  it  lies  on  the  lateral  side  of  the  facial.  Its  two  roots, 
termed  the  cochlear  and  the  vestibular,  embrace  the  restiform 
body. 


BASE  OF  BRAIN 


457 


The  facial  7ierve  issues  from  the  pons  close  to  its  lower 
border,  and  just  to  the  medial  side  of  the  acustic  nerve, 
by  two  roots,  a  large  motor  root,  and  a  small  sensory  root 
(O.T.  pars  intermedia).  The  two  roots  unite  in  the  internal 
acustic  meatus. 

Abducent  Nerve. — This  is  a  small  nerve  which  emerges 
from  the  groove  between  the  lower  border  of  the  pons  and  the 
lateral  part  of  the  pyramid. 

Trigeminal  Nerve. — This  is  the  largest  of  all  the  cerebral 
nerves.     It  appears  at  the  side  of  the  pons,  nearer  its  upper 


A.  Cerebral  hemisphere. 

B.  Cerebellum. 

D.  Medulla  oblongata. 

C.  Pons. 

a.  Mesencephalon. 

c.  Brachium  pontis. 

d.  Restiform  body. 

e.  Lateral  fissure. 


Fig.  185. — Diagrammatic  view  of  the  manner  in  which  the  several  parts  of 
the  Brain  are  connected  with  one  another.      (From  Schwalbe. ) 

than  its  lower  border  and  in  a  Hne  wdth  the  facial  and  acustic 
nerves.  It  consists  of  two  roots — a  large  sensory  root,  portio 
major,  composed  of  a  great  number  of  fila  loosely  held  together, 
and  a  small,  more  compact  motor  root,  portio  minor,  which 
emerges  antero-medial  to  the  point  at  which  the  sensory  root 
enters  the  pons. 

Trochlear  Nerve. — The  superficial  origin  of  the  trochlear 
or  fourth  nerve  cannot  be  seen  at  present.  It  emerges  from 
the  anterior  niedullary  velum,  on  the  dorsal  aspect  of  the 
brain-stem.  It  is  a  delicate  little  nerve  which  has  a  long 
intracranial  course.  It  winds  round  the  lateral  side  of  the 
pedunculus  cerebri,  between  the  cerebrum  and  cerebellum. 


458  THE  BRAIN 

Oculo  -  motor  Nerve.  —  This  may  be  seen  within  the 
interpeduncular  fossa.  It  issues  by  several  fila  from  the 
sulcus  oculomotorius  on  the  medial  face  of  the  cerebral 
peduncle. 

Optic  Nerve. — This  is  a  large  round  nerve  which  passes 
antero-laterally  from  the  optic  chiasm  a. 

Olfactory  Nerves. — These  arise  from  the  olfactory  bulb 
and  enter  the  nasal  cavity  through  the  foramina  in  the 
cribriform  plate  of  the  ethmoid  bone. 

General  Connections  of  the  Several  Parts  of  the  Brain. — 
Before  proceeding  to  the  more  particular  study  of  the  different 
parts  of  the  brain  the  student  should  acquire  a  general 
conception  of  the  manner  in  which  these  are  connected  with 
each  other.  In  the  posterior  cranial  fossa,  below  the  ten- 
torium, are  placed  the  medulla  oblongata,  the  pons,  and 
the  cerebellum,  which  constitute  collectively  the  Rhoi7iben- 
cephalon  or  hind-brain.  They  surround  a  cavity  which  is 
called  the  fourth  ventricle  of  the  brain,  and  all  stand  in 
intimate  connection  with  one  another.  The  upper  end  of 
the  medulla  oblongata  terminates  chiefly  in  the  pons,  but  two 
large  strands  on  its  posterior  or  dorsal  aspect,  termed  the 
restiform  bodies,  pass  posteriorly  into  the  cerebellum  (Fig. 
185,  d).  The  transverse  fibres  of  the  pons  are  gathered 
together  on  either  side  in  the  form  of  a  large  rope-like  strand, 
the  brachiutn  pontis.  This  disappears  into  the  corresponding 
hemisphere  of  the  cerebellum  (Fig.  185,  c). 

The  great  mass  of  the  brain  is  termed  the  cerebrum. 
This  occupies  the  anterior  and  middle  cranial  fossse,  and 
extends  posteriorly  into  the  occipital  region  above  the 
tentorium  cerebelli.  The  greater  part  of  the  cerebrum  is 
formed  by  the  cerebral  hemispheres,  which  are  separated 
from  each  other,  in  the  median  plane,  by  the  longitudinal 
fissure.  At  the  bottom  of  this  fissure  may  be  seen  the  corpus 
cailosu/n,  a  broad  commissural  band  which  connects  the  two 
cerebral  hemispheres  with  each  other.  Each  hemisphere  is 
hollow — the  cavity  in  its  interior  being  termed  the  lateral 
ventricle  of  the  brain.  Between  and  below  the  cerebral 
hemispheres,  and  almost  completely  concealed  by  them,  is 
the  thalamencephalon.  The  principal  parts  forming  this  portion 
of  the  brain  are  the  two  thalami,  between  which  is  the  third 
ventricle  of  the  brain — a  deep,  narrow  cavity  occupying  the 
median  plane.     The  third  ventricle  communicates  with  the 


THE  CEREBRUM  459 

lateral  ventricles  through  the  forame?i  interventriculare  (O.T. 
foramen  of  Monro). 

The  cerebrum  is  connected  with  the  parts  in  the  posterior 
cranial  cavity  (pons,  cerebellum,  and  medulla  oblongata)  by 
a  narrow  stalk  called  the  7fiid-bratn,  or  mesencephalon.  The 
mid-brain  is  built  up  of  a  ventral  portion,  the  pedunculi 
cerebri,  passing  between  the  pons  and  the  cerebrum  (Fig. 
185,  a).,  and  a  dorsal  portion,  the  lamina  quadrigemina. 
It  is  tunnelled  by  a  narrow  passage — the  aqiiceductus  cerebri 
(O.T.  aqiceduct  of  Sylvius) — which  connects  the  fourth  and 
the  third  ventricles. 


THE  CEREBRUM. 

Cerebral  Hemispheres. — Each  cerebral  hemisphere  presents 
a  lateral,  a  medial,  and  an  inferior  surface,  which  are  separated 
from  one  another  by  more  or  less  distinctly  marked  borders. 
The  lateral  S2irface  is  convex,  and  is  adapted  to  the  concavity 
of  the  cranial  vault.  The  medial  surface  is  fiat  and  perpen- 
dicular, and  is  more  or  less  completely  separated  from  the 
corresponding  surface  of  the  opposite  hemisphere  by  the  falx 
cerebri,  which  occupies  the  longitudinal  fissure.  The  inferior 
surface  is  irregular,  and  is  adapted  to  the  anterior  and  middle 
cranial  fossse,  and  also  to  the  upper  surface  of  the  tentorium 
cerebelli.  Traversing  this  surface,  in  a  transverse  direction, 
nearer  the  anterior  than  the  posterior  end  of  the  hemisphere, 
is  the  stem  of  the  lateral  fissure  (O.T.  Sylvian)  (Fig.  182). 
This  deep  cleft  divides  the  inferior  surface  into  an  anterior 
or  orbital  area,  which  rests  upon  the  orbital  plate  of  the  frontal 
bone  and  is,  consequently,  concave  from  side  to  side,  and  a 
more  extensive  posterior  or  tentorial  area,  which  lies  on  the 
floor  of  the  lateral  part  of  the  middle  cranial  fossa  and  the 
upper  surface  of  the  tentorium  cerebelli.  The  tentorial 
portion  of  the  inferior  surface  is  arched  antero- posteriorly, 
and  looks  medially  as  well  as  downwards. 

The  borders  which  separate  the  surfaces  from  each 
other  are  the  supero-medial,  the  superciliary,  the  infero- 
lateral,  the  medial  occipital,  and  the  medial  orbital.  The 
supero-medial  border,  convex  antero-posteriorly,  intervenes 
between  the  medial  and  lateral  surfaces.  The  superciliary 
border   is    highly    arched,   it    separates    the    orbital    surface 


46o  THE  BRAIN 

from  the  lateral  surface.  The  infero-lateral  border  marks  off 
the  tentorial  part  of  the  inferior  surface  from  the  lateral 
surface.  The  medial  occipital  border  is  not  very  distinct, 
except  in  cases  where  the  brain  has  been  hardened  in  situ. 
It  extends  from  the  posterior  extremity  of  the  hemisphere  to 
the  posterior  end  of  the  corpus  callosum,  and  intervenes 
between  the  medial  surface  and  the  tentorial  part  of  the  inferior 
surface.  The  medial  orbital  margin  extends  from  the  frontal 
pole  to  the  lamina  terminalis  and  separates  the  orbital  from 
the  medial  surface. 

The  most  projecting  part  of  the  anterior  end  of  the 
cerebral  hemisphere  is  called  the  frontal  pole^  whilst  the 
most  projecting  part  of  the  posterior  end  is  termed  the 
occipital  pole.  On  the  under  surface  of  the  hemisphere,  the 
prominent  rounded  portion  of  cerebral  substance  which  ex- 
tends anteriorly  below  the  lateral  fissure  receives  the  name  of 
the  temporal  pole.  In  a  well-hardened  brain  a  broad  groove  is 
usually  present  on  the  medial  aspect  of  the  occipital  pole  of 
the  right  hemisphere.  This  corresponds  to  the  termination 
superior  sagittal  venous  sinus. 

Longitudinal  Fissure. — This  great  median  cleft  is  occupied 
by  the  fold  of  dura  mater  termed  the  falx  cerebri.  Anteriorly 
and  posteriorly,  it  completely  separates  the  cerebral  hemi- 
spheres from  each  other,  but  the  intermediate  part  is  floored 
by  the  corpus  callosum — the  commissural  band  which  passes 
between  the  hemispheres  and  connects  them,  together.  The 
upper  surface  of  the  corpus  callosum  can  be  displayed  by 
gently  drawing  asunder  the  two  sides  of  the  longitudinal 
fissure. 

Dissection. — If  two  brains  are  available,  the  dissector  is  advised,  at  this 
stage,  to  separate  the  cerebrum  from  the  cerebellum,  pons  and  medulla 
oblongata  in  one  of  them,  by  cutting  transversely  through  the  mid  brain  if 
this  has  not  been  done  already.  The  cerebrum  may  then  be  split  in  the 
median  plane  by  placing  a  long  knife  in  the  longitudinal  fissure  and  divid- 
ing, with  one  sweep,  the  various  parts  which  connect  the  two  sides  to  each 
other.  By  this  proceeding,  the  three  surfaces  of  each  cerebral  hemisphere 
are  exposed,  and  the  gyri  and  sulci  can  be  studied  fully  and  satisfactorily. 
If  only  one  brain  is  at  the  disposal  of  the  student,  he  should  not,  at  this  stage, 
separate  the  cerebral  hemispheres  from  each  other,  but  should  endeavour 
to  follow  out  the  gyri  and  sulci  with  the  various  parts  of  the  brain  in 
position.  No  doubt  he  studies  the  hemisphere  in  this  way  at  a  dis- 
advantage, but  as  the  dissection  proceeds,  opportunities  will  occur  which 
will  enable  him  to  examine  those  districts  of  the  surface  which  he  can  see 
only  imperfectly  at  present. 

Cerebral   Gyri  and   Sulci. — The   surfaces  of  the  cerebral 


THE  CEREBRUM  461 

hemispheres  are  rendered  highly  irregular  by  the  presence  of 
gyri,  separated  from  one  another  by  intervening  furrows, 
termed  sulci  and  fissures.  The  surface  pattern  which  is  pre- 
sented by  these  gyri  and  sulci  is,  in  its  general  features,  the 
same  in  all  human  brains ;  but  when  the  comparison  is 
pushed  into  more  detail  many  differences  become  manifest, 
not  only  in  the  brains  of  different  individuals  but  also  in 
the  two  cerebral  hemispheres  of  one  individual. 

Of  the  furrows  two  varieties  must  be  recognised,  viz., 
complete  and  incomplete.  The  complete  fisstires  are  few  in 
number  and  they  consist  of  inwardly  directed  folds  which 
involve  the  whole  thickness  of  the  cerebral  wall.  They  con- 
sequently show  in  the  interior  of  the  cerebral  cavity  or  lateral 
ventricle  in  the  form  of  elevations  on  its  walls.  In  this 
category  are  included  (i)  the  hippocampal  fissure;  (2)  the 
anterior  portion  of  the  calcarine  fissure;  and  (3)  a  portion  of 
the  collateral  fissure.  The  incomplete  Jissures  and  the  sulci  are 
merely  furrows  of  varying  depth  which  do  not  produce  any 
effect  on  the  surface  of  the  ventricular  walls. 

General  Structure  of  the  Cerebral  Hemispheres. — Each 
cerebral  hemisphere  is  composed  of  an  outside  coating  of 
grey  matter,  spread  in  a  continuous  and  uninterrupted  layer 
over  its  surface,  and  an  internal  core  of  white  matter.  The 
grey  coating  is  termed  the  cerebral  cortex^  whilst  the  v.'hite 
internal  part  is  called  the  medullary  centre.  Each  gyrus 
shows  a  corresponding  structure.  It  has  an  external 
covering  of  grey  matter  supported  upon  a  core  of  white 
medullary  matter.  But,  in  addition  to  the  grey  matter  on  the 
outside,  there  are  certain  large  deposits  of  grey  matter  em- 
bedded in  the  substance  of  each  hemisphere  in  its  basal  part. 
These  constitute  the  basal  nuclei,  and  although  to  a  certain 
extent  they  are  isolated  from  the  grey  matter  on  the  surface, 
nevertheless,  at  certain  points,  they  are  directly  continuous 
with  it. 

By  means  of  the  gyri  and  sulci  the  grey  matter  on  the 
surface  of  the  hemisphere  is  increased,  and  its  close 
association  with  the  vascular  pia-mater  is  maintained  without 
any  unnecessary  increase  of  the  bulk  of  the  organ.  The 
vascular  pia-mater  dips  into  every  fissure  and  sulcus,  and 
opportunity  is  therefore  afforded  for  the  cortical  vessels  to 
break  up  into  twigs  of  exceeding  fineness  before  they 
enter   the   substance   of   the   hemisphere.     The    distribution 


462 


THE  BRAIN 


of  the   blood   to   the   grey   cortex    is    in    this   way   rendered 
uniform. 

Cerebral  Lobes  and  Interlobar  Fissures. — Certain  of  the 
fissures  which  traverse  the  surface  of  the  cerebrum  are 
arbitrarily  chosen  for  the  purpose  of  subdividing  the  surface 
into  districts,  termed  lobes.  These  fissures,  which  receive 
the  name  of  interlobar^  are  the  following — (i)  the  lateral 
fissure  (O.T.  Sylvian);  (2)  the  central  (O.T.  fissure  of 
Rolando) ;  (3)  the  parieto-occipital ;  (4)  the  collateral ;  and 
(5)  the  circular  sulcus  (O.T.  limiting  sulcus  of  Reil). 


Post-central  sulcus 
Central  sulcus 
Sulcus  cinguli 


Upper  praecentral  sulcus 

Lower  praecentral  sulcus 
frontal 


Ramus 


Parieto 

occipital  fis 

Ramus  occi 

pitali: 

rans.  occip. 

sulcus 
ost-parietal 

gyrus 


frontal  sulcus 


temp. 
Pre-occipital  notch 


Fis.  lat.  ramus 

ant.  horiz. 

lat.  ram.  ant. 

Pars  triangularis 
rs  orbitalis 
basilaris 

Post,  ramus  of  lateral  fissure 


Lateral  occip.  sulcus 

Fig.  186. — Gyri  and  Sulci  on  the  Lateral  Surface  of  the  Cerebral  Hemisphere. 

The  lobes  which  are  mapped  out  by  these  fissures  are — 
(i)  the  frontal;  (2)  the  parietal;  (3)  the  occipital;  (4)  the 
temporal;  (5)  the  insula.  To  these  may  be  added  a  sixth 
lobe,  in  no  way  related  to  the  interlobar  fissures,  viz.,  the 
olfactory  lobe. 

Lateral  Fissure  (O.T.  Sylvian). — This  is  the  most  con- 
spicuous fissure  on  the  surface  of  the  cerebrum.  It  is 
composed  of  a  short  main  stem,  from  the  lateral  extremity  of 
which  three  branches  radiate.  The  stem  is  placed  on  the 
inferior  surface  of  the  cerebrum  (Fig.  182).  It  begins  at 
the  substantia  perforata  anterior.  Thence  it  passes  laterally, 
forming  a  deep  cleft  between  the  temporal  pole  and  the 
orbital  surface  of  the  frontal  lobe.      Appearing  on  the  lateral 


THE  CEREBRUM  463 

surface  of  the  cerebrum  the  lateral  fissure  immediately 
divides  into  three  radiating  branches.  These  are — (i)  the 
ramus    posterior ;  (2)  the    ramus    anterior   horizontalis ;  and 

(3)  the  ramus  anterior  ascendens. 

The.  posterior  ramus  (Fig.  186)  is  the  longest  and  the  most 
important  of  the  three.  It  extends  posteriorly,  with  a  shght 
upward  inclination,  for  a  distance  of  three  inches  or  more, 
between  the  frontal  and  parietal  lobes,  which  lie  above  it,  and 
the  temporal  lobe,  which  is  placed  below  it.  Finally,  it 
comes  to  an  end  by  turning  upwards  into  the  parietal  lobe  in 
the  form  of  an  ascending  termifial piece  (Fig.  186). 

The  a?tferior  horizontal  limb  (Fig.  186)  extends  anteriorly  in 
the  frontal  lobe,  for  a  distance  of  about  three-quarters  of 
an  inch,  immediately  above  and  parallel  to  the  posterior 
part  of  the  superciliary  margin  of  the  hemisphere. 

The  anterior  ascending  li?nl?  (Fig.  186)  proceeds  upwards, 
with  a  slight  anterior  inclination,  into  the  lower  part  of  the 
lateral  surface  of  the  frontal  lobe  for  a  distance  of  about  an 
inch.  In  many  cases  the  two  anterior  limbs  spring  from  a 
common  stem  of  variable  length  (Fig.  186). 

Sulcus  Circularis  (O.T.  Limiting  Sulcus  of  Reil). — If  the 
lips  of  the  posterior  branch  of  the  lateral  fissure  are  now 
gently  pulled  asunder,  the  insula  (O.T.  island  of  Reil)  will  be 
seen  at  the  bottom.  This  is  surrounded  by  a  circular  sulcus 
which  is  separable  into  three  parts,  viz.,  an  upper  part 
bounding  the  insula  above,  a  lower  part  marking  it  off  below, 
and  an  anterior  part  limiting  it  anteriorly.  The  insula  thus 
mapped  out  is  somewhat  triangular  in  form. 

Opercula  Insulse. — The  present  is  a  good  time  to  study 
the  manner  in  which  the  insula  is  shut  off  from  the  surface 
of  the  hemisphere.  When  the  lateral  fissure  is  held  widely 
open,  it  will  be  noted  that  the  insula  is  overlaid  by  portions 
of  cerebral  cortex  which  appear  as  if  they  were  undermined. 
These  by  the  approximation  of  their  margins  or  lips  form  the 
three  branches  of  the  lateral  fissure,  and  are  termed  the 
opercula  insulcE.  The  opercula  are  four  in  number,  and  are 
named — (i)    temporal,   (2)    fronto- parietal,    (3)  frontal,    and 

(4)  orbital.      They  are  easily  distinguished. 

The  temporal  operculum  extends  upwards  over  the  insula 
from  the  temporal  lobe  ;  it  forms  the  lower  lip  of  the  posterior 
branch  of  the  lateral  fissure. 

The  fronto-parietal  operculum  is  carried   downwards  over 


464  THE  BRAIN 

the  insula  to  meet  the  temporal  operculum.  Its  margin 
forms  the  upper  lip  of  the  posterior  branch  of  the  lateral 
fissure. 

Th.Q  frontal  operculum  (Fig.  186)  is  the  small  triangular 
piece  of  cerebral  cortex  between  the  anterior  ascending  and 
horizontal  branches  of  the  lateral  fissure.  It  is  sometimes 
termed  \k\^  pars  triangularis. 

The  orbital  operculum  (Fig.  186)  is  for  the  most  part  on 
the  under  surface  of  the  hemisphere.  It  lies  below  the 
anterior  horizontal  limb  of  the  lateral  fissure,  and  passes 
posteriorly  from  the  orbital  aspect  of  the  frontal  lobe  over 
the  anterior  part  of  the  insula. 

Sulcus  Centralis  (O.T.  Fissure  of  Rolando). — The  central 
sulcus  takes  an  oblique  course  across  the  lateral  surface 
of  the  cerebral  hemisphere  (Fig.  186).  Its  upper  end  in 
many  cases  cuts  the  supero-medial  border  of  the  hemisphere 
a  short  distance  posterior  to  the  mid-point  between  the 
frontal  and  occipital  poles,  whilst  its  lower  end  terminates 
above  the  middle  of  the  posterior  branch  of  the  lateral  fissure. 
When  its  superior  extremity  turns  round  the  supero-medial 
border  of  the  hemisphere  it  is  continued  posteriorly, 
for  a  short  distance,  on  the  medial  surface  (Fig.  187). 
Although  in  its  general  direction  the  sulcus  centralis  is 
oblique,  it  is  far  from  being  straight.  Nearer  to  its  upper 
than  to  its  lower  end  it  is  bent  posteriorly  so  as  to  form  a 
bay,  within  which  is  accommodated  a  portion  of  the  cerebral 
cortex  which  represents  the  motor  area  of  the  opposite  upper 
limb.  The  upper  and  lower  limits  of  this  bay  are  termed 
the  upper  and  lower  genua  of  the  fissure. 

Fissura  Parieto  -  occipitalis. — The  greater  part  of  this 
fissure  is  situated  on  the  medial  surface  of  the  cerebral  hemi- 
sphere (Fig.  187);  only  a  very  small  part  appears  on  the 
lateral  face  (Fig.   186). 

The  lateral  part  of  the  parieto-occipital  fissure  (O.T.  external 
parieto -occipital)  cuts  the  supero-medial  border  of  the  hemi- 
sphere, in  a  transverse  direction,  from  one  and  a  half  to  two 
inches  anterior  to  the  occipital  pole.  It  is  usually  not  more 
than  half  an  inch  in  length,  and  it  is  brought  to  an  abrupt 
termination  by  an  arching  convolution  which  winds  round  its 
extremity,  and  receives  the  convenient  name  of  arcus  parieto- 
occipitalis  (Fig.  186). 

The  medial  part  of  the  parieto-occipital  fissure  (Fig.    187) 


THE  CEREBRUM 


465 


passes  downwards,  in  a  nearly  vertical  direction,  on  the  medial 
surface  of  the  hemisphere,  as  a  conspicuous  and  deep  cleft, 
which,  at  its  lower  end,  joins  the  calcarine  fissure. 

Fissura  Collateralis  (Fig.  187). — The  collateral  fissure  is  a 
strongly  marked  fissure  on  the  tentorial  part  of  the  inferior 
surface  of  the  cerebral  hemisphere.  It  begins  near  the 
occipital  pole,  and  extends  anteriorly  towards  the  temporal 
pole.     Posteriorly  it  lies  below  and  parallel  to  the  calcarine 

Central  sulcus 


Callosal  sulcus 


Parieto-occipital 
fissure 


Sulcus  cinguli  (O.i. 
Calloso-marginal) 
Genu  of  corpus  callosum 

Septum  pellucidum 

Anterior  commissure      I 

Fornix 


Calcarine  fissure 

Sul3parietal  sulcus 
\  \  \       Stern  of  calcarine  fissure 

\  \  Splenium  of  corpus  callosum 

^         \  Isthmus 

\  Inferior  temporal  sulcus 

Collateral  fissure 


Mamillary  body 


Fig.  187. — The  Gyri  and  Sulci  on  the  Medial  and  Tentorial 
Aspects  of  the  Cerebral  Hemisphere. 


fissure,  whilst  anteriorly  it  is  separated  from  the  hippocampal 
fissure  by  the  hippocampal  gyrus,  which  is  the  highest  and 
most  medial  convolution  on  the  tentorial  part  of  the  inferior 
surface  of  the  hemisphere  (Fig.  187). 

Anterior  to  the  collateral  fissure  a  shallow  sulcus  turns 
round  the  anterior  end  of  the  temporal  lobe  and  intervenes 
between  the  temporal  pole  and  the  uncinate  or  hook-like 
extremity  of  the  hippocampal  gyrus.  This  is  the  incisura 
te}nporalis  or  ecto-rhinal  fissure  (Fig.  188). 

Sulcus  Cinguli  (O.T.  Calloso  marginal  Fissure)  (Fig.  187). 
— This  is  a  strongly  marked  sulcus  on  the  anterior  part  of 

VOL.    II — 30 


466 


THE  BRAIN 


the  medial  surface  of  the  hemisphere.  It  commences  on  the 
lower  portion  of  the  anterior  part  of  the  medial  surface,  curves 
first  upwards  and  then  posteriorly.  Finally,  turning  upwards, 
it  cuts  the  supero-medial  border  of  the  hemisphere  a  short 
distance  behind  the  upper  end  of  the  sulcus  centralis,  and 
terminates  on  the  lateral  surface  of  the  parietal  lobe.  It 
separates  the  anterior  portion  of  the  medial  surface  into  a 
marginal  and  a  central  area.  The  central  part  is  the  gyrus 
cinguli  (O.T.  callosal  gyrus).  The  marginal  part  is  separ- 
ated into  two  portions  by  a  branch  of  the  sulcus  cinguli,  which 
projects  upwards  above  the  middle  of  the  corpus  callosum. 
The  anterior  part  is  the  m.edial  area  of  the  superior  frontal 
gyrus  ;  the  posterior  part  is  the  paracentral  lobule. 

Boundaries  of  the  Frontal  Lobe. 
of  the  cerebral  lobes.  On  the  lateral  surface  of  the  hemisphere 
it  is  bounded  posteriorly  by  the  central  sulcus,  and  below  by 
the  posterior  branch  of  the  lateral  fissure.  On  the  medial 
surface  it  is  limited  by  the  sulcus  cinguli ;  whilst  on  the  inferior 
surface  of  the  hemisphere  the  stem  of  the  lateral  fissure 
forms  its  posterior  boundary. 

Lateral  Surface  of  the  Frontal  Lobe. — On  the  lateral 
surface  of  the  frontal  lobe  the  following  sulci  and  gyri  may  be 
recognised  : — 


The  frontal  is  the  largest 


/'Sulcus    prsecentralis    in- 
ferior. 
Sulcus    prsecentralis    su- 
perior, 
q  1  •  I  Sulcus  paramedians. 

Sulcus  frontalis  superior. 
Sulcus  frontalis  medius. 
Sulcus  frontalis  inferior. 
Sulcus  diagonalis. 
^Sulcus  fronto-marginalis. 


Gyri  < 


Gyrus  centralis  anterior. 
Gyrus  front- /Pars  superior, 
alls  superior\  Pars  inferior. 
Gyrus  front- /Pars  superior, 
alis    medius  \  Pars  inferior. 

f  Pars  basilaris. 
Gyrus  front-J  Pars  triangu- 
alis  inferior.  I      laris. 

[Pars  orbitalis. 


Sulcus  Prcecentralis  Inferior  (Fig.  i86). — The  inferior  prae- 
central  sulcus  consists  of  a  vertical  and  a  horizontal  part, 
and,  when  present  in  a  well-marked  form,  it  presents  a  figure 
like  the  letter  T  or  F.  The  vertical  portion  lies  anterior  to 
the  lower  part  of  the  central  sulcus  (O.T.  fissure  of  Rolando), 
and  the  horizontal  portion  extends  antero-superiorly  into  the 
middle  frontal  gyrus. 

Sulcus  Prcecentralis  Superior  (Fig.  i86). — This  is  a  short 
vertical  sulcus  which  lies  anterior  to  the  upper  part  of  the 


THE  CEREBRUM  467 

central  sulcus.  It  is  almost  invariably  connected  with  the 
posterior  end  of  the  superior  frontal  sulcus. 

Gyrus  Centralis  Anterior. — The  anterior  central  gyrus  is  a 
long  continuous  gyrus  which  is  limited  anteriorly  by  the  two 
praecentral  sulci,  and  posteriorly  by  the  central  sulcus.  It 
extends  obliquely  across  the  hemisphere,  from  the  supero- 
medial  margin  above  to  the  posterior  branch  of  the  lateral 
fissure  below  (Fig.  186). 

Sulcus  Frontalis  Superior  (Fig.  186). — The  superior  frontal 
sulcus  extends  anteriorly  from  the  sulcus  prsecentralis  superior. 

Gyrus  Frontalis  Superior  (Figs.  186,  187). — The  superior 
frontal  gyrus  lies  above  the  superior  frontal  sulcus  and  passes 
round  the  supero-medial  border  on  to  the  medial  surface 
of  the  hemisphere.  It  terminates  anteriorly  in  the  frontal 
pole. 

Sulcus  Frontalis  Inferior  (Fig.  186). — This  lies  at  a  lower 
level  than  the  superior  sulcus  of  the  same  name.  The  posterior 
end  of  the  inferior  frontal  sulcus  is  placed  in  the  angle 
between  the  vertical  and  horizontal  parts  of  the  inferior 
praecentral  sulcus,  and  is  not  infrequently  confluent  with  one 
or  other  of  these.  It  passes  anteriorly  towards  the  superciliary 
margin  of  the  hemisphere,  and  ends  a  short  distance  from 
it  in  a  terminal  bifurcation. 

Gyrus  Frontalis  Medius  (Fig.  186). — The  middle  frontal 
gyrus  is  the  broad  convolution  which  lies  between  the  superior 
and  inferior  frontal  sulci. 

Gyrus  Frontalis  Inferior  (Y'lg.  186). — The  inferior  frontal 
gyrus  is  that  portion  of  the  lateral  surface  of  the  frontal  lobe 
which  is  placed  anterior  to  the  inferior  praecentral  sulcus  and 
below  the  inferior  frontal  sulcus. 

The  stdcus  paramedians  is  the  term  applied  to  a  series  of  short 
irregular  furrows  arranged  longitudinally,  close  to  the  supero-medial  border 
of  the  hemisphere.  These  rudimentary  sulci  partially  subdivide  the  superior 
frontal  gyrus  into  an  upper  and  lower  division,  and  are  of  interest  in  so 
far  that  they  are  best  marked  in  high  types  of  brain. 

The  juiddle  frontal sidcus  (Fig.  186)  lies  horizontally  in  the  anterior  part 
of  the  middle  frontal  gyrus,  and  divides  it  into  an  upper  and  a  lower 
part  (Fig.  186).  As  it  approaches  the  superciliary  margin  of  the  hemi- 
sphere it  bifurcates,  and  its  terminal  branches  spread  out  widely  from  each 
other,  and  together  constitute  a  transverse  furrow  called  the  sidcus  fronto- 
inarginalis. 

Owing  to  the  subdivision  of  the  superior  and  middle  frontal  gyri  in  the 
manner  indicated,  the  gyri  in  the  anterior  part  of  the  lateral  surface  of  the 
frontal  lobe  are  arranged  in  five  horizontal  tiers. 


468 


THE  BRAIN 


Gyrus  Frontalis  Inferior.  —  The  inferior  frontal  gyrus 
possesses  a  special  interest  and  importance,  on  account 
of  the  supposed  localisation  within  it,  on  the  left  side,  of  the 


Longitudinal  fissure 


Olfactory  sulcus 


Olfactory  bulb^ 


Orbital  sulcus.  / 


Olfactory  tract- 
Temporal  pole — . 


Incisura 
temporalis 


Inferior   .| 
temporal 
sulcus 


Collateral 
fissure 


Calcarine 


Fig.  li 


Longitudinal  fissure 

-Gyri  and  Sulci  on  the  Tentorial  and  Orbital  Surfaces  of  the 
Cerebral  Hemispheres. 


speech-centre.  It  consists  of  an  upper  non-opercular  and  a 
lower  opercular  portion.  The  latter  is  cut  up  into  three  parts 
by  the  two  anterior  branches  of  the  lateral  fissure.     These 


THE  CEREBRUM  469 

are  termed  the  pars  basilaris,  the  pars  triangularis,  and  the 
pars  orbitaHs. 

The  pars  basilaris  (Fig.  186)  is  that  part  which  lies  be- 
tween the  vertical  limb  of  the  inferior  prgecentral  sulcus  and 
the  anterior  ascending  ramus  of  the  lateral  fissure.  It  forms 
the  anterior  portion  of  the  fronto-parietal  operculum,  and  it 
is  traversed  in  an  oblique  direction  by  a  shallow  furrow, 
termed  the  sulcus  dlago?ialls. 

The  pars  triangularis  (Fig.  186)  is  simply  another  name 
for  the  frontal  operculum.  It  is  triangular  in  form,  and  lies 
between  the  anterior  ascending  and  anterior  horizontal  rami 
of  the  lateral  fissure. 

The  pars  orbitalls  (Fig.  186)  is  placed  below  the  anterior 
horizontal  ramus  of  the  lateral  fissure. 

Medial  Surface  of  the  Frontal  Lobe. — On  this  aspect  of 
the  frontal  lobe  is  the  elongated,  more  or  less  continuous, 
medial  part  of  the  superior  frontal  gyrus  (O.T.  marginal 
gyrus).  It  lies  between  the  supero-medial  border  of  the 
hemisphere  and  the  sulcus  cinguli  (Fig.  187). 

In  the  anterior  part  of  this  gyrus  one  or  two  curved  sulci  are  usually 
present.     These  are  termed  the  sulci  rostrales. 

The  posterior  end  of  the  medial  surface  of  the  superior 
frontal  gyrus  is  more  or  less  completely  cut  off  from  the 
anterior  part.  It  forms  part  of  the  paracentral  lobule^  and 
lies  anterior  to  the  upper  end  of  the  central  sulcus  (Fig.  187). 

Orbital  Surface  of  the  Frontal  Lobe. — On  this  aspect  of 
the  frontal  lobe  there  are  two  sulci — viz.  the  olfactory  and 
the  orbital. 

Sulcus  Olfactorius. — The  olfactory  sulcus  (Fig.  188)  is  a 
straight  furrow  which  runs  parallel  to  the  medial  orbital 
border  of  the  hemisphere.  It  is  occupied  by  the  olfactory 
tract  and  bulb,  and  it  cuts  off  a  narrow  strip  of  the  orbital 
surface  close  to  the  medial  border  which  receives  the  name 
oi  gyrus  rectus  (Fig.  188). 

The  orbital  sulcus  is  a  compound  furrow  which  assumes 
many  different  forms.  Most  frequently  it  takes  the  shape  of 
the  letter  H,  of  which  the  three  component  parts  are  a 
lateral  limb,  a  medial  limb,  and  a  transverse  limb. 

The  lateral  limb  curves  round  the  orbital  part  of  the 
inferior  frontal  gyrus,  and  limits  it  medially.  The  medial 
limb  marks  off  a  convolution  between  itself  and  the  olfactory 


470  THE  BRAIN 

sulcus  which  receives  the  name  of  gyrus  orbitalis  medialis. 
The  transverse  limb  takes  a  curved  course  with  the  concavity 
directed  posteriorly.  It  divides  the  district  between  the 
lateral  and  medial  limbs  into  an  anterior  part,  or  gyrus  orbitalis 
anterior^  and  a  posterior  part,  or  gyrus  orbitalis  posterior.  The 
latter  corresponds  with  the  greater  part  of  the  orbital  oper- 
culum. 

Boundaries  of  the  Parietal  Lobe. — The  parietal  lobe  forms 
a  considerable  part  of  the  lateral  surface  of  the  cerebral  hemi- 
sphere, and  it  appears  also  on  the  medial  face,  where  it  forms 
the  prsecuneus  and  the  posterior  part  of  the  paracentral 
lobule.  Anteriorly^  it  is  bounded  by  the  central  sulcus, 
which  separates  it  from  the  frontal  lobe.  Below,  it  is 
bounded  in  the  anterior  part  of  its  extent  by  the  posterior 
branch  of  the  lateral  fissure.  Posterior  to  the  upturned  end 
of  that  fissure,  it  is  quite  continuous  inferiorly  with  the 
temporal  lobe,  and  an  arbitrary  line  drawn  posteriorly  on  the 
surface  of  the  brain  in  continuation  of  the  posterior  branch 
of  the  lateral  fissure  is  taken  as  its  inferior  limit  (Fig.  i86). 
Posteriorly,  it  is  separated  from  the  occipital  lobe,  at  the  supero- 
medial  border  of  the  hemisphere,  by  the  lateral  part  of  the 
parieto-occipital  fissure.  Below  that  it  is  more  or  less  directly 
continuous  with  the  occipital  lobe,  but  an  arbitrary  line 
drawn  across  the  lateral  surface  of  the  hemisphere  from  the 
extremity  of  the  parieto-occipital  fissure  to  an  indentation 
on  the  infero-lateral  border  of  the  hemisphere,  termed  the 
prce-occipital  notch,  may  be  regarded  as  furnishing  a  posterior 
limitation.  The  prae-occipital  notch  is,  as  a  rule,  visible  only 
in  brains  that  have  been  hardened  in  situ.  It  is  produced 
by  a  slight  wrinkle  or  fold  of  the  dura  mater,  on  the  deep 
aspect  of  the  parieto-mastoid  suture  and  in  relation  to  the 
portion  of  the  lateral  venous  sinus  which  lies  in  this  locality. 
The  notch  is  placed  on  the  infero-lateral  border  of  the  hemi- 
sphere, about  one  inch  and  a  half  anterior  to  the  occipital 
pole. 

Medial  Surface  of  the  Parietal  Lobe — Prsecuneus  and 
Posterior  Part  of  Paracentral  Lobule.  —  On  the  medial 
surface  of  the  hemisphere  the  parietal  lobe  is  represented 
by  the  prcBCuneus  and  the  posterior  part  of  the  paracentral 
lobule.  This  district,  which  is  somewhat  quadrilateral  in  form, 
lies  between  the  upper  end  of  the  central  sulcus  and  the 
medial  part  of  the  parieto-occipital  fissure.      Below,  it  is  im- 


THE  CEREBRUM 


471 


perfectly  separated   from   the   gyrus   cinguli    by  a  somewhat 
variable  sulcus  called  the  sub -parietal  sulcus  (Fig.  187). 

Lateral  Surface  of  the  Parietal  Lobe. — The  gyri  and 
sulci  on  the  lateral  surface  of  the  parietal  lobe  are  the 
following : — 


r  Posterior  central. 

Superior  parietal  lobule. 
Gyri-  Inferior  /Supra-marginal. 

parietal-  Angular, 
l^lobule.    [Postparietal. 


Sulci  <! 


'Sulcus    postcentralis 
Inter-  inferior, 

parietal  J  Sulcus    postcentralis 

of        I      superior. 
Turner.      Ramus  horizontalis. 

^  Ramus  occipitalis. 
Upturned  ends  of — 

(a)  Posterior     branch      of 

lateral. 
{h)  Superior  temporal. 
{c)  Middle  temporal. 


Interparietal  Sulcus  of  Turner. —  This  is  a  composite 
sulcus  built  up  of  four  originally  distinct  factors.  Two  of 
these,  termed  the  sulcus  postcentralis  inferior  and  the  sulcus 
postcentralis  superior,  take  a  more  or  less  vertical  course 
across  the  hemisphere,  and  are  frequently  continuous  with 
each  other.  The  other  two  factors  are  placed  horizontally, 
one  posterior  to  the  other,  and  they  are  called  the  ramus 
horizontalis  and  the  ramus  occipitalis. 

The  sulcus  postcentralis  inferior  lies  posterior  to  the  lower 
part  of  the  central  sulcus  (O.T.  Rolando),  whilst  the  sulcus 
postcentralis  superior  occupies  a  similar  position  in  relation 
to  the  upper  part  of  that  sulcus.  When  confluent  with  each 
other  they  form  a  long  continuous  furrow,  which  stretches 
across  the  hemisphere,  posterior  and  parallel  to  the  central 
sulcus  (Fig.  186). 

The  ra?nus  horizontalis  (Fig.  186)  is  continuous  with  the 
upper  end  of  the  sulcus  postcentralis  inferior,  and  extends 
posteriorly,  with  a  slight  inclination  upwards,  between  the 
superior  parietal  lobule  above  and  the  inferior  parietal  lobule 
below.  With  the  two  confluent  postcentral  sulci  it  presents  a 
figure  like  the  letter  — |  placed  on  its  side. 

The  ramus  occipitalis  (Fig.  186)  is  a  curved  sulcus.  It 
forms  the  lateral  boundary  of  the  arcus  parieto-occipitalis, 
which  surrounds  the  lateral  part  of  the  parieto-occipital  fissure. 
Sometimes  the  ramus  occipitalis  is  linked  on  to  the  ramus 
horizontalis  —  more  frequently  it  is  separate.  Its  posterior 
end  runs  into  the  occipital  lobe,  and,  posterior  to  the  arcus 


472  THE  BRAIN 

parieto- occipitalis,  it  bifurcates  into  two  widely  spread-out 
branches.  These  form  a  short  transverse  fissure  in  the 
occipital  lobe,  termed  the  sulcus  occipitalis  transversus  (Ecker) 
(Fig.  1 86). 

The  upturned  ends  of  the  posterior  branch  of  the  lateral 
fissure,  of  the  superior  temporal  sulcus  and  of  the  middle 
temporal  sulcus  (Fig.  i86)  extend  for  a  short  distance,  one 
posterior  to  the  other,  into  the  inferior  parietal  lobule. 

Gyri  on  the  Lateral  Surface  of  the  Parietal  Lobe. — The 
interparietal  sulcus  maps  out  three  districts  or  areas  on  the 
lateral  surface  of  the  parietal  lobe.  These  are  the  posterior 
central  gyrus  and  the  superior  and  inferior  parietal  lobules. 

The  gyrus  centralis  posterior  (Fig.  i86)  is  a  long  gyrus 
which  extends  obliquely  across  the  hemisphere  from  the  supero- 
medial  border  above  to  the  posterior  branch  of  the  lateral 
fissure  below.  Anteriorly,  it  is  bounded  by  the  central 
sulcus,  and  posteriorly,  by  the  superior  and  inferior  postcentral 
sulci. 

The  superior  parietal  lobule  is  the  area  of  cerebral  cortex 
which  lies  between  the  ramus  horizontalis  below  and  the 
supero-medial  border  of  the  hemisphere  above.  It  is  bounded 
anteriorly  by  the  superior  postcentral  sulcus ;  and  posteriorly, 
it  is  connected  with  the  occipital  lobe  by  the  arcus  parieto- 
occipitalis.  It  is  continuous  around  the  supero-medial  border 
of  the  hemisphere  with  the  prsecuneus. 

The  inferior  parietal  lobule  lies  below  the  ramus  horizon- 
talis and  the  ramus  occipitalis,  and  posterior  to  the  inferior 
postcentral  sulcus.  It  is  more  or  less  directly  continuous 
with  the  occipital  lobe  posteriorly  and  with  the  temporal 
lobe  below.  It  presents  three  arching  gyri,  viz.  the  supra- 
marginal  anteriorly,  the  post-parietal  posteriorly,  and  the 
angular  between  them. 

The  supra-marginal  gyrus  (Fig.  i86)  is  folded  round  the 
upturned  end  of  the  posterior  branch  of  the  lateral  fissure  and 
is  continuous  with  the  superior  temporal  gyrus.  The  angular 
gyrus  (Fig.  i86)  arches  over  the  upturned  end  of  the  superior 
temporal  sulcus,  and  is  continuous  with  the  middle  temporal 
gyrus.  The  post-parietal  gyrus  (Fig.  i86)  winds  round  the 
upturned  end  of  the  middle  temporal  sulcus,  and  runs  into 
the  inferior  temporal  gyrus. 

Boundaries  of  the  Occipital  Lobe. — The  occipital  lobe 
forms    the    posterior   pyramidal   part   of   the   cerebral    hemi- 


THE  CEREBRUM  473 

sphere,  and  it  encloses  the  posterior  horn  of  the  lateral 
ventricle.  On  the  surface  it  is  very  imperfectly  mapped  off 
from  the  parietal  and  temporal  lobes,  which  lie  anterior  to  it. 
It  presents  three  surfaces  and  an  apex  or  occipital  pole.  On 
the  medial  aspect  of  the  hemisphere  it  is  separated  from  the 
parietal  lobe  {i.e.  the  praecuneus)  by  the  parieto-occipital 
fissure.  On  the  tentorial  part  of  the  inferior  surface  it  is  not 
separated  either  from  the  temporal  lobe  or  from  the  gyrus 
hippocampi,  which  lie  anterior  to  it.  It  is  necessary,  there- 
fore, on  this  aspect,  to  employ  an  arbitrary  line  of  demarcation, 
which  extends  from  the  prae-occipital  notch,  on  the  infero- 
lateral  border  of  the  hemisphere,  to  the  isthmus  of  the  gyrus 
fornicatus,  which  lies  below  the  posterior  end  of  the  corpus 
callosum.  On  the  lateral  surface  the  parieto-occipital  fissure, 
and  an  arbitrary  line  from  that  fissure  to  the  prae-occipital 
notch,  may  be  regarded  as  separating  the  occipital  from  the 
parietal  and  temporal  lobes. 

Medial  Aspect  of  the  Occipital  Lobe. — On  the  medial 
surface  are  (i)  the  calcarine  fissure;  (2)  the  cuneus ;  and 
(3)  part  of  the  gyrus  lingualis. 

The  calcarine  fissure  commences  below  the  isthmus  of 
the  gyrus  fornicatus  and  takes  a  curved  course  tow^ards  the 
occipital  pole  where  it  bifurcates  into  short  branches.  At  a 
point  somewhat  nearer  its  anterior  than  its  posterior  extremity 
it  is  joined  by  the  parieto-occipital  fissure  and  the  two  fissures 
together  form  a  >--shaped  figure. 

When  calcarine  and  parieto-occipital  fissures  are  fully  opened  up,  so 
as  to  expose  the  bottom  in  each  case,  two  well-marked  deep  or  submerged 
gyri  will  be  displayed  (Fig.  189).  One  of  these,  the  gyrus  cunei,  marks 
off  the  parieto-occipital  fissure  from  the  calcarine  fissure  ;  the  other  in- 
terrupts the  calcarine  fissure  immediately  posterior  to  its  junction  with 
the  parieto-occipital.  It  is  called  the  anterior  cuneo-lingual  deep  g)'riis, 
and  it  divides  the  calcarine  fissure  into  an  anterior  and  a  posterior  part. 
The  anterior  part  of  the  calcarine  fissure  corresponds  very  nearly  to  the  stem 
of  the  >- -shaped  fissural  arrangement.  It  is  very  deep  and,  being  a 
complete  fissure,  it  gives  rise  to  an  elevation,  called  the  calcar  avis,  on  the 
medial  wall  of  the  posterior  horn  of  the  lateral  ventricle.  The.  posterior  part 
of  the  calcarine  fissure  is  much  shallower. 

The  cuneus  (Fig.  187)  is  the  wedge-shaped  or  triangular 
district  on  the  medial  aspect  of  the  occipital  lobe  between 
the  parieto-occipital  and  calcarine  fissures. 

^\i&  gyrus  lingualis  (Figs.  187,  188)  is  a  well-marked  gyrus 
situated    between    the   calcarine   fissure   above  and  the  pos- 


474  THE  BRAIN 

terior  part  of  the  collateral  fissure  below.  It  commences  at 
the  occipital  pole  and  narrows,  as  it  passes  anteriorly,  to  its 
union  with  the  hippocampal  gyrus.  It  lies  partly  on  the 
medial  surface  and  partly  on  the  tentorial  surface  of  the 
occipital  lobe. 

Tentorial  Surface  of  the  Occipital  Lobe. — On  this  aspect 
lie  part  of  the  gyrus  lingualis  and  the  posterior  part  of  the 
fusiform  gyrus.  They  are  separated  by  the  posterior  part 
of  the  collateral  fissure.  The  gyrus  fusiformis  takes  part, 
anteriorly,  in  the  formation  of  the  temporal  lobe,  and  it  is 
separated  from  the  inferior  temporal  gyrus  by  the  inferior 
temporal  sulcus. 


Praecuneus-^^^^  ^^^^J^^  Gyrus  cinguH 

-Corpus  callosuin 


Medial  parieto-_ 

occipital  fissure  \  IJIiiimiaM  M  \]  ^^^K^M^       rj-,    , 


Cuneus 


Gyrus  cunei 


Anterior  cuneo-_4|(Bi^™^B»i>w  ^.^^^  -    ^bs»»c a«      <-•  r  i- 

1-  1  J  ^M^^BS'  "  Jk     --,.«^ — Gyrus  lingualis 

ungual  deep  gyrus    ^ipifMITr       1,1   "^^^^^^flBfl 

Posterior  cuneo-^/^^VrL^^^^^^^^^^^K---^"terIor  part  of  the 

lingual  deep  gyrus  "Vi^r'^'  ^^^"^"J       calcanne  fissure 

Fig.  189. — Posterior  part  of  medial  surface  of  the  Left  Hemisphere.  The 
calcarine  and  the  parieto-occipital  fissures  are  widely  opened  up  to  show 
the  deep  gyri  within  them. 

Lateral  Surface  of  the  Occipital  Lobe. — There  are  two  well- 
marked  sulci  on  this  surface  of  the  occipital  lobe — viz.  the 
sulcus- occipitalis  transversus  and  the  sulcus  occipitalis  lateralis 
or  sulcus  lunatus  of  Elliot  Smith. 

The  sulcus  occipitalis  transversus  (Fig.  i86)  extends  trans- 
versely across  the  upper  part  of  the  lobe  posterior  to  the  arcus 
parieto- occipitalis.  It  has  already  been  described  as  the 
terminal  bifurcation  of  the  ramus  occipitalis  of  the  inter- 
parietal sulcus. 

The  sulcus  occipitalis  lateralis  (Fig.  i86)  is  a  short 
horizontal  furrow  which  divides  the  lateral  surface  of  the  lobe 
into  an  upper  and  a  lower  area  of  very  nearly  equal  extent. 
These  areas  are  connected  by  means  of  superficial  annectant 
gyri  with  the  parietal  and  temporal  lobes. 


THE  CEREBRUM  475 

Boundaries  of  the  Temporal  Lobe. — The  temporal  lobe  lies 
posterior  to  the  stem  of  the  lateral  fissure  and  below  its 
posterior  branch.  It  presents  an  upper,  a  lateral,  and  a 
tentorial  surface,  with  a  free  apex  or  pole  which  projects 
anteriorly.  Above,  it  is  bounded  by  the  posterior  branch 
of  the  lateral  fissure  together  with  the  artificial  line  drawn 
posteriorly  from  that  fissure.  On  the  tentorial  surface  it  is 
separated  from  the  hippocampal  gyrus  by  the  collateral  fissure  ; 
whilst  posteriorly,  it  is  marked  off  from  the  occipital  lobe  by 
the  arbitrary  lines  described  on  p.  470.  The  apex  or  temporal 
pole  projects  anteriorly  on  the  under  surface  of  the  brain. 
It  should  be  noticed  that  the  recurved  extremity  of  the 
hippocampal  gyrus,  which  lies  to  the  medial  side  of  the 
hemisphere,  does  not  reach  the  temporal  pole,  but  is 
separated  from  it  by  the  incisura  temporalis  or  ectorhinal 
fissure. 

Upper  or  Opercular  Surface  of  the  Temporal  Lobe. — This 
is  the  surface  of  the  temporal  operculum  which  is  opposed  to 
the  insula  and  the  fronto- parietal  operculum.  The  lateral 
fissure  must  therefore  be  widely  opened  up  to  expose  it. 
For  the  most  part  the  surface  is  smooth,  but  towards  its 
posterior  part  there  are  a  few  shallow  furrows,  called  the 
sulci  of  Heschl^  whilst  anteriorly,  also  on  the  deep  aspect  of 
the  temporal  pole,  two  or  three  furrows  are  evident. 

Lateral  Surface  of  the  Temporal  Lobe. — On  this  aspect  of 
the  lobe  there  are  two  horizontal  sulci,  called  the  superior 
and  middle  temporal  sulci. 

The  superior  temporal  sulcus  (Fig.  186)  is  a  long,  continuous 
and  deep  cleft  which  begins  near  the  temporal  pole  and 
proceeds  posteriorly,  below  the  posterior  branch  of  the  lateral 
fissure.  Its  posterior  end  turns  upwards,  into  the  parietal  lobe, 
and  is  surrounded  by  the  angular  gyrus. 

The  middle  te77iporal  sulcus  is  placed  midway  between  the 
superior  temporal  sulcus  and  the  infero-lateral  border  of  the 
hemisphere.  It  is  very  rare  to  find  it  in  the  form  of  a  con- 
tinuous cleft.  Usually  it  is  broken  up  into  several  isolated 
pieces,  placed  one  posterior  to  the  other.  Its  posterior  part 
turns  upwards  into  the  parietal  lobe  (Fig.  186),  where  it  is 
surrounded  by  the  post-parietal  gyrus,  and  lies  close  to  the 
artificial  line  of  demarcation  between  the  occipital  and 
parietal  lobes. 

By  these   two    temporal   sulci   the   lateral   surface   of   the 


476 


THE  BRAIN 


temporal  lobe  is  mapped  out  into  three  tiers  of  horizontal 
gyri,  which  are  termed  the  superior^  inferior^  and  middle 
temporal  gyri  ( Fig.  1 8  6 ). 

Tentorial  Surface  of  the  Temporal  Lobe. — On  this  surface 
there  is  one  fissure,  termed  the  inferior  temporal  sulcus. 

The  inferior  temporal  sulcus  (Fig.  i88)  lies  below  and  lateral 

S.R.^. 


S.R.«. 


S.R./. 


Fig.  190. — Fissures  and  Gyri  on  the  Surface  of  the  Insula. 
( Eberstaller, ) 


T,  2,  and  3.  Three  short  gyri  on  the  frontal 

part  of  the  insula. 
4  and  5.  Two  long  gyri  on  parietal  part. 
S.R.a.  Anterior  part  of  limiting  sulcus. 
S.R.i'.  Superior  part  of  limiting  sulcus. 
S.  R./.   Inferior  part  of  limiting  sulcus. 
L.   Limen  insulae. 
P.   Pole  of  the  insula. 


F.    Orbital  operculum  (for  the  most  part 

removed). 
T.   Temporal  pole. 
Ti.  Superior  temporal  gyrus. 
T2.   Middle  temporal  gyrus. 
x.y.   Gyri  of  Heschl. 
s.i.   Sulcus  centralis  insulae. 
s.a.   Sulcus  praecentralis  insulae. 
in.   Gyri  on  deep  surface  of  temporal  pole. 


to  the  collateral  fissure,  and  close  to  the  infero-lateral  border 
of  the  hemisphere.  It  runs  in  an  antero-posterior  direction 
and  is  not  always  confined  to  the  temporal  lobe,  but  may 
extend  posteriorly  towards  the  occipital  pole.  It  is  usually 
broken  up  into  two  or  more  separate  pieces. 

The  fusiform  gyrus  (Fig.  188)  is  situated  between  the 
collateral  fissure  and  the  inferior  temporal  sulcus.  It  extends 
from  the  occipital  pole  to  the  temporal  pole. 

The   narrow   strip   of   surface   below    and    lateral    to    the 


THE  CEREBRUM  477 

inferior  temporal  sulcus  is  continuous,  round  the  infero-lateral 
margin  of  the  hemisphere,  with  the  inferior  temporal  gyrus 
on  the  lateral  surface  of  the  cerebrum,  and  is  reckoned  as  a 
part  of  it. 

The  three  temporal  gyri  and  the  fusiform  gyrus  run  into  one 
another  at  the  temporal  pole. 

Insula  (O.T.  Island  of  Reil). — The  insula  is  a  triangular 
field  of  cerebral  cortex  which  lies  on  a  deeper  plane  than 
the  general  surface  of  the  hemisphere,  and  is  hidden  from 
view  by  the  four  opercula  which  overlap  it  (p.  463).  It  is 
bounded  by  a  distinct  limiting  sulcus,  sulcus  circularis  (Reil), 
which  has  been  described  already ;  and  its  dependent  apical 
part  or  pole,  which  looks  downwards,  is  in  close  relation  to 
the  stem  of  the  lateral  fissure,  and  to  the  substantia  perforata 
anterior  on  the  base  of  the  brain. 

The  insula  is  divided  into  several  diverging  gyri  by 
a  series  of  radiating  sulci.  Of  the  latter,  one,  which  pre- 
sents the  same  direction  and  lies  in  the  same  plane  as  the 
central  sulcus,  receives  the  name  of  the  sulcus  centralis  instilce. 
It  divides  the  insula  into  an  anterior  frontal  part  and  a 
posterior  parietal  portion. 

Olfactory  Lobe. — The  olfactory  lobe  is  small  and  rudi- 
mentary in  the  human  brain.  It  comprises  (i)  the  olfactory 
bulb  and  tract  with  the  three  striae,  and  (2)  the  trigonum 
olfactorium. 

The  olfactory  tract  is  a  narrow  white  prismatic  band,  which 
expands  anteriorly  into  a  swollen  bulbous  extremity  termed 
the  olfactory  bulb.  Both  the  tract  and  the  bulb  lie  in  the 
olfactory  sulcus  on  the  orbital  surface  of  the  frontal  lobe, 
whilst  the  inferior  surface  of  the  bulb,  when  the  brain  is  in 
position,  rests  on  the  cribriform  plate  of  the  ethmoid  bone 
and  receives  the  numerous  olfactory  nerves  which  reach  it 
through  the  foramina  in  that  part  of  the  cranial  floor. 

Posteriorly,  the  olfactory  tract  divides  into  two  or  three 
diverging  stri^.  The  medial  stria  (O.T.  7fiesial  root)  curves 
abruptly  medialwards,  and  may  be  followed  into  the  extremity 
of  the  gyrus  cinguli  and  the  subcallosal  gyrus.  The  lateral 
stria  (O.T.  lateral  root)  runs  postero  -  laterally  over  the 
lateral  part  of  the  substantia  perforata  anterior,  and  gradually 
disappears  from  view.  In  animals,  in  which  the  olfactory 
apparatus  is  better  developed  than  in  man,  it  may  be 
traced    into    the    uncinate    extremity    of    the    hippocampal 


478  THE  BRAIN 

gyrus.      The  intermediate  stria,  which  is  not  always  present, 
runs  posteriorly  across  the  trigonum  olfactorium. 

The  gyrus  sub-callosus  is  a  narrow  cortical  strip,  of  some  morphological 
importance,  which  lies  on  the  medial  surface  of  the  hemisphere  immediately 
below  the  genu  of  the  corpus  callosum. 

The  trigonum  olfactorium  is  the  little  triangular  field  of 
grey  matter  which  occupies  the  interval  between  the  medial 
and  lateral  strise  of  the  olfactory  tract  at  the  point  where 
they  begin  to  diverge. 

Gyrus  Fornicatus. — This  gyrus,  sometimes  called  the 
limbic  lobe,  is  seen  on  the  medial  and  tentorial  surfaces  of  the 
hemisphere.  It  is  a  ring-like  convolution,  the  extremities  of 
which  approach  each  other  closely  at  the  substantia  perforata 
anterior. 

The  upper  and  anterior  part  of  the  gyrus  fornicatus  lies 
in  intimate  relation  to  the  extremities  and  upper  surface  of 
the  corpus  callosum,  and  it  is  called  the  gyrus  cinguli.  The 
lower  portion  of  the  gyrus  fornicatus  is  termed  the  hippocampal 
gyrus,  and  forms  the  medial  part  of  the  tentorial  portion  of 
the  lower  surface  of  the  hemisphere.  The  continuity  between 
the  hippocampal  gyrus  and  the  gyrus  cinguli  is  established, 
below  the  posterior  end  of  the  corpus  callosum,  by  a  narrow 
portion  of  the  gyrus  fornicatus  called  the  isthmus.  From  this 
point  the  hippocampal  gyrus  extends  anteriorly  towards  the 
temporal  pole.  Finally,  at  the  side  of  the  pedunculus  cerebri, 
the  hippocampal  gyrus  is  folded  on  itself,  and  ends  in  a 
recurved  hook-like  extremity,  termed  the  uncus.  The  uncus 
does  not  reach  the  temporal  pole. 

The  gyrus  cinguli  (O.T.  callosal  convolution)  begins  below 
the  anterior  end  of  the  corpus  callosum  at  the  substantia 
perforata  anterior,  and,  winding  round  the  genu  of  the 
callosum,  it  is  continued  posteriorly  on  its  upper  surface  to 
the  thickened  posterior  extremity  or  splenium.  Finally, 
curving  round  this,  it  becomes  greatly  narrowed  through 
the  calcarine  fissure  cutting  into  it.  This  narrow  part  is 
termed  the  isthmus,  and  constitutes  the  link  of  connection 
between  the  gyrus  cinguli  and  the  hippocampal  gyrus. 

The  gyrus  cinguli  is  separated  from  the  superior  frontal 
gyrus  and  the  paracentral  lobule  by  the  sulcus  cinguli  \ 
from  the  praicuneus  by  the  subparietal  sulcus ;  and  from  the 
lingual  gyrus  by  the  calcarine  fissure.  It  is  separated  from 
the  corpus  callosum  by  the  callosal  sulcus. 


THE  CEREBRUM  479 

The  hippoca77ipal  gy^riis  is  bounded  below  and  laterally  by 
the  anterior  part  of  the  collateral  fissure,  and  anteriorly  by 
the  incisura  temporalis,  which  separates  its  hooked  extremity, 
or  uncus,  from  the  temporal  pole.  Supero -medially  it 
is  limited  by  the  hippocampal  fissure ;  whilst  posteriorly  it 
is  divided  into  two  parts  by  the  anterior  extremity  of  the 
calcarine  fissure.  Of  these,  the  upper  is  the  isthmus,  which 
connects  it  with  the  gyrus  cinguli,  whilst  the  lower  portion 
is  continuous  with  the  gyrus  lingualis. 

If  the  hippocampal  fissure,  which  lies  above  the  hippocampal  g}'rus, 
is  opened  up,  in  a  soft  brain,  the  fascia  dentata  and  the  fimbria  lying  side 
by  side  will  be  brought  into  view.  In  a  hardened  brain  the  examination 
of  this  region  should  be  deferred  (p.  492). 


The  Corpus  Callosum. 

A  dissection  should  now  be  made  with  the  view  of  exposing 
the  upper  surface  of  the  corpus  callosum,  which  is  the  com- 
missural band  connecting  the  cerebral  hemispheres  at  the 
bottom  of  the  longitudinal  fissure. 

Dissection. — With  a  long  knife  slice  off  the  top  of  the  right  hemisphere 
at  the  level  of  the  sulcus  cinguli.  The  white  medullary  centre  of  the 
cerebral  hemisphere,  enclosed  on  all  hands  by  the  grey  cortex,  is  brought 
into  view,  and  the  appearance  receives  the  name  of  centrum  semi-ovale. 
From  the  central  white  mass  medullary  prolongations  proceed  into  all 
the  gyri. 

A  transverse  incision  may  next  be  made  through  the  middle  of  the 
g}TUS  cinguli ;  then  the  anterior  and  posterior  parts  of  the  gyrus  cinguli 
should  be  torn  away  from  the  hemisphere  in  a  lateral  direction.  If  this 
is  done  successfully  the  manner  in  which  the  fibres  of  the  corpus 
callosum  enter  the  hemisphere  will  be  seen.  In  cases  where  the  student 
is  dissecting  the  brain  for  the  second  time  the  knife  should  not  be  used 
at  all  in  carrying  out  this  dissection.  The  top  of  the  hemisphere  down 
to  the  level  of  the  sulcus  cinguli  should,  in  the  first  instance,  be  torn  oft", 
and  then  the  gyrus  cinguli  may  be  treated  in  the  same  way.  By  this 
expedient  the  fibres  of  the  corpus  callosum  may  be  traced  into  the  g}'ri. 

Cingulum. — If  the  deep  surface  of  the  gyrus  cinguli, 
which  has  been  torn  away,  is  examined,  a  large  bundle  of 
longitudinally  directed  fibres  will  be  noticed  embedded  in  its 
substance.  This  is  the  cingulum.  It  can  be  easily  dislodged  ; 
a  very  slight  degree  of  traction  is  all  that  is  required  to 
lift  it  out  of  its  bed.  It  begins  anteriorly  at  the  substantia 
perforata  anterior,  curves  round  the  convexity  of  the  corpus 
callosum,  and  then  descends,  round  its  posterior  end,  and 
terminates   in   the  hippocampal   gyrus.      The  cingulum   is  a 


48o 


THE  BRAIN 


long  association  bundle  composed  of  several  systems  of  fibres 
which  run  only  for  short  distances  within  it.  It  is  closely 
associated  with  the  gyrus  fornicatus. 


Dissection. — The  gyri  and  sulci  on  the  medial  surface  of  the  left  hemi- 
sphere may  now  be  studied,  and  then  the  dissection,  which  has  been 
carried  out  with  the  view  of  exposing  the  corpus  callosum,  may  be  repeated 


Cingulum 


Fibres  of  corona  radiata 


Intersection  of 
callosal  and  corona  , 
radiata  systems  of  1 
fibres  1^ 


Frontal  fibres 
,  Genu 

'  Cut  surface 


Corpus  callosum 


Transverse  fibres 
of  corpus 
callosum 


Cingulum 


\  Inferior  longitu- 
dinal fasciculus 


Tapetum 


Splenium 


Forceps  major 
Stria  longitudinalis  medialis 


Fig.  191. — The  Corpus  Callosum  exposed  from  above  and  the  right  half 
dissected  to  show  the  course  taken  by  the  fibres. 

on  the  left  side.  In  doing  this,  however,  take  care  not  to  injure  the  medial 
surface  of  the  left  hemisphere  posterior  to  the  parieto  -  occipital  fissure. 
Indeed,  an  effort  should  be  made  to  preserve  that  fissure  intact,  so  that  it 
and  the  cuneus  may  be  studied  afterwards,  on  this  side,  in  connection  with 
the  gyri  and  sulci  on  the  under  surface  of  the  hemisphere. 

The  upper  surface  of  the  corpus  callosum  is  now  exposed,  and  it  will 
be  seen  that  it  unites  into  one  mass  the  medullary  centres  of  the  two 
hemispheres.  The  continuous  white  field,  consisting  of  the  corpus  callosum 
and  the  medullary  centre  of  each  hemisphere,  receives  the  name  of 
centrum  ovale. 


Corpus  Callosum. — This  is  the  great  transverse  commissure 


THE  CEREBRUM 


481 


of  the  cerebrum.  It  is  placed  nearer  the  anterior  than  the 
posterior  end  of  the  brain,  and  it  unites  the  medial  surfaces  of 
the  two  cerebral  hemispheres  throughout  very  nearly  a  half  of 
their  antero-posterior  length. 

Its  upper  surface  is  convex  antero-posteriorly  and  concave 
from  side  to  side,  and  it  forms  the  bottom  of  the  longitudinal 
fissure.  On  each  side  of  the  fissure  it  is  covered  by  the 
gyrus  cinguli  (O.T.  callosal  gyrus).     Only  in  its  posterior  part 


II  10  9  8  7 

Fig.   192. — Median  section  through  the  Brain. 


1.  Fornix.                                [  6.  Corpora  quadrigemina. 

2.  Tela  chorioidea.  7.  Ant.  niedullarj^  velum. 

3.  Pineal  body.  8.  Aquaeductus  cerebri. 

4.  Vena  magna  cerebri.       i  9.  Oculo-motor  nerve. 

5.  Splenium  of  corpus  cal- I  10.  Corpus  mamillare. 

losum.                             I  II.  Infundibulum. 


12.  Optic  chiasma. 

13.  Lamina  terminalis. 

14.  Anterior  commissure. 

15.  Foramen  interventriculare. 

16.  Genu  of  corpus  callosum. 

17.  Septum  pellucidum. 


is  it  touched  by  the  falx  cerebri ;  anteriorly,  that  fold  of  dura 
mater  falls  considerably  short  of  it.  The  upper  surface  of 
the  corpus  callosum  is  coated  by  an  exceedingly  thin  layer 
of  grey  matter  continuous,  at  the  bottom  of  the  callosal 
sulcus,  with  the  grey  cortex  of  the  hemisphere.  In  this  are 
embedded,  on  either  side  of  the  median  plane,  two  delicate 
longitudinal  bands  of  fibres  called  the  striae  longitudinales 
medialis  and  lateralis.  The  stria  loitgitudinalis  medialis  is  the 
more  strongly  marked  of  the  two,  and  it  is  separated  from 
VOL.   II — 31 


482 


THE  BRAIN 


its  fellow  of  the  opposite  side  by  a  faint  median  furrow. 
The  stria  longitudinalis  lateralis  is  placed  more  laterally. 
So  thin  is  the  grey  coating  of  the  corpus  callosum  that 
the  transverse  direction  of  the  bundles  of  callosal  fibres 
can  be  easily  seen  through  it. 

The  striae   with  the   thin  layer  of  grey  matter  associated  with   them 
represent  a  gyrus  called  the  gyrus  stipracallosus. 

The  two  extremities  of  the  corpus  callosum  (Fig.  192)  are 

Genu  of 


Optic  chiasma 
thrown  back 


Lamina  terniinalis 
^^^■sGyrus  subcallosus 


Fig.  193.  —  Anterior  end  of  the  Corpus  Callosum  and  the  Subcallosal  Gyri 
as  seen  from  below  when  the  frontal  lobes  of  the  hemispheres  are 
slightly  separated  from  each  other.      (From  Cruveilhier, ) 

greatly  thickened,  whilst  the  intermediate  part,  the  truncus 
(O.T.  body)  is  considerably  thinner.  The  massive  posterior 
end,  which  is  full  and  rounded,  lies  over  the  mesencephalon, 
and  extends  posteriorly  as  far  as  the  highest  point  of  the  cere- 
bellum. It  is  called  the  splenium.  The  anterior  end,  which 
is  not  quite  so  massive,  is  folded,  downwards  and  posteriorly, 
upon  itself,  and  is  called  the  genu.  The  recurved  lower 
portion  of  the  corpus  callosum  rapidly  thins  as  it  passes 
posteriorly,  and  is  termed  the  rostrum.  The  fine  terminal 
edge  of  the  rostrum,  the  lamina  rostralis,  is  connected  with 
the  lamina  terminalis  (Fig.  192). 

Both  the  lateral  and  the  medial  longitudinal  striae,  which 
lie    upon   the   upper   surface   of   the   corpus   callosum,    turn 


THE  CEREBRUM  483 

downwards,  round  the  splenium,  and  end  in  the  fasciola  ^ 
cinerea.  The  fasciola  cinerea,  which  is  situated  immediately 
beneath  the  splenium,  is  a  narrow  strip  of  grey  matter, 
continuous  posteriorly  with  the  medial  and  lateral  striae 
of  the  same  side  and  anteriorly  with  the  fascia  dentata 
hippocampi.  Anteriorly,  the  striae  pass  round  the  genu,  and 
then  along  the  under  surface  of  the  rostrum  until  they 
terminate  in  the  corresponding  gyrus  subcallosus.  The  gyrus 
subcallosus  is  a  ridge  which  descends  from  the  rostrum  of  the 
corpus  callosum  and  passes  to  the  surface  of  the  substantia 
perforata  anterior.  There  the  fibres  of  the  striae  contained 
in  the  gyrus  emerge  from  its  substance,  and  pass  postero- 
laterally  along  the  posterior  limit  of  the  substantia  perforata 
anterior  towards  the  anterior  extremity  of  the  temporal  lobe. 

Fibres  of  the  Corpus  Callosum. — The  transverse  fibres  of  the  corpus 
callosum,  as  they  enter  the  white  medullary  centre  of  the  cerebral  hemisphere, 
radiate  from  each  other  towards  various  parts  of  the  cerebral  cortex.  This 
radiation  is  called  the  radiatio  corp07'is  callosi.  The  more  anterior  of  the 
fibres  which  compose  the  genu  of  the  corpus  callosum  sweep  anteriorly 
in  a  series  of  curves  towards  the  frontal  pole  of  the  hemisphere.  They 
form  the  forceps  minor.  A  large  part  of  the  splenium,  forming  a  solid 
bundle  termed  the  forceps  major,  bends  suddenly  and  abruptly  posteriorly 
into  the  occipital  lobe.  Fibres  from  the  trunk  of  the  corpus  callosum  and 
also  from  the  splenium  curve  round  the  lateral  ventricle  and  form  a  very 
definite  stratum  called  the  tapetum.  This  is  a  thin  layer  in  the  medullary 
centre  of  the  hemisphere  which  forms  the  roof  and  lateral  wall  of  the 
posterior  horn  and  the  lateral  wall  of  the  posterior  part  of  the  inferior  horn 
of  the  lateral  ventricle. 


Ventriculus  Lateralis. 

The  lateral  ventricle,  in  the  interior  of  the  cerebral  hemi- 
sphere, should  now  be  opened  up  on  each  side.  The  corpus 
callosum,  which  forms  the  roof  of  the  central  part  (O.T.  body) 
and  anterior  horn  of  this  cavity,  must,  therefore,  be  partially 
removed. 

Dissection. — Make  a  longitudinal  incision,  through  the  corpus  callosum, 
about  a  quarter  of  an  inch  from  the  median  plane  on  each  side.  The  central 
portion  of  the  corpus  callosum  which  lies  between  these  incisions  is  to  be 
kept  in  position.  The  lateral  portions  must  be  turned  laterally  and 
detached  completely.  As  this  is  being  done,  it  will  become  evident  that  the 
lower  part  of  the  splenium  which  is  prolonged  into  the  forceps  major  is  in 
reality  a  portion  folded  anteriorly  in  close  apposition  with  the  under  surface 
of  the  posterior  end  of  the  corpus  callosum.  Be  careful  to  leave  the  forceps 
major  in  its  place. 

The  central  part  and  the  anterior  horn  of  the  ventricle  are  now  exposed  ; 
but  the  cavity  of  the  ventricle  runs  posteriorly  into  the  occipital  lobe  in 
11—31  a 


484 


THE  BRAIN 


the  form  of  a  posterior  horn,  and  downwards  and  anteriorly  into  the  temporal 
•lobe  as  the  inferior  horn.  The  posterior  horn  can,  at  present,  be  opened 
on  the  right  side  only.  Carry  the  knife  posteriorly  through  the  medullary 
substance  which  forms  its  roof,  and  remove  a  sufficient  amount  of  this  to 


Genu  of  corpus  callosum 

;  foramen  interventnculare 


Cavum  septi  pellucidi 
Septum  pellucidum  j 


Corpus  callosum 
turned  to  left  side 


Caudate  nucleus 
i  Thalamus 
i  ;       Chorioid  plexus 

'  ;        /         Stria  terminalis 


M  .-/ 

Trigonum  collaterale 

Hippocampus 

Crus  of  fornix 


Calcar  avis 


Forceps  major 

Body  of  fornix 


I      i  Bulb  of  cornu 

I       : 

i   Hippocampus 

Crus  of  fornix 


Pig.  194.— Dissection  to  show  the  Lateral  Ventricles.  The  trunk  of  the 
corpus  callosum  has  been  detached  from  the  genu  and  the  splenmm  and 
turned  over  to  the  left. 

give  a  complete  view  of  the  interior  of  this  part  of  the  cavity.  Greater 
difficulty  will  be  experienced  in  opening  up  the  inferior  horn.  Place  the 
point  of  the  knife  in  the  upper  part  of  the  horn,  where  it  joins  the  central 
part  of  the  ventricle,  and  carry  the  blade  in  an  antero-inferior  direction. 


THE  CEREBRUM 


485 


through  the  lateral  part  of  the  temporal  lobe,  towards  the  temporal  pole, 
following  the  course  of  the  cavity.  This  corresponds  very  nearly  with  the 
course  of  the  superior  temporal  sulcus.  The  lateral  wall  of  the  inferior 
horn  is  thus  incised,  and  a  sufficient  amount  of  the  lateral  part  of  the 
temporal  lobe  must  be  removed  to  give  a  view  of  the  cavity.  In  doing  this, 
the  temporal  operculum  will  be  taken  away,  but  the  surface  of  the  insula 
should  be  preserved  from  injury. 

Lateral  Ventricle. — The  dissector  will  now  perceive  that 
each  cerebral  hemisphere  is  hollow.  The  cavity  in  the  interior 
is  called  the  lateral  ventricle.      It   is  lined  with  a  thin   dark- 


Central  part  of  lateral  ventricle 


Inferior  pineal  rece 
Snperior 
pineal  recess   , 
Aqu£eductu> 
cerebri 


Anterior 
horn  of 
lateral 
ventricle 

Interventricular 

foramen 
Third  ventricle 
ic  recess 


lI^  opti 

Infundibular  recess 


Lateral  recess 


Fig.  195. — Cast  of  the  Ventricles  of  the  Brain  (from  Retzius), 

coloured  layer  of  epithelium,  which  is  termed  the  ependyma.  In 
certain  places  its  walls  are  in  apposition  with  each  other,  but 
in  other  localities  spaces  of  varying  capacity,  and  containing 
cerebro-spinal  fluid,  are  left  between  the  bounding  walls.  The 
lateral  ventricle  communicates  with  the  third  ventricle  of  the 
brain  by  means  of  a  small  foramen,  which  is  termed  the 
interventricular  fora??ien  (O.T.  forame?i  of  Monro).  This 
aperture,  which  is  just  large  enough  to  admit  a  crow-quill, 
lies  at  the  anterior  end  of  the  thalamus,  and  posterior  to 
the  column  of  the  fornix  (O.T.  anterior  pillar). 

The  shape  of  the  lateral  ventricle  is  very  irregular,  and 
can  be  best  understood  by  the  study  of  a  plaster  cast  of 
its  interior  (Fig.  195).  It  is  composed  of  a  central  part 
(O.T.  body)  and  three  horns,  viz.,    an  anterior,  a  posterior, 


486 


THE  BRAIN 


and  an  inferior  horn.     The  anterior  horn  is  that  part  of  the 
cavity   which    Hes  anterior   to    the   interventricular   foramen. 

Caudate  nucleus 


Putamen 


Anterior  commissure 


Pes  hippocampi 
Hippocampus         ,' 
Inferior  cornu  of  '         / 

lateral  ventricle 


^  Genu  of  corpus 
callosum 


Septum 
"5—  ""pellucidum 
-J--.  Cavum  sep.  pell. 

Caudate  nucleus 


_.  Foramen 

interventriculare 


Stria  terminalis 

— s?~-    Thalamus 
"  Fornix 


Medial  longi- 
tudinal striae 


Chorioid  / 
plexus ' 
Fimbria 
Posterior  collateral ,' 
eminence 
Posterior  cornu 

Calcar  avis' 

Forceps  major 

Fig.  196. — Dissection  to  show  the  Posterior  and  Inferior  Cornua  of  the 
Lateral  Ventricle  on  the  left  side. 

The  central  part  is  the  portion  of  the  ventricle  which  extends 
from  the  interventricular  foramen  to  the  splenium  of  the 
corpus  callosum.      At  that  point  the   posterior  and    inferior 


THE  CEREBRUM 


487 


horns  diverge  from  the  posterior  end  of  the  central  part. 
The  posterior  horn  curves  posteriorly  and  medially  into  the 
occipital  lobe.  It  is  very  variable  in  its  length  and  capacity. 
The  inferior  horn  passes  with  a  bold  sweep  round  the 
posterior  end  of  the  thalamus,  and  then  tunnels,  in  an  antero- 
inferior direction,  through  the  temporal  lobe  towards  the 
temporal  pole. 

Corpus  callosum 
Longitudinal  fissure 


Lateral  ventricle 

Chorioid  plexus     | 
Interventricular  forameu 


Claustrum 


Right  column  of  fornix 


1  \  Internal  capsule 

\  ■ 

I  Lentlform  nucleus 

Caudate  nucleus 
Septum  pellucidum 

Fig.  197. — Frontal  section  through  the  Cerebrum  through  the  anterior  part 
of  the  lentiform  nucleus.      Seen  from  the  anterior  aspect. 


Cornu  Anterius  Ventriculi  Lateralis. — The  anterior  horn 
forms  the  anterior  part  of  the  cavity,  and  extends  antero- 
laterally  and  downwards  in  the  frontal  lobe.  When  seen  in 
frontal  section  it  presents  a  triangular  outline — the  floor 
sloping  upwards  and  laterally  to  meet  the  roof  at  an  acute 
angle  (Fig.  197).  It  is  bounded  anteriorly  by  the  posterior 
surface  of  the  genu  of  the  corpus  callosum,  whilst  the  roof  is 
formed  by  the  anterior  part  of  the  trunk  of  the  corpus 
callosum.     The  medial  wall^  which  is  vertical,  is  formed  by 


488 


THE  BRAIN 


the  septum  pellucidum — a  thin  median  partition  between 
the  lateral  ventricles  of  opposite  sides.  The  sloping  floor 
presents  a  marked  elevation  or  bulging,  viz.,  the  smooth 
rounded  and  enlarged  anterior  extremity  of  the  pear-shaped 
caudate  nucleus. 

Pars  Centralis  Ventriculi  Lateralis. — The  central  part 
of  the  ventricle  is  roofed  likewise  by  the  corpus  callosum. 
On  the  medial  side  it  is  bounded  by  the  posterior  part  of  the 
septum  pellucidum,  and  more  posteriorly  by  the  attachment 
of  the    fornix  to  the  under  surface  of  the  corpus  callosum. 

Corpus  callosum     Chorioid  plexus 
Lateral  ventricle       I      I       Striae  on  corpus  callosum 


Caudate  nucleus 
Fronto-occipital  fasciculus 


i    Longitudinal  fissure 
Septum  pellucidum 


Vena  terminalis    i     i 
Subthalamic  body 

Thalamus 


'         I    3rd  ventricle 
Chorioid  plexus 
Red  nucleus 


Fig.  198. — Frontal  Section  showing  immediate  relations  of  Lateral  and 
Third  Ventricles.     (Part  of  Fig.  217  enlarged.) 

On  the  lateral  side  it  is  closed,  as  in  the  case  of  the  anterior 
horn,  by  the  meeting  of  the  roof  and  the  floor  of  the  cavity. 

On  the  floor  a  number  of  important  objects  may  be 
recognised.  Latero-medially,  and,  at  the  same  time,  to  some 
extent  antero-posteriorly,  these  are — ( i )  the  caudate  nucleus  ; 

(2)  a  groove  extending  obliquely,  postero-laterally,  between 
the  caudate  nucleus  and  the  thalamus,  in  which  are  placed 
the  terminal  vein  (O.T.  vein  of  corpus  striatum)  and  a  white 
band  called  the  stria  terminalis  (O.T.  taenia  semicircularis) ; 

(3)  a  portion  of  the  upper  surface  of  the  thalamus ;  (4) 
the  chorioid  plexus  j  (5)  the  thin  sharp  lateral  edge  of  the 
fornix. 


THE  CEREBRUM 


489 


The  caudate  nucleus  as  it  passes  posteriorly,  on  the  lateral 
part  of  the  floor  of  the  central  part  of  the  lateral  ventricle, 
narrows  very  rapidly. 

The  terminal  vein  is  seen  through  the  ependyma  in  the 
groove  between  the  caudate  nucleus  and  the  thalamus.  It 
joins  the  internal  cerebral  vein  (O.T.  vein  of  Galen)  at  the 
interventricular  foramen.  In  the  same  groove  is  placed  the 
stria  terminalis — a  narrow  band  of  white  matter,  which  bends 
downwards  and  disappears    from  view   in  the  region  of  the 


Eulb  of  cornu 


Splenium 


Bulb  of  cornu 


\    \  Calcar  avis 
\  Tapetum 

\  Optic  radiation 
Inferior  longitudinal  bundle 

Fig.  199. — Frontal  section  through  the  Posterior  Horns  of  the 
Lateral  Ventricles. 

interventricular    foramen.       Its     fibres    ultimately    reach    the 
substantia  perforata  anterior,  in  which  they  end. 

The  portion  of  the  upper  surface  of  the  thala?nus^  which 
appears  in  the  floor  of  the  lateral  ventricle  is,  in  great  part, 
covered  by  the  chorioid  plexus  of  the  lateral  ventricle.  The 
plexus  is  a  rich  vascular  fringe  which  appears  from  under 
cover  of  the  sharp  lateral  edge  of  the  fornix.  It  is  con- 
'tinuous  anteriorly,  through  the  interventricular  foramen,  with 
the  corresponding  chorioid  plexus  of  the  opposite  side ;  whilst 
posteriorly,  it  is  carried  into  the  inferior  horn  of  the  ventricle. 
Although  the  chorioid  plexus  has  all  the  appearance  of  lying 
free  within  the  ventricle  it  is  invested  by  an  epithelial  layer 


490  THE  BRAIN 

of  ependyma,  which  excludes  it  from  the  cavity  and  is 
connected  on  the  one  hand  to  the  sharp  margin  of  the  fornix, 
and  on  the  other  to  the  upper  surface  of  the  thalamus. 

Cornu  Posterius  Ventriculi  Lateralis.  —  The  posterior 
horn  is  a  diverticulum  which  runs,  from  the  posterior  end  of  the 
central  part  of  the  ventricle,  into  the  occipital  lobe.  It  tapers 
to  a  point  and  describes  a  gentle  curve,  the  convexity  of 
which  is  directed  laterally.  The  roof  and  lateral  wall  of 
this  portion  of  the  ventricular  cavity  is  formed  by  the  tapetum 
of  the  corpus  callosum. 

Upon  the  medial  wall  two  elongated  curved  elevations 
may  be  seen.  The  upper  of  these,  termed  the  bulb  of  the 
cornu,  is  produced  by  the  fibres  of  the  forceps  major  as 
they  curve  posteriorly,  from  the  lower  part  of  the  splenium 
of  the  corpus  callosum,  into  the  occipital  lobe.  The  lower 
elevation  is  known  as  the  calcar  avis.  It  varies  greatly  in 
size,  in  different  brains,  and  is  caused  by  an  infolding  of  the 
ventricular  wall  which  corresponds  with  the  anterior  part  of 
the  calcarine  fissure. 

Dissection.  —  The  dissector  should  now  insinuate  his  fingers  underneath 
the  fronto-parietal  operculum  of  the  insula  and  tear  this  portion  of  the 
cortex  away  in  an  upward  direction.  The  frontal  operculum  (pars 
triangularis)  and  the  orbital  operculum  should  be  dealt  with  in  the  same 
manner.  The  greater  part  of  the  temporal  operculum  has  already  been 
removed  in  opening  up  the  inferior  horn  of  the  ventricle  ;  therefore  the 
insula  is  now  fully  exposed  to  view,  and  its  relation  to  the  parts  in  the 
interior  of  the  ventricle  can  be  seen. 

Cornu  Inferius  Ventriculi  Lateralis  (O.T.  Descending 
Cornu). — The  inferior  horn  must  be  regarded  as  the  direct 
continuation  of  the  main  ventricular  cavity  into  the  temporal 
lobe.  The  posterior  horn  is  merely  a  diverticulum  from  the 
main  cavity.  At  first  directed  postero-laterally,  the  inferior 
horn  suddenly  sinks  downwards,  posterior  to  the  thalamus,  into 
the  temporal  lobe,  in  which  it  takes  a  curved  course,  antero- 
medially,  to  a  point  about  an  inch  posterior  to  the  extremity 
of  the  temporal  pole.  In  the  angle  between  the  diverging 
inferior  and  posterior  horns  the  cavity  of  the  ventricle  exhibits 
a  triangular  expansion  of  varying  capacity.  This  is  called  the 
tngonum  collaterale. 

The  lateral  wall  of  the  inferior  horn  is  formed,  for  the 
most  part,  by  the  tapetum  of  the  corpus  callosum.  At  the 
extremity  of  the  horn  the  roof  presents  a  slight  bulging  into  the 
ventricular  cavity.     This  is  the  amygdaloid  tubercle,  and  it  is 


THE  CEREBRUM 


491 


produced  by  a  superjacent  collection  of  grey  matter,  termed 
the  amygdaloid  nucleus.  The  stria  termifialis  and  the  greatly 
attenuated  and  expanded  tail  of  the  caudate  nucleus  are  both 
prolonged  into  the  inferior  horn,  and  are  carried  anteriorly  in 
its  roof  to  the  amygdaloid  nucleus. 

On  the  floor  of  the  inferior  horn  the  dissector  will  note 
the  following  parts:  (i)  the  hippocampus;  (2)  the  chorioid 
plexus;  (3)  the  fimbria;  and  (4)  the  eminentia  collateralis. 

Hippocampus  (O.T.  Hippocampus  Major). — This  is  over- 
lapped by  the  chorioid  plexus,  which  must  be  turned  aside. 


optic  tract 
Stria  terminalis     |    Fimbria 
Chorioid  plexus 
Caudate  nucleus  ', 
Inferior  cornu  of  lateral  ventricle 


Subthalamic  body 
!   Basis  pedunculi 
Red  nucleus 


Fig. 


Collateral  eminence         I  '      Pia-mater 

Collateral  fissure     Cerebellum 

200. — Frontal  Section  to  show  relations  of  Inferior  Cornu  of 
Lateral  Ventricle.      (Part  of  Fig.  217  enlarged.) 


It  is  a  prominent  elevation  on  the  floor  of  the  inferior  horn 
of  the  lateral  ventricle,  and  is  strongly  curved  in  conformity 
with  the  course  taken  by  the  horn  in  which  it  lies.  It  pre- 
sents, therefore,  a  medial  concave  margin  and  a  lateral  convex 
margin.  Narrow  posteriorly,  it  enlarges  as  it  is  traced 
anteriorly,  and  it  ends,  below  the  amygdaloid  tubercle,  in  a 
thickened  extremity,  the  pes  hippocampi.  The  surface  of  the 
pes  hippocampi  is  marked  by  some  faint  grooves  which  inter- 
vene between  a  number  of  ridges  called  the  hippocampal 
digitations.  The  hippocampus  is  the  internal  elevation  which 
corresponds  to  the  hippocampal  fissure  on  the  exterior  of  the 
wall  of  the  ventricle. 

Fimbria  (Hippocampi). — The  fimbria  is  a  narrow  but  very 


492 


THE  BRAIN 


distinct  band  of  white  matter  which  is  attached  by  its  lateral 
margin  along  the  concave  medial  border  of  the  hippocampus. 
The  white  matter  composing  it  is  continuous  with  the  thin 
white  layer  (alveus)  which  is  spread  over  the  surface  of  the 
hippocampus,  and  it  presents  two  free  surfaces  and  a  sharp 
free  medial  border.  The  fimbria  has  been  noted  already 
in  connection  with  the  hippocampal  fissure  and  the  fascia 
dentata  (p.  479),  and  the  relations  which  it  presents  to  the 
crus  of  the  fornix  and  the  uncus  are  pointed  out  on  p.  494. 

Pes  hippocampi 
Hippocampus 
Anterior  collateral  eminence 


Uncus -^ 

Frenulum  Giacomini  - 

Fimbria *- 

Fascia  dentata 4 _ 

Fornix  ---      \    ,-- 

Hippocampal 
gyrus 
Splenium   ;^r 


Trigonum  collaterale 

Calcar  avis 


Posterior  horn 


Bulb  of  cornu 


Fjg.  20I. — Dissection  to  show  the  Posterior  and  Inferior  Cornua  of  the 

Lateral  Ventricle. 

Chorioid  Fissure  of  the  Cerebrum. — When  the  pia  mater 
in  the  region  of  the  hippocampal  fissure  is  removed  from  the 
surface  of  the  brain,  the  chorioid  plexus  in  the  interior  of  the 
inferior  horn  of  the  lateral  ventricle  is  usually  withdrawn  with 
it,  and  a  fissure  appears  between  the  fimbria  and  the  roof 
of  the  ventricular  horn.  This  is  termed  the  chorioid  fissure  of 
the  cerebrum  ;  it  is  the  lower  part  of  the  great  transverse  fissure. 
By  the  withdrawal  of  the  chorioid  plexus  it  is  converted  into 
an  artificial  gap,  which  leads  directly  from  the  exterior  of  the 
brain  into  the  interior  of  the  inferior  horn  of  the  lateral 
ventricle. 


THE  CEREBRUM 


493 


Plexus  Chorioideus. — The  chorioid  plexus  is  a  system  of 
convoluted  blood-vessels  enclosed  within  a  fold  of  pia 
mater    which    is    prolonged,   into    the    inferior    horn    of   the 


Body  of  lateral  ventricle 
Grey  matter  of 
aqueduct 
Aquaeductus 
cerebri 


Chorioid  plexus 
I         Caudate  nucleus 

Optic  radiation 
I         Caudate  nucleus  (tail) 


^  Optic  radiation 

Inferior  longitudinal  bi 
Tapetum 
Chorioid  plexus 

Infeiior  horn  of  lateral  ventricle 
Alveus 


Lateral  lemniscus 


Medial  geniculate  body 

Hippocampal  gyru 


Hippocampus 
Fimbria 

Fascia  dentata 

Lateral  geniculate  body 

Chorioid  fissure 


Fig.  202. — Frontal  section  through  the  Cerebrum,  Mid-brain,  and  Pons  in  the 
plane  of  the  geniculate  bodies.  It  shows  the  relation  of  the  dentate  and 
chorioid  fissures  to  the  inferior  horn  of  the  lateral  ventricle. 

lateral  ventricle,  through  the  chorioid  fissure  of  the  cerebrum. 
It  lies  on  the  surface  of  the  hippocampus  and,  at  the 
posterior  extremity  of  the  thalamus,  it  becomes  continu- 
ous with    the   chorioid    plexus   in    the    central    part    of   the 


494  THE  BRAIN 

lateral  ventricle  (Fig.  200).  But  it  must  not  be  supposed 
that  the  chorioid  plexus  lies  free  in  the  ventricular  cavity.  It 
is  clothed  in  the  most  intimate  manner  by  an  epithelial  epen- 
dymal  layer,  which  represents  the  medial  wall  of  the  inferior 
horn  pushed  into  the  cavity  by  the  chorioid  plexus.  The 
ventricle,  therefore,  opens  on  the  surface  through  the  chorioid 
fissure  only  after  this  thin  epithelial  layer  is  torn  away  by 
the  withdrawal  of  the  chorioid  plexus. 

Eminentia  Collateralis. — This  eminence  may  present  two 
distinct  forms,  which  may  be  distinguished  from  each  other 
as  the  eminentia  collateralis  posterior  and  the  eminentia  col- 
lateralis anterior. 

T)\t  posterior  collateral  eminence  is  a  smooth  elevation  in 
the  floor  of  the  trigonum  collaterale,  in  the  interval  between 
the  calcar  avis  and  the  hippocampus  as  they  diverge  from 
each  other.  The  anterior  collateral  eminence  is  not  always 
present.  It  forms  an  elongated  elevation  on  the  floor  of  the 
inferior  horn  of  the  lateral  ventricle,  on  the  lateral  side  of 
the  hippocampus.  Both  eminences  correspond  to  the  col- 
lateral fissure  on  the  tentorial  aspect  of  the  cerebral 
hemisphere. 

Dissection. — The  remains  of  the  right  temporal  lobe  and  of  the  right 
occipital  lobe  should  now  be  detached  from  the  cerebrum  by  cutting  through 
the  forceps  major  of  the  splenium  of  the  corpus  callosum  and  through 
the  fimbria  where  it  passes  into  the  crus  of  the  fornix.  The  knife  should 
then  be  carried  anteriorly  from  the  anterior  extremity  of  the  inferior 
horn,  above  the  level  of  the  uncus,  through  the  temporal  pole.  The 
temporal  lobe,  with  the  hippocampal  gyrus  along  its  medial  side,  can 
then  be  separated  from  the  remainder  of  the  brain,  along  the  line  of 
the  chorioid  fissure  of  the  cerebrum.  In  the  detached  part  of  the  cerebrum 
(Fig.  201)  a  good  view  is  obtained  of  the  floor  of  the  inferior  horn  and 
of  the  parts  in  relation  to  it.  Further,  by  replacing  it  in  position,  the 
chorioid  fissure  can  be  better  understood,  and  by  turning  the  brain  upside 
down  a  view  is  obtained  of  the  roof  of  the  inferior  horn  and  the  structures 
in  relation  to  it.  In  this  way  the  tail  of  the  caudate  nucleus  and  the  stria 
terminalis  can  be  traced  into  the  amygdaloid  nucleus. 

The  cut  edge  of  the  central  part  of  the  corpus  callosum,  which  is  still  in 
position,  should  now  be  still  further  pared  away,  so  as  to  bring  the  sub- 
jacent septum  pellucidum  and  the  fornix  more  fully  into  view. 

Fimbria  (Figs.  200,  201). — This  is  simply  a  continuation 
of  the  crus  (O.T.  posterior  pillar)  of  the  fornix.  It  is  a  con- 
spicuous band  of  white  matter,  which  presents  a  prominent  free 
border.  Anteriorly,  it  runs  into  the  recurved  extremity  of 
the  uncus,  whilst,  if  it  is  traced  posteriorly,  it  will  be  seen 
to   curve  upwards,    posterior  to   the   thalamus,   and  become 


THE  CEREBRUM  495 

continuous  with  the  crus  of  the  fornix  below  the  posterior 
part  of  the  corpus  callosum  (p.  491). 

Fascia  Dentata  Hippocampi.  —  The  fascia  dentata  is 
the  free  edge  of  grey  matter  which  is  placed  between  the 
fimbria  and  the  deep  part  of  the  upper  surface  of  the  hippo- 
campal  gyrus.  The  groove  between  it  and  the  fimbria 
is  termed  the  fimbrio-dentate  sulcus.  Its  margin  is  notched, 
and  its  surface  is  scored  with  numerous  closely-placed 
transverse  grooves.  It  begins  posteriorly,  in  the  region  of 
the  splenium  of  the  corpus  callosum,  and  it  runs  anteriorly 
into  the  cleft  of  the  uncus,  from  which  it  emerges  again  in 
the  form  of  a  delicate  band,  called  the  frenulum  of  Giacomini, 
which  crosses  the  recurved  part  of  the  uncus  in  a  transverse 
direction. 

Hippocampal  Fissure. — This  is  a  complete  fissure,  and  the 
elevation  on  the  ventricular  wall,  which  corresponds  to  it,  is 
called  the  hippocampus  (Fig.  217).  It  begins  posterior  to 
the  splenium  of  the  corpus  callosum,  where  it  is  continuous 
with  a  shallow  part  of  the  callosal  sulcus,  and  it  passes 
anteriorly,  between  the  fascia  dentata  and  the  hippocampal 
gyrus.     Its  anterior  end  is  embraced  by  the  uncus. 

Septum  Pellucidum — Fornix — Tela  Chorioidea 
Ventriculi  Tertii. 

Septum  Pellucidum. — This  is  a  thin  vertical  partition  which 
intervenes  between  the  anterior  cornua  and  the  anterior  parts 
of  the  central  portions  of  the  two  lateral  ventricles  (Fig.  198). 
It  is  triangular  in  shape,  and  is  prolonged  posteriorly  in  the 
narrow  interval  between  the  trunk  of  the  corpus  callosum 
and  the  fornix,  to  each  of  which  it  is  attached.  Anteriorly, 
it  occupies  the  gap  posterior  to  the  genu  of  the  corpus 
callosum ;  whilst  below,  in  the  narrow  interval  between  the 
rostrum  of  the  corpus  callosum  and  the  fornix,  it  is  prolonged 
downw^ards  to  the  base  of  the  brain  (Fig.  207). 

The  septum  pellucidum  is  composed  of  tw^o  thin  lamince 
which  lie  one  on  each  side  of  the  median  plane.  The  median 
cleft  between  the  layers  is  termed  the  cavum  septi  pellucidi 
{O.T.  fifth  ventricle)  (Figs.  194  and  196). 

Dissection. — The  narrow  middle  strip  of  the  corpus  callosum,  posterior 
to  the  gemi,  should  now  be  removed.  Cut  it  transversely  across,  and,  gently 
raising  it,  separate  the  upper  edge  of  the  septum  pellucidum  from  its  lower 


496 


THE  BRAIN 


surface.  Posterior  to  the  septum  pellucidum  the  under  surface  of  the 
median  part  of  the  corpus  callosuni  will  be  found  to  lie  upon  and  to  be 
connected  with  the  upper  surface  of  the  fornix.  Sever  this  connection 
also.  The  left  half  of  the  forceps  major  should  be  preserved,  so  that  its 
connection  with  the  occipital  lobe  may  be  more  fully  made  out  later.  By 
snipping  off  the  upper  edge  of  the  septum  pellucidum  with  the  scissors,  the 
two  laminae,  with  the  interposed  cleft,  will  be  exposed. 

Cavum  Septi  Pellucidi  (O.T.  Fifth  Ventricle).— This  is  the 
name  which  is  applied  to  the  median  cleft  between  the  two 
laminae  of  the  septum  pellucidum.  It  varies  greatly  in  extent, 
in  different  brains,  and  it  contains  a  little  fluid.    It  is  completely 

Fasciculus  thalamo-mamillaris 


Taenia  thalami 
Base  of  pineal  body 


Corpus  callosum 
Rostrum 


Sulcus  for  falx 
cerebri 

Splenium 

Median  part  of 

transverse  fissure 

Fasciola  cinerea 

Isthmus 


Genu 


-  Column  of  fornix 
Anterior  commissure 
Subcallosal  gyrus 


Upper  quadrigeminate  body 

Posterior  commissure       "j 
Fimbria 


'         *^  Optic  recess 
L     Optic  chiasma 
Uncus 
Mamillary  body 


Fig,  203. — Dissection  showing  the  relations  of  the  Fornix. 

isolated,  having  no  communication  either  with  the  ventricles 
or  with  the  exterior. 

Fornix. — The  fornix  is  an  arched  structure,  composed  of 
longitudinal  and  transverse  fibres.  It  consists  of  a  central 
part  or  body,  which  ends  in  two  columns  anteriorly  and  two 
crura  posteriorly. 

Corpus  Fornicis. — The  body  of  the  fornix  is  triangular  in 
shape.  Anteriorly,  where  it  is  continuous  with  the  columns, 
it  is  narrow ;  posteriorly  it  broadens  out,  becomes  flattened, 
and  is  prolonged  into  the  crura.  The  upper  surface  of  the 
body  of  the  fornix  is  in  contact  with  the  under  surface  of  the 
corpus  callosum,  and  is  adherent  to  it  in  the  median  plane 


THE  CEREBRUM  497 

posteriorly.  More  anteriorly  it  is  attached  to  the  posterior 
part  of  the  lower  edge  of  the  septum  pellucidum.  Beyond 
these  attachments  the  upper  surface  of  the  body  of  the  fornix 
forms  a  part  of  the  floor  of  the  lateral  ventricle,  on  each  side, 
and  is  clothed  with  ependyma.  It  presents  a  sharp  lateral 
edge,  from  under  which  the  chorioid  plexus  projects  into  the 
cavity  of  the  lateral  ventricle.  The  lower  surface  of  the 
body  of  the  fornix  rests  upon  the  tela  chorioidea  of  the  third 
ventricle  (O.T.  velum  interpositum),  a  fold  of  pia  mater  which 
separates  it  from  the  third  ventricle  and  the  two  thalami. 

Columnce  Fornicis  (O.T.  anterior  pillars). — The  two  columns 
of  the  fornix  are  two  rounded  strands  which  emerge  from  the 
anterior  end  of  the  body  of  the  fornix,  and  then,  diverging 
slightly,  pass  downwards  anterior  to  the  interventricular 
foramen.  Their  lower  ends  sink  into  the  grey  matter  on  the 
lateral  walls  of  the  third  ventricle,  and  end  at  the  base  of  the 
brain  in  the  corpora  mamillaria. 

Each  corpus  mamillare  has  the  appearance  of  being  a  twisted  loop  of 
the  corresponding  column  of  the  fornix,  in  which  the  fibres  turn  upon 
themselves,  and  are  then  continued  upwards  and  posteriorly  into  the 
anterior  tubercle  of  the  thalamus.  This  appearance,  however,  is  decep- 
tive. In  the  interior  of  the  corpus  mamillare  there  is  a  nucleus  of  grey 
matter.  In  this  the  fibres  of  the  column  end  ;  while  the  other  fibres, 
which  seem  to  be  continuous  with  the  fornix  fibres,  take  origin  within  the 
nucleus.  The  strand,  thus  formed,  is  called  the  fasciculus  thalamo- 
mamillaris  (O.T.  bundle  of  Vicq  d'Azyr)  (Fig.  203). 

The  connections  which  have  just  been  described  cannot  be  made  out  at 
present,  but  at  a  later  period  the  dissector  will  experience  little  difficulty 
in  tracing  the  column  of  the  fornix  to  the  corpus  mamillare,  and  in  dis- 
playing the  connection  of  this  with  the  fasciculus  thalamo-mamillaris. 

Crura  Fornicis  (O.T.  posterior  pillars). — The  crura  of  the 
fornix  are  flattened  bands  which  diverge  widely  from  the  body 
of  the  fornix.  At  first  they  are  adherent  to  the  under  sur- 
face of  the  corpus  callosum,  but  soon  they  sweep  downwards, 
round  the  posterior  ends  of  the  thalami,  and  enter  the  inferior 
horns  of  the  lateral  ventricles.  There  each  crus  comes  into 
relation  with  the  corresponding  hippocampus,  and  a  portion  of 
its  fibres  become  spread  out  on  the  surface  of  that  prominence, 
forming  the  alveus,  whilst  the  remainder  constitute  the  fimbria, 
which  has  been  described  already  (p.  494,  Fig.  203). 

The  transverse  fibres  of  the  fornix  cross  the  lower  surface 
of  the  body  and  the  anterior  part  of  the  interval  between  the 
diverging  crura.  In  the  latter  place  they  may  be  adherent 
to  the  lower  surface  of  the  corpus  callosum.      On  each  side 

VOL.  II — 32 


498 


THE  BRAIN 


they  are  continuous  with  the  longitudinal  fibres  of  the  crura 
and  constitute  a  transverse  commissure  between  the  hippo- 
campi of  opposite  sides. 

Dissection. — The  body  of  the  fornix  should  now  be  divided  transversely, 
across  its  middle.  Its  posterior  and  anterior  portions  may  then  be  raised 
from  the  tela  chorioidea  of  the  third  ventricle,  and  thrown  apart  from 
each  other.  Had  it  been  possible  to  raise  the  corpus  callosum  and  fornix 
together,  the  diverging  crura  of  the  fornix  would  have  been  seen  to  limit 


Cavum  septi  pellucldi 


Genu  of  corpus  callosum 


■\ 


Fornix  divided 


Vena 
terminalis  ""--.  / 


Stria 
terminalis   "•■ 


Internal  cerebral  vein"' 


Crus  of  fornix 


:  \.-   Septum  pellucidum 
X-^V--  Caudate  nucleus 


Column 
,--  of  fornix 


Tela  chorioidea 
of  third  ventricle 


Chorioid  plexus 


Body  of  fornix 
reversed 


Fig.  204. — Dissection  to  show  the  Tela  Chorioidea  of  the  Third  Ventricle  and 
the  parts  in  its  vicinity.      The  fornix  has  been  divided  and  thrown  posteriorly. 


a  triangular  space  on  the  under  surface  of  the  corpus  callosum,  anterior  to 
the  posterior  margin  of  the  splenium.  This  interval  is  termed  the  lyra  ; 
it  is  traversed  by  a  series  of  oblique  markings  which  indicate  the  presence 
of  the  transverse  fibres  passing  across  from  one  crus  of  the  fornix  to  the 
other. 

Tela  Chorioidea  Ventriculi  Tertii  (O.T.  Velum  Inter- 
positum). — This  lamina  is  formed  by  a  double  layer  of  pia 
mater  which  intervenes  between  the  body  of  the  fornix  above, 
and  the  roof  of  the  third  ventricle  and  the  two  thalami  below. 
Between  the  two  layers  are  blood-vessels  and  some  subarach- 


THE  CEREBRUM  499 

noidal  trabecular  tissue.  In  shape  this  tela  is  triangular,  and 
the  narrow  anterior  end  or  apex  reaches  the  interventricular 
foramen.  The  base  lies  under  the  splenium  of  the  corpus 
callosum,  and  there  the  two  layers  of  pia  mater  which  form 
the  tela  become  continuous  with  the  pia  mater  on  the  surface 
of  the  brain. 

Along  each  lateral  margin  the  tela  is  bordered  by  the 
chorioid  plexus  of  the  central  part  of  the  lateral  ventricle, 
which  projects  into  the  ventricular  cavity  from  under  cover 
of  the  lateral  free  edge  of  the  fornix.  Posteriorly,  this 
chorioid  plexus  is  continuous  with  the  plexus  in  the  inferior 
horn  of  the  ventricle ;  whilst  anteriorly,  it  narrows  greatly, 
and  becomes  continuous,  across  the  median  plane,  with  the 
corresponding  plexus  of  the  opposite  side.  From  this 
median  junction  two  much  smaller  chorioid  plexuses  run 
posteriorly,  on  the  under  surface  of  the  tela,  and  project 
downwards  into  the  third  ventricle.  These  are  the  chorioid 
plexuses  of  the  third  ventricle  (Fig.  205). 

The  most  conspicuous  blood-vessels  in  the  tela  chorioidea 
of  the  third  ventricle  are  the  two  vence  cerebri  internee. 
(O.T.  veins  of  Galen),  which  run  posteriorly — one  on  either 
side  of  the  median  plane.  Anteriorly,  each  is  formed,  at  the 
apex  of  the  fold,  by  the  union  of  the  vena  terminalis  with  a 
large  vein  issuing  from  the  chorioid  plexus ;  posteriorly,  they 
unite  to  form  the  great  cerebral  vein  (O.T.  vena  magna 
Galeni),  and  this  pours  its  blood  into  the  anterior  end  of 
the  straight  sinus  (Fig.  88). 

Transverse  Fissure. — This  name  is  given  to  the  continuous 
cleft  through  which  the  tela  chorioidea  of  the  third  ventricle 
and  the  chorioid  plexuses  of  the  two  inferior  horns  of  the 
lateral  ventricles  are  introduced  into  the  interior  of  the  brain. 
It  consists  of  an  upper  or  intermediate  part  and  two  lateral 
parts.  The  intermediate  part  passes  anteriorly  between  the 
splenium  of  the  corpus  callosum  and  the  body  of  the  fornix 
above,  and  the  roof  of  the  third  ventricle  and  the  thalami 
below.  It  is  limited  by  the  ependymal  covering  of  the 
chorioid  plexuses,  which  shuts  out  these  structures  from  the 
cavity  of  the  lateral  ventricles. 

The  lateral  parts  of  the  transverse  fissure  are  the  chorioidal 
fissures.     Each  is  continuous  with  the  intermediate  part,  and 
has    been   studied    already  in    connection   with    the    inferior 
horn  of  the  lateral  ventricle  (p.  492). 
II— 32  a 


500 


THE  BRAIN 


Dissection. — Each  vena  terminalis  should  now  be  divided  as  it  unites 
with  the  internal  cerebral  vein.  The  apex  of  the  tela  chorioidea  should 
then  be  seized  with  the  forceps  and  pulled  posteriorly,  till  the  whole 
structure  is  reversed.  The  entire  upper  surface  of  the  thalamus  on 
each  side  is  thus  exposed,  and,  between  the  thalami,  is  seen  the  third 
ventricle.  The  epithelial  roof  of  this  ventricle,  which  is  invaginated  into 
the  cavity  by  the  chorioid  plexuses  of  the  third  ventricle  on  the  under 
surface  of  the  tela,  is  torn  away  with  the  tela.  The  basal  part  of  the  tela 
is  intimately  connected  with  the  pineal  body,  which  lies  on  the  mesen- 
cephalon behind  the  third  ventricle.  Care  therefore  must  be  taken  to 
extricate  this  body  from  the  pia  mater  ;  otherwise  it  is  sure  to  be  pulled 
away. 


The  Thalami  and  the  Third  Ventricle. 

Thalamus. — The  thalamus  is  a  large  mass  of  grey  matter 
which  lies  obliquely  across  the  path  of  the  pedun cuius  cerebri 
as  it  ascends  into  the  hemisphere.      The  smaller  anterior  end 

Corpus  callosuni     Chorioid  plexus 
Lateral  ventricle      '      I.      Striae  on  corpus  callosum 


Caudate  nucleus 
Fronto-occipital  fasciculus 


■^  Longitudinal  fissure 
Septum  pellucidum 


Vena  terminalis 
Subthalamic  body 

Thalamus 


I        I   3rd  ventricle 
Chorioid  plexus 
Red  nucleus 


Fig.  205. — Frontal  section  showing  immediate  relations  of  Lateral  and 
Third  Ventricles.      (Part  of  Fig.  217  enlarged. ) 


of  the  thalamus  lies  close  to  the  median  plane,  and  is  separ- 
ated from  the  corresponding  part  of  the  opposite  side  only 
by  a  very  narrow  interval.  The  enlarged  posterior  ends  of 
the  two  thalami  are  placed  more  widely  apart ;  and  in  the 
interval  between  them,  the  corpora  quadrigemina  are  situated. 
In  their  anterior  two-thirds,  the  two  thalami  lie  close  together, 
but  are  separated  by  a  deep  median  cleft,  the  third  ventricle 


THE  CEREBRUM 


501 


of  the  brain.  Each  thalamus  presents  an  anterior  and  a 
posterior  extremity,  and  four  surfaces.  The  inferior  and 
lateral  surfaces  are  in  apposition  and,  indeed,  directly  con- 
nected with  adjacent  parts.  The  superior  and  medial  surfaces 
are  free. 

The  lateral  surface  of  the  thalamus  is  applied  to  a  mass 


Cut  surface  of  genu 
of  corpus  call'j>uin 


Genu  of  corpus  callosum 


Cavum  septi  pellucidi --- 


Fornix 

Anterior  commissure 

IMassa  intermedia 


Groove  on  thalamus  __- 
for  fornix 


Posterior  commissure  .-'' 
Trochlear  nerve  ' 
Brachium  pontis  ' 
Corpora  quadrigemina 


-  Septum  pellucidum 
3P  -  Caudate  nucleus 


Right  column  of  fornix 

Anterior  tubercle  of 
thalamus 


" "  Vena  terminalis 
"""  Ventricle  iii. 
""     Taenia  thalami 

^  Trigonum  habenulae 

'Pulvinar 

Stalk  of  pineal  body 
Pineal  body 


Brachium  conjunctlvum 


Lingula  of  cerebellum 
Medulla  oblongata 


Fig.  206. — The  two  Thalami  and  the  Third  Ventricle 
as  seen  from  above. 

of  white  matter,  termed  the  internal  capsule^  which  is  composed 
largely  of  fibres  from  the  basis  pedunciili.  The  inferior  or 
ventral  surface  of  the  thalamus  rests  chiefly  upon  the  sub- 
thalamic regio?i,  which  is  the  prolongation  upwards  of  the 
tegmental  part  of  the  pedunculus  cerebri.  The  relation, 
therefore,  which  the  thalamus  presents  to  the  upward  continua- 
tion of  the  pedunculus  cerebri  is  very  intimate. 

The  superior  surface  of  the  thalamus  is  free.  On  the 
lateral    side    it     is    bounded     by    the    groove    which     inter- 

II— 32  J 


502-  THE  BRAIN 

venes  between  the  thalamus  and  the  caudate  nucleus  and 
contains  the  vena  terminalis  and  the  stria  terminalis.  On 
the  medial  side,  the  superior  surface  of  the  thalamus  is 
separated,  in  its  anterior  half,  from  the  medial  surface  by  a 
sharp  edge,  or  prominent  ledge,  of  the  ependyma  of  the 
third  ventricle.  This  is  called  the  tcenia  thalamic  and  the 
ridge  which  it  forms  is  accentuated  by  the  fact  that  subjacent 
to  it  there  lies  a  longitudinal  strand  of  fibres  called  the  stria 
medullaris.  A  short  distance  anterior  to  the  pineal  body  the 
taenia  lies  upon  the  upper  border  of  a  raised  white  band,  the 
habenula. 

The  habenula  divides  posteriorly  into  two  parts,  one  of  which  becomes 
continuous  with  the  pineal  body,  whilst  the  other  passes  across  to  the 
opposite  habenula,  through  the  habenular  commissure,  which  lies  anterior 
to  the  pineal  stalk. 

Between  the  habenula  medially  and  the  upper  quadrigeminal 
body  posteriorly,  lies  a  small  triangular  depressed  area,  the 
trigonum  habenulce. 

The  superior  surface  of  the  thalamus  is  slightly  convex, 
and  is  of  a  whitish  colour  owing  to  the  presence  of  a  thin 
superficial  coating  of  nerve  fibres  (stratum  zonale).  It  is 
divided  into  two  areas  by  a  faint  oblique  groove  which 
begins  near  the  anterior  extremity  of  the  thalamus,  and  ex- 
tends obliquely,  laterally  and  posteriorly.  This  sulcus  corre- 
sponds to  the  free  lateral  edge  of  the  fornix.  The  two  areas 
thus  mapped  out  are  very  differently  related  to  the  ventricles 
of  the  brain.  The  lateral  area  includes  the  anterior  extremity 
of  the  thalamus,  and  forms  a  part  of  the  floor  of  the  lateral 
ventricle ;  it  is  covered  with  ependyma,  and  overlapped  by 
the  chorioid  plexus.  The  medial  area  intervenes  between 
the  lateral  and  third  ventricles  of  the  brain,  and  takes  no 
part  in  the  formation  of  the  walls  of  either.  It  is  covered 
with  the  tela  chorioidea,  above  which  is  the  fornix.  It 
includes  the  posterior  extremity  of  the  thalamus. 

The  anterior  extremity  of  the  thalamus,  called  the  anterior 
tubercle,  is  rounded  and  prominent.  It  projects  into  the 
lateral  ventricle,  lies  postero-lateral  to  the  free  portion  of  the 
column  of  the  fornix,  and  bounds  the  interventricular  foramen 
posteriorly. 

The  posterior  extremity  of  the  thalamus  is  very  prominent, 
and  projects  posteriorly  over  the  mesencephalon  (Fig.  206). 
This  projecting  part  is  called  the  pulvinar.     But  the  posterior 


THE  CEREBRUM  503 

end  of  the  thalamus  shows  another  prominence.  This  is 
situated  below  and  to  the  lateral  side  of  the  pulvinar.  It  is 
oval  in  form,  and  receives  the  name  of  the  corpus  geniculattwi 
laterale. 

The  medial  surfaces  of  the  two  thalami  are  placed  very 
close  together,  and  are  covered  not  only  with  the  lining 
ependyma  of  the  third  ventricle,  but  also  with  a  moderately 
thick  layer  of  grey  matter  continuous  with  the  grey  matter 
which  surrounds  the  aquceductus  cerebri  (Sylvius).  A  band 
of  grey  matter,  termed  the  massa  intermedia,  crosses  the  third 
ventricle  and  joins  the  two  thalami  together. 

Corpus  Pineale. — This  is  a  small  body  of  a  darkish  colour, 
and  about  the  size  of  a  cherry-stone,  which  is  placed  between 
the  posterior  extremities  of  the  two  thalami  on  the  dorsal 
aspect  of  the  mesencephalon  (Fig.  206).  It  occupies  the 
depression  between  the  two  superior  quadrigeminal  bodies, 
and  is  shaped  like  a  fir-cone.  Its  base,  which  is  directed 
anteriorly,  is  attached  by  means  of  a  hollow  stalk  or  peduncle. 
This  stalk  is  separated  into  a  dorsal  and  a  ventral  part  by  a 
continuation  into  it  of  a  pointed  recess  of  the  cavity  of  the 
third  ventricle.  The  dorsal  part  of  the  stalk  becomes  con- 
tinuous on  each  thalamus  with  the  taenia  thalami ;  the  ventral 
part  is  folded  round  a  narrow  but  conspicuous  cord-like  band 
of  white  fibres  {posterior  conwiissure)  which  crosses  the  median 
plane  immediately  below  the  base  of  the  pineal  body. 

Commissura  Anterior  Cerebri.- — In  the  anterior  part 
of  the  cleft  between  the  two  thalami,  and  immediately 
anterior  to  the  columns  of  the  fornix,  a  round  bundle  of 
white  fibres  will  be  seen  crossing  the  median  plane.  This 
is  the  anterior  co?n7nissure.  It  is  very  much  larger  than  the 
posterior  commissure,  and  will  be  afterwards  followed  towards 
the  temporal  lobe,  in  which  the  greater  part  of  it  ends. 

Ventriculus  Tertius. — This  name  is  given  to  the  deep 
narrow  cleft  between  the  two  thalami.  It  is  deeper  anteriorly 
than  posteriorly,  and  extends  from  the  pineal  body  posteriorly 
to  the  anterior  commissure  and  lamina  terminalis  anteriorly. 
Its  Jloor  is  formed  by  the  parts  already  studied  within  the 
interpeduncular  fossa  on  the  base  of  the  brain,  viz.,  the  tuber 
cinereum,  the  corpora  mamillaria,  and  the  grey  matter  of  the 
substantia  perforata  posterior,  and  also,  more  posteriorly,  by  the 
tegmenta  of  the  cerebral  peduncles.  Anteriorly,  it  is  bounded 
by  the  lamina  terminalis  and  the  anterior  commissure ;  whilst 


504 


THE  BRAIN 


its  lateral  walls  are  formed  by  the  medial  surfaces  of  the 
two  thalami.  A  little  anterior  to  the  middle  of  the  ventricle 
the  cavity  is  crossed  by  the  massa  intermedia^  which  connects 
the  thalami  with  each  other,  and  anterior  to  this  the  column 
of  the  fornix  is  seen  descending  in  the  lateral  wall.  At  first 
the  column  is  distinct  and  prominent,  but  as  it  approaches 
the    corresponding    corpus    mamillare    it    gradually   becomes 

Sulcus  hypothalamicus        Corpus  callosum 

Massa  intermedia 
'    Thalamus 


Chorloid  plexus 

Column 

of  fornix 


For.  interventriculare 
Septum  pellucidum 

Genu , 


Tsenia  thalami 
'      Mesencephalon 

'     Pineal  body 

'      /  Quadrigeminal  bodies 
Splenium 
J  Aquaeductus  cerebri 

.-     Culmen  monticuli 


Declive  monticuli 


Anterior  _  - ' 
commissure  ,.-'' 

Corpus  mamillare  ' ' '       ,  - 
Lamina  terminalis  ' 

Optic  nerve  ' 
Hypophysis  •'  ', 

Tuber  cinereum 
Oculo-motor  nerve 


Folium 
vermis 


Pons       /    ; /  / 

Anterior  medullary  velum    /  /  ^ 

Ventricle  iv. .'   ^' 

Medulla  oblongata  ' 

Chorioid  plexus 

in  Ventricle  iv. 


Uvula 
Central  lobule 
Nodule 


Fig.  207. — Median  section  through  the  Corpus  Callosum,  Third  Ventricle, 
Mesencephalon,  Pons,  Cerebellum,  and  Medulla  Oblongata. 

more  and  more  sunk  in  the  grey  matter  on  the  side  of  the 
ventricle. 

The  roof  oi  the  third  ventricle  is  formed  by  a  thin  epithelial 
layer  which  stretches  across  the  median  plane,  from  the  one 
tsenia  thalami  to  the  other,  and  is  continuous  with  the 
remainder  of  the  epithelial  lining  of  the  cavity.  It  is  applied 
to  the  under  surface  of  the  tela  chorioidea,  which  overlies  the 
ventricle,  and  is  invaginated  into  the  cavity  by  the  chorioid 
plexuses  which  hang  down  from  the  under  surface  of  that 
fold  of  pia  mater.  In  the  removal  of  the  tela  chorioidea 
the  thin  epithelial  roof  was  torn  away. 

The  third  ventricle  communicates  freely  with  the  lateral 


THE  CEREBRUM  5^5 

ventricles,  and  also  with  the  fourth  ventricle.  The  aqu(B- 
ductus  cerebri  {Sylvius),  a  narrow  channel  which  tunnels  the 
mesencephalon,  brings  it  into  communication  with  the  fourth 
ventricle.  The  opening  of  this  canal  will  be  seen  at  the 
posterior  part  of  the  floor  of  the  ventricle,  immediately  below 
the  posterior  commissure.  The  inter-centricular foramen,  which 
puts  it  into  communication  with  the  two  lateral  ventricles,  is  a 
Y-shaped  aperture  which  lies  at  the  anterior  part  of  the  ventricle, 
and  its  two  diverging  limbs  pass  laterally  and  slightly  upwards, 
between  the  most  prominent  parts  of  the  columns  of  the  fornix 
and  the  anterior  tubercles  of  the  thalami.  They  are  usually 
large  enough  to  admit  a  crow-quill,  and  through  them  the 
epithelial  lining  of  the  three  ventricles  becomes  continuous. 

FORAMEN  INTERVENTRICULARE 


ANTR.COM 


MASSA   INTERMEDIA 


.RECESSUS 
OPTIC  CH,ASMA^,.,^,^;_^  _(S^S'UPRAPINEAUS 

RECESSUS   PINEALIS 
POSTR.  COM. 
AQU/EDUCTUS 
CEREBRI 
HYPOPHYSIS 


Fig.  208. — Diagrammatic  outline  of  the  Third  Ventricle 
as  viewed  from  the  side. 

From  each  lateral  part  of  the  interventricular  foramen  a 
distinct  groove  passes  posteriorly,  on  the  lateral  wall  of  the 
ventricle,  to  the  mouth  of  the  aqusductus  cerebri.  It  is 
termed  the  sulcus  hypothalamicus. 

The  outline  of  the  third  ventricle  is  seen  to  be  very  irregular  when 
it  is  viewed  from  the  side  in  a  median  section  through  the  brain  (Fig.  207), 
or  as  it  is  exhibited  in  a  plaster  cast  of  the  ventricular  system^  of  the  brain. 
It  presents  several  diverticula  or  recesses.  Thus,  in  the  anterior  part  of  the 
floor  there  is  a  deep  funnel-shaped  recess,  recesstis  infundibidi,  leading  dow^n, 
through  the  tuber  cinereum,  into  the  infundibulum  of  the  hypophysis. 
Another  recess,  recessus  opticus,  lies  above  the  optic  chiasma.  Posteriorly, 
two  additional  recesses  are  present.  One,  the  recesstis  pinealis,  passes 
posteriorly,  above  the  posterior  commissure  and  the  entrance  of  the  aquce- 
ductus  cerebri,  for  a  short  distance  into  the  stalk  of  the  pineal  body. 
The  second  is  placed  above  this,  and  is  carried  posteriorly  for  a  greater 
distance.  Its  walls  are  epithelial,  and  therefore  it  cannot  be  seen  in  an 
ordinary  dissection.      It  is  termed  the  recessus  suprapinealis. 

Dissection. — The  further  study  of  the  cerebral  hemispheres  should  be 
postponed  until  after  the  examination  of  the  mid-brain  or  mesencephalon. 
The  membranes  should  be  removed  from  the  upper  surface  of  the  cere- 
bellum,   and    the    prominent  anterior   part    of   that   organ   may   then    be 


5o6  THE  BRAIN 

pulled  posteriorly  to  expose,  as  far  as  possible,  the  corpora  quadrigemina, 
i.e.  the  four  rounded  eminences  on  the  dorsal  aspect  of  the  mesencephalon. 
In  doing  this,  care  should  be  taken  to  secure  and  preserve  the  slender 
trochlear  nerve  which  issues  from  a  lamina,  called  the  anterior  medullary 
velum,  immediately  below  the  inferior  pair  of  quadrigeminal  bodies,  and 
winds  round  the  lateral  side  of  the  pedunculus  cerebri. 


THE  MESENCEPHALON. 

The  mesencephalon  is  the  stalk  which  occupies  the  aperture 
of  the  tentorium  cerebelli,  and  connects  the  cerebral  hemi- 
spheres with  the  parts  in  the  posterior  cranial  fossa.^  It  is 
about  three-quarters  of  an  inch  long,  and  it  consists  of 
a  dorsal  part,  the  lajuina  quadrigemina^  and  a  much  larger 
ventral  part,  which  is  formed  by  the  two  IdiTge.  pedunculi  cerebri 
In  the  undissected  brain  the  lamina  quadrigemina  is  com- 
pletely hidden  from  view  by  the  splenium  of  the  corpus 
callosum,  which  projects  posteriorly  over  it,  and  also  by 
the  superimposed  cerebral  hemispheres.  The  pedunculi 
cerebri,  however,  can  be  seen,  to  some  extent,  at  the  base  of 
the  brain,  where  they  bound  the  posterior  part  of  the  inter- 
peduncular fossa.  The  mesencephalon  is  tunnelled  from 
below  upwards  by  a  narrow  passage  called  the  aquseductus 
cerebri  (Sylvius).  This  channel  lies  much  nearer  the  dorsal 
than  the  ventral  surface. 

Lamina  Quadrigemina. — The  dorsal  surface  of  the  lamina 
quadrigemina  is  raised  into  four  eminences  or  colliculi.,  two 
superior  and  two  inferior,  which  are  called  the  corpora  quadri- 
gemina. Each  colliculus  is  composed,  for  the  most  part,  of 
grey  matter,  although  each  has  a  superficial  coating  of  white 
fibres.  The  superior  pair  are  larger  and  broader  than  the 
inferior  pair.,  but  they  are  not  so  well  defined  nor  yet  so 
prominent. 

A  longitudinal  and  a  transverse  groove  separate  the  quadri- 
geminal bodies  from  each  other.  The  longitudinal  groove 
occupies  the  median  plane,  and  extends  upwards  as  far  as  the 
posterior  commissure.  From  its  lower  end  a  short  but  well- 
defined  narrow  band  of  white  fibres,  the  frenulum  veli,  passes 
to  the  anterior  medullary  velum,  a  lamina  placed  immediately 
below  the  inferior  pair  of  quadrigeminal  prominences.     The 

^  If  the  mesencephalon  was  divided,  when  the  brain  was  removed,  the 
divided  parts  must  be  fixed  together  with  pins  while  the  superficial  characters 
are  being  studied. 


THE  MESENCEPHALON  507 

upper  part  of  the  longitudinal  groove  is  occupied  by  the 
pineal  body.  The  transverse  groove  curves  round  posterior 
to  each  of  the  superior  pair  of  quadrigeminal  bodies  and 
separates  them  from  the  inferior  pair. 

Brachia  of  the  Corpora  Quadrigemina. — The  corpora 
quadrigemina  are  not  marked  off  from  the  side  of  the  mesen- 
cephalon, for  each  body  has  in  connection  with  it,  on  that 
aspect,  a  prominent  white  strand,  which  is  prolonged  upwards 
and  anteriorly  under  the  projecting  pulvinar.  The  strands 
are  called  the  brachia  of  the  corpora  quadrigemina,  and  they 
are  separated  from  each  other  by  a  continuation,  on  the  side 
of  the  mesencephalon,  of  the  transverse  groove  which  inter- 
venes between  the  two  pairs  of  bodies. 

Corpus  Geniculatum  Mediale. — Closely  connected  with 
the  brachium  of  the  inferior  quadrigeminate  body  will  be  seen 
the  corpus  geniculatum  mediale. 

It  IS  a  little  oval  emmence,  very                ,        corp:gen:lat. 
sharply   defined,   which   lies  on             /^^^^^^^__lateral  root. 
the  side  of  the  upper  part  of  the        ^  ^    ^--^^^rr---    opt,c  tract 
mesencephalon  under  shelter  of 
the  pulvinar  of  the  thalamus.  ^.^^^^     ^ ^       medial  root. 

Connections  of  the  Brachia    /-^W^Xx   Ncorp:gen  med. 


and    the    Origin  of   the   Optic    K^U^  \  Xsupr  brach.um 

.  ^^\  \  INFR.   BRACHIUM. 

Tract. — It  will  now  be  seen  that  \       -supr.quad:body 

the  brachia  are  intimately  con-  infr.quadbody. 

nected    with     the     optic     tract.      Fig.  209.— Diagram  of  the  Roots 
rr^,         .    /-     .        T        7  .  ^  of  the  Optic  Tract. 

The  inferior  brachium  proceed- 
ing upwards  from  the  lower  quadrigeminal  body  advances 
towards  the  corpus  geniculatum  mediale,  and  disappears 
from  view  under  cover  of  that  prominence.  Upon  the 
opposite  side  of  the  same  geniculate  body,  the  7nedial  root 
of  origin  of  the  optic  tract  arises,  and  the  appearance  is 
such  that  the  dissector  might  very  naturally  conclude  that 
the  inferior  brachium  and  the  root  of  the  optic  tract  are 
continuous.  That,  however,  is  not  the  case.  The  superior 
brachium  is  carried  upwards  and  anteriorly  between  the 
overhanging  pulvinar  and  the  corpus  geniculatum  mediale. 
It  partly  enters  the  corpus  geniculatum  laterale,  but  a  portion 
of  it  is  directly  continuous  with  the  lateral  root  of  the  optic 
tract. 

The  optic  tract  divides  at  its  posterior  end  into  a  medial  and  a  lateral 
root.       The  medial  root   enters    the  corpus  geniculatum   mediale.       The 


5o8 


THE  BRAIN 


lateral  root  is  partly  continuous  with  the  superior  brachium,  and  partly 
with  the  corpus  geniculatum  laterale  and  the  pulvinar.  The  superior 
quadrigeminal  body,  the  corpus  geniculatum  laterale,  and  the  pulvinar 
constitute  the  lower  visual  cetiti'es. 

Pedunculi  Cerebri  (O.T.  crura  cerebri). — The  pedunculi 
cerebri  constitute  the  chief  bulk  of  the  mesencephalon. 
When  viewed  from  below,  they  appear  as  two  large  rope- 
like  strands,  which  emerge,  close  together,  from  the  upper 
aspect  of  the  pons,  and  diverge  as  they  proceed  upwards  to 
enter   the  cerebral   hemisphere.     At   the  point  where   each 


Corpus  geniculatum  mediale 
Pulvinar 


Stria  terminalis 


Superior  brachium 
Inferior  brachium 


Corpus  geniculatum 
laterale' 


Basis  pedunculi 


Optic  tract 


Ant.  perforated 
substance 


Superior  quadrigeminal  body 

Inferior 
quadrigeminal  body 


°^^  Aquseductus  cerebri 


Posterior  perforated 

substance 

Corpus  mamillare 
—Tuber  cinereum 
Optic  chiasma 


Optic  nerve 


Fig.  2 id. — The  Origin  and  Relations  of  the  Optic  Tract. 
(Professor  Thane,  from  Quain's  Anatomy.) 

peduncle  disappears  into  the  corresponding  hemisphere,  it  is 
embraced,  on  its  lateral  side,  by  the  optic  tract  and  the  gyrus 
hippocampi. 

The  pedunculus  cerebri  of  each  side  consists  of  two  parts, 
viz.,  a  dorsal  tegmentum.^  which  is  prolonged  upwards  to  the 
region  below  the  thalamus;  and  a  ventral  basis  (O.T.  crusta)^ 
which  is  carried  upwards  into  the  internal  capsule  on  the 
lateral  side  of  the  thalamus.  When  the  base  of  the  brain 
is  examined  it  is  the  basis  pedunculi  which  is  seen.  It  is 
white  in  colour  and  streaked  in  the  longitudinal  direction. 
On  the  exterior  of  the  mesencephalon,  the  separation  between 
the  two  parts  of  the  pedunculus  cerebri  {i.e.  the  tegmentum 
and  the  basis  pedunculi)  is  indicated  by  a  medial  and  a 
lateral  groove  or  sulcus.     The  medial  sulcus  is  the  deeper 


THE  MESENCEPHALON  509 

and  more  distinct.  It  looks  into  the  interpeduncular  fossa, 
and  from  it  emerge  the  fila  of  the  oculo- motor  nerve. 
It  consequently  receives  the  name  of  the  sulcus  oculomotorius. 
The  lateral  sulcus  is  termed  the  sulcus  lateralis. 

Cut  Surface  of  the  Mesencephalon.  —  Much  nearer  the 
dorsal  than  the  ventral  surface  of  the  mesencephalon  the 
transversely  divided  aquceductics  cerebri  may  be  seen.  This 
narrow  passage  leads  from  the  fourth  ventricle  below  to  the 
third  ventricle  above.  It  is  surrounded  by  a  thick  layer 
of  grey  matter,  called  the  central  grey  77iatter  of  the 
aqueduct.  In  a  fresh  brain  this  is  always  very  conspicuous, 
and  in  its  midst  are  situated  the  nuclei  of  the  oculo- 
motor and  trochlear  nerves,  and  the  upper  motor  nucleus 
of  the  trigeminal  nerve,  although  of  course  these  cannot, 
except  in  very  favourable  circumstances,  be  detected  by 
the  naked  eye.  Below,  the  grey  matter  of  the  aqueduct 
is  continuous  with  the  grey  matter  spread  out  on  the 
anterior  wall  of  the  fourth  ventricle ;  whilst  above,  it  is  con- 
tinuous with  the  grey  matter  on  the  floor  and  sides  of  the 
third  ventricle. 

The  division  between  the  tegmentum  and  the  basis 
pedunculi,  on  each  side,  is  rendered  very  evident  by  a  con- 
spicuous lamina  of  dark  pigmented  matter  which  intervenes 
between  them.     This  is  termed  the  substaritia  nigra. 

Substantia  Nigra. — As  seen  in  transverse  section,  the  sub- 
stantia nigra  presents  a  somewhat  crescentic  outline.  It  is 
a  thick  band  interposed  between  the  basal  and  tegmental 
parts  of  the  pedunculi  cerebri,  and  it  consists  of  a  mass  of 
grey  matter  in  the  midst  of  which  are  large  numbers  of  pig- 
mented nerve  cells.  It  begins  below,  at  the  upper  border 
of  the  pons,  and  it  extends  upwards  into  the  subthalamic 
region.  Its  margins  come  to  the  surface  at  the  oculo-motor 
and  lateral  sulci,  and  its  medial  part  is  traversed  by  the 
emerging  fibres  of  the  oculo  -  motor  nerve.  The  surface 
turned  towards  the  tegmentum  is  concave  and  uniform ;  the 
opposite  surface  is  convex,  and  is  rendered  highly  irregular 
by  the  presence  of  numerous  slender  prolongations  of  its 
substance  into  the  basis  pedunculi. 

Basis  Pedunculi  (O.T.  crusta). — The  basis  pedunculi  is 
somewhat  crescentic  when  seen  in  section,  and  stands  quite 
apart  from  its  fellow  of  the  opposite  side.  It  is  composed  of 
a  compact  mass  of  longitudinally  directed  nerve  fibres  which 


5IO 


THE  BRAIN 


are  carried  upwards  into  the  internal  capsule.  The  inter- 
mediate third  or  more  of  each  basis  pedunculi  is  composed 
of  the  important  cerebrospinal  fasciculus  {O.T.  pyramidal  tract) 
as  it  descends  from  the  motor  area  of  the  cerebral  cortex, 
but  this  is  quite  indistinguishable  from  the  portions  of  the 
crusta  which  lie  on  either  side  of  it. 

Inferior  quadrigeminal  body- 


Grey  matter  of 
aqueduct 

Aquaeductus_|     _/\ 
cerebri    "    ?w 


^■Mesencephalic  root  of  fifth  nerve 

^''Nucleus  of  fourth  nerve 

^  ^  Inferior  brachium 

_,-- Medial  longitudinal  bundle 

"''  Medial 

'Ig  \        ^'lemniscus 


.W~'^r^ 


■\^  \   % 


Raphe 
Brachium  conjunctivum 


Substantia  nigra 


Basis  pedunculi 


Fig.  211. — Transverse  section  through  the  Mesencephalon  at  the  level  of  the 
inferior  quadrigeminal  body  :  the  right  side  only  is  reproduced.  The 
dravi^ing  is  taken  from  a  Weigert-Pal  specimen,  and  therefore  the  grey 
matter  is  pale  and  the  strands  of  white  matter  are  dark.  The  dark  colour 
of  the  substantia  nigra  is  not  evident  owing  to  the  thinness  of  the  section. 

Tegmentum. — Unlike  the  basis  pedunculi,  the  tegmentum 
is  undivided,  a  faint  line  in  the  median  plane,  termed  the 
median  raphe,  alone  indicating  its  bilateral  character.  To- 
wards the  dorsum  of  the  mesencephalon  it  is  fused  with  the 
bases  of  the  corpora  quadrigemina,  and  its  lateral  surfaces 
only  are  free. 

The  tegmentum  is  composed  of  an  admixture  of  grey  and  white  matter, 
constituting  what  is  termed  a  formatio  reticularis.  The  white  matter  is 
composed  of  fibres  running  both  transversely  and  longitudinally.     Certain 


THE  MESENCEPHALON 


511 


of  the  longitudinal  fibres  are  grouped  together  and  form  well-marked 
tracts,  which,  in  a  section  through  the  mesencephalon  of  a  fresh  brain,  can 
be  detected  by  the  naked  eye.  These  tracts  are:  (i)  the  medial  longi- 
tudinal bundles  ;  (2)  the  brachia  conjunctiva  ;  (3)  the  lemniscus. 

The  medial  longittidinal  hmdle  (Hgs.  211  and  212)  is  a  small  compact 
fasciculus  which  is  placed  upon  the  lateral  aspect  of  the  lower  portion  of 
the  central  grey  matter  of  the  aqueduct. 

The  brachia.  conjunctiva  (O.T.  superior  cerebellar  peduncles)   are  two 


Superior  quadrigeminal  body 
Tegmentum  I 

Inferior  brachiuin  i  I 

-Medial  geniculate  body  ' 

Lateral  geni-  ',  [ 

culate  bodyv  1  1 


Grey  matter  of  aqueduct 


— j-pAquacductus  cerebri 


\-__^_^-  Nucleus  of  third 

I  nerve 
f'^ — ^Medial  longi- 
''/,    f  tudinal  bundle 

—Red  nucleus 

-Fibres  of  brachium 
conjunct!  vum 


Optic  tract 

Basis  pedunculi 

Medial  lemniscus 


Substantia  nigra 


'  ^^.Filaof 

third  nerve 


Corpus  mamillare 


Fig.  212. — Section  through  upper  part  of  ]Mesencephalon  at  level  of  superior 
quadrigeminal  body.  The  drawing  is  taken  from  a  Weigert-Pal  specimen. 
The  dark  colour  of  the  substantia  nigra  is  not  evident  owing  to  the 
thinness  of  the  section. 


large  strands  which  are  continued  upwards  from  the  cerebellum  into  the 
mesencephalon.  By  pulling  away  the  margin  of  the  cerebellum,  where  it 
overlaps  the  lower  quadrigeminal  bodies,  these  brachia  will  be  seen  on  the 
surface  as  they  converge  in  an  upward  direction.  Stretching  across  the 
interval  between  them,  and  bringing  them  into  continuity  with  each  other, 
is  a  thin  lamina  called  the  anterior  medullaiy  velum.  When  the  brachia 
conjunctiva  reach  the  bases  of  the  inferior  quadrigeminal  bodies,  they 
sink  into  the  substance  of  the  mesencephalon,  and,  in  a  transverse  section 
through  the  lower  part  of  this  portion  of  the  brain,  they  may  be  seen  as  two 
white  strands,  semilunar  in  outline  and  placed  one  on  either  side  of  the 
grey  matter  of  the  aqueduct.  As  they  ascend,  they  gradually  assume  a 
deeper  [i.e.  a  more  ventral)  position  in  the  tegmental  part  of  the  mesen- 


512  THE  BRAIN 

cephalon,  and  they  decussate  with  each  other  across  the  median  plane  and 
proceed  upwards  to  the  red  nuclei. 

The  term  lemniscus  [O.T.  Jillet)  is  given  to  two  tracts  presenting  very 
different  connections.  The  medial  lemniscus  (Figs.  211  and  212)  is  a 
sensory  tract  passing  upwards  to  the  thalamus.  The  lateral  lemniscus 
belongs  to  the  auditory  apparatus,  and  is  a  part  of  a  chain  through  which 
the  cochlear  nuclei  establish  connection  with  the  inferior  quadrigeminal 
body  and  the  medial  geniculate  body.  The  lateral  lemniscus  can  be 
readily  detected  as  it  emerges  from  the  upper  part  of  the  lateral  sulcus  of 
the  mid-brain,  and  passes,  postero  -  superiorly,  to  the  lower  border  of  the 
inferior  quadrigeminate  body  and  inferior  brachium.  It  has  the  form  of 
a  raised  triangular  band  which  encircles  the  lateral  surface  of  the  upper 
end  of  the  brachivmi  conjunctivum  (Fig.  221). 

Within  the  upper  part  of  the  tegmentum  there  is  a  collection  of  nuclear 
matter  which  is  termed  the  nucleus  7'uber,  from  its  ruddy  appearance 
when  seen  in  section.  It  is  rod-like  in  form,  and  extends  upwards  into  the 
tegmental  region  below  the  thalamus.  In  transverse  section  it  presents  a 
circular  outline,  and  it  is  closely  associated  with  the  upward  prolongation 
of  the  fibres  of  the  brachia  conjunctiva  cerebelli.  The  brachium  conjunc- 
tivum cerebelli  is  an  efferent  tract  from  the  nucleus  dentatus  of  the 
lateral  hemisphere  of  the  cerebellum,  and  its  fibres  end  in  the  red  nucleus 
and  the  pulvinar  of  the  thalamus  of  the  opposite  side.  The  tegmentum 
of  the  pedunculus  cerebri  may  be  considered  to  consist  of  two  parts  :  viz. , 
a  lower  part,  which  is  subjacent  to  the  inferior  quadrigeminal  bodies, 
and  is  largely  occupied  by  the  decussation  of  the  brachia  conjunctiva 
cerebelli ;  and  an  upper  part,  subjacent  to  the  superior  quadrigeminal 
bodies,  which  is  traversed  by  the  emerging  bundles  of  the  third  nerve, 
and  contains  the  nucleus  ruber. 


BASAL  GANGLIA  OF  THE  CEREBRAL 
HEMISPHERES. 

The  basal  ganglia  of  the  cerebral  hemispheres  must  now 
be  examined.  They  are  the  caudate  and  lentiform  nuclei, 
which  together  form  the  corpus  striatum  ;  the  claustrum ; 
and  the  amygdaloid  nucleus.  With  these  it  is  necessary  to 
study  also  the  composition  of  the  thalamus  and  the  external 
and  internal  capsules. 

Dissection. — The  right  and  left  portions  of  what  remains  of  the  cerebrum 
should  be  separated  from  each  other  by  a  median  incision.  On  the  left 
portion  the  sulci  and  gyri  on  the  lower  surface  of  the  hemisphere  may  be 
examined,  if  this  has  not  been  done  already  on  another  specimen. 

A  series  of  sections  should,  in  the  next  place,  be  made  through  both  the 
right  and  left  portions  of  the  cerebrum,  with  the  view  of  displaying  the  basal 
ganglia.  On  the  right  side  remove  a  succession  of  thin  slices  by  carrying  a 
long  knife  in  a  horizontal  direction  through  the  parts  which  form  and  lie  below 
the  floor  of  the  central  part  of  the  lateral  ventricle.  It  is  not  advisable  to 
proceed  farther  down  than  the  level  of  the  anterior  commissure. 

On  the  left  side  of  the  brain  a  series  of  vertical-transverse  or  frontal 
sections  should  be  made  through  the  remaining  portion  of  the  cerebrum. 


BASAL  GANGLIA 


513 


Begin  by  cutting  off  the  portion  anterior  to  the  head  of  the  caudate  nucleus, 
and  then  proceed  posteriorly  until  the  posterior  part  of  the  thalamus 
is  reached.  One  of  the  sections  should  be  planned  to  pass  through 
the  anterior  commissure. 

Nucleus  Caudatus. — This  nucleus  has  already  been  partly 
examined    in  connection  with  the  lateral  ventricle,  into  the 

Claustrum 
Putamen 


Insula 


Genu  of  corpus  callosum 
Anterior  horn  of  lateral  ventricle  -- 
Head  of  caudate  nucleus  -- 

Anterior  limb  of  internal  capsule  - 
Cavum  septi  pellucidi 

Genu  of  internal  capsule  -' 
Globus  pallidus 
Fasciculus  thalamo-maniillaris 
Posterior  limb  of  internal  capsule 

Thalamus 

Retrolenticular  part 

of  internal  capsule 

Tail  of  caudate  nucleus 

Hippocampus 

Splenium 


Posterior  horn  of  lateral  ventricle  •'' 
Band  of  Vicq  d'Azj'^r  - 

Calcarine  fissure  - 
Tapetum  ' 


Optic  radiation 


Inferior  longitudinal  bundle 


Fig.  213. — Horizontal  section  through  the  Right  Cerebral  Hemisphere  at  the 
level  of  the  widest  part  of  the  lentiform  nucleus. 

cavity  of  which  it  bulges.  It  is  a  piriform  highly  arched 
mass  of  grey  matter,  which  presents  a  thick  swollen  head  or 
anterior  extremity,  and  a  long  attenuated  tail.  The  head 
projects  into  the  anterior  horn  of  the  lateral  ventricle,  whilst  its 
narrower  part  is  prolonged  laterally  and  posteriorly  on  the 
floor  of  the  central  part  of  the  ventricle,  where  it  is  separated 
from  the  thalamus  by  the  stria  terminalis.  Finally,  its  tail 
turns  downwards  and  then  anteriorly  into  the  inferior  horn 
VOL.  II — 33 


514 


THE  BRAIN 


of  the  lateral  ventricle,  on  the  roof  of  which  it  is  prolonged 
until  it  finally  joins  the  amygdaloid  nucleus.  The  caudate 
nucleus,  therefore,  presents  a  free  ventricular  surface  covered 
with  ependyma,  and  a  deep  surface  embedded  in  the  sub- 
stance of  the  hemisphere,  and  for  the  most  part  related  to  the 
internal  capsule. 

Owing  to  its  arched  form,  it  follows  that  in  horizontal 
sections,  below  a  particular  level,  it  is  cut  at  two  points,  and 
both  the  head  and  the  tail  must  be  looked  for  in  the  field  of 


,  Longitudinal  fissure 

Genu  of  corpus  callosum 


Corpus  callosum  (genu)' 

Longitudinal  fissure 


Caudate  nucleus 
Caudate  nucleus  (in  section) 
Anterior  horn  of  lateral  ventricle 


Fig.  214. — Frontal  section  through  the  Frontal  Lobes  of  the  Cerebrum.  The 
posterior  surface  of  the  anterior  part  of  the  cerebrum  is  depicted  so  that 
the  reader  is  looking  into  the  anterior  horns  of  the  lateral  ventricles  from 
behind. 


section  (Fig.  213).  In  frontal  sections  posterior  to  the  amyg- 
daloid nucleus  it  is  also  divided  at  two  places. 

Nucleus  Lentiformis. — This  mass  of  grey  matter  lies  on 
the  lateral  side  of  the  caudate  nucleus  and  the  thalamus,  and 
is,  for  the  most  part,  completely  embedded  within  the 
medullary  substance  of  the  cerebral  hemisphere.  It  does  not 
occupy  so  large  an  area  as  the  nucleus  caudatus.  Indeed,  it 
presents  a  very  close  correspondence  in  point  of  extent  with 
the  insula  on  the  surface. 

When  seen  in  horizontal  section  (Fig.  213)  it  presents  a 
shape  similar  to  that  of  a  biconvex  lens.      Its  medial  surface 


BASAL  GANGLIA 


515 


bulges  more  than  the  lateral  surface,  and  its  point  of  highest 
convexity  is  placed  opposite  the  stria  terminalis  or  the 
interval  between  the  caudate  nucleus  and  the  anterior  end 
of  the  thalamus. 

When  seen  in  frontal  section,  the  appearance  presented 
by  the  lentiform  nucleus  differs  very  much  in  the  different 
planes  of  section.      Figure  215  represents  a  section  through 

Corpus  callosum 

Longitudinal  fissure 


Lateral  ventricle       ;'      I 

Chorioid  plexus      |        ! 

Interventricular  foramen      1 
I 
Ria:ht  column  of  fornix 


Claustrum 


Fig.  21 


\  Internal  capsule 

'i  Lentiform  nucleus 

Caudate  nucleus 
Septum  pellucidum 

Frontal  section  through  the  Cerebral  Hemisphere  cutting  through 


the  anterior  part  of  the  lentiform  nucleus.      Seen  from  the  anterior  end. 

its  anterior  portion.  Here  it  is  semilunar  or  crescentic  in 
outline.  Further,  it  is  intimately  connected  with  the  head 
of  the  caudate  nucleus  by  bands  of  grey  matter  which  pass 
between  the  two  nuclei  and  break  up  the  anterior  part  of  the 
internal  capsule.  It  is  due  to  the  ribbed  or  barred  appear- 
ance which  is  presented  by  such  a  section  as  this  that  the 
term  corpus  striatum  is  given  to  the  two  nuclei. 

When  the  section  is  made  in  a  more  posterior  plane,  the 
divided  lentiform  nucleus  assumes  an  altogether  different 
shape,  and  is  seen  to  be  completely  cut  off  from  the  caudate 


5i6 


THE  BRAIN 


nucleus  by  the  internal  capsule  (Fig.  216).  It  is  now  tri- 
angular or  wedge-shaped.  Its  base  is  turned  towards  the 
external  capsule,  the  claustrum,  and  the  insula ;  its  medial 
surface  is  applied  to  the  internal  capsule ;  whilst  its  inferior 
surface  is  directed  downwards  towards  the  base  of  the  brain. 
But,  further,  two  white  laminae  are  now  evident,  the  external 


Longitudinal  fissure 


Chorioid  plexus 
Lateral  ventricle  V 


Claustrum 


Globus  pallidus' 

Amygdaloid  nucleus  /'       i 

Fasciculus  thalamo-mamillaris 

Substantia  perforata  anterior 


Corpus  callosum 
Fornix 


Tela  chorioidea  of 
^-'third  ventricle 

.^Caudate  nucleus 
—  Vena  terminalis 

,.  — Thalamus 
Ventricle  iii. 

T Chorioid  plexus 

— Internal  capsule 

-For,  interventriculare 
._  Column  of 
fornix 
-Optic  tract 

'-Anterior  commissure 
-Optic  nerve 


I  Olfactory  tract 
Optic  chiasma 

Infundibulum 
Column  of  fornix 


Fig.  216. — Frontal  section  through  the  Cerebral  Hemisphere  in  such  a  plane 
as  to  cut  the  three  parts  of  the  lentiform  nucleus  ;  the  posterior  cut 
surface  of  the  anterior  part  of  the  hemisphere  is  depicted. 

and  internal  medullary  lamincB,  which  traverse  its  sub- 
stance and  divide  it  into  three  zones.  The  lateral,  basal, 
and  larger  zone  is  termed  the  putamen  (Fig.  216).  It  is 
darker  in  colour  than  the  other  two  zones,  and  is  traversed  by 
fine  radiating  white  streaks.  The  two  medial  zones  are  of  a 
faint  yellowish  tint,  and  together  they  form  what  is  termed 
the  globus  pallidus  (Figs.  213  and  2 1 6).  The  putamen  has  a 
greater  antero-posterior  length  than  the  globus  pallidus.  It 
follows  from  this  that  it  alone  is  connected  with  the  head  of 


BASAL  GANGLIA 


517 


the  caudate  nucleus  by  the  intervening  bands  of  grey  matter 

(^"^ig-  215). 

The  nucleus  lentiformis  comes  to  the  surface  at  the 
substantia  perforata  anterior,  and  a  continuity  between  the 
grey  matter  forming  it  and  the  grey  cortex  of  the  brain  is 
thus  established. 

Caudate  nucleus 
Fronto-occipital  fasciculus   r    Thalamus 
Superior  longitudinal  fasciculus 


External  capsule 
Claustrum 


Insula 


Putamen  of  lenti- 
form  nucleus 

Globus  pallidus  of  /_ 
lentiform  nucleus  ! 


Stria  terminalis 

Upper  temporal 
sulcus 

Caudate  nucleus 

Inferior  cornu  of 
lateral  ventricle 


,, Corpus  callosum 
Chorioid  plexus 

Septum  pellucidum 

Fornix 

Chorioid  plexuses 

of  third  ventricle 

"Third  ventricle 
Red  nucleus 
Subthalamic  body 
Optic  tract 


Chorioid  plexus 

Hippocampal  fissure 

Collateral  fissure 

Cereljellum 
Brachium  pontis 
Pyramid  of  medulla  oblongata 

Fig.  217. — Oblique  frontal  section  of  brain  to  show  the  course  of  the  cerebro- 
spinal fibres.  The  internal  capsule  lies  between  the  lenticular  nucleus 
laterally  and  the  caudate  nucleus  and  thalamus  medially. 


Claustrum. — This  is  a  thin  plate  of  grey  substance  em- 
bedded in  the  white  matter  which  intervenes  between  the 
lentiform  nucleus  and  insula  (Figs.  213  and  216).  Followed 
in  an  upward  direction,  it  becomes  gradually  thinner  until  it 
ultimately  appears,  when  seen  in  section,  as  an  exceedingly 
delicate  grey  streak.     As  it   is   traced   downwards,   however, 

II — 33  ci 


5i8 


THE  BRAIN 


it  thickens  considerably,  and  at  the  base  of  the  brain  it 
comes  to  the  surface,  at  the  substantia  perforata  anterior, 
and  becomes  continuous  with  the  grey  matter  of  the  cerebral 
cortex.  Its  extent  corresponds  very  nearly  with  the  area 
occupied  by  the  insula,  and  its  lateral  surface  shows  ridges 
and  depressions  corresponding  to  the  insular  gyri  and  sulci. 

Capsula  Interna. — This  term  is  applied  to  the  broad  band 
of  white  matter  which  intervenes  between  the  lentiform 
nucleus  laterally,  and  the  thalamus,  stria  terminalis,  and 
caudate  nucleus  on  the  medial  side.     Anteriorly  it  is  much 


Fibres  of  medullary  laminae 
Upper  limit  of  int.  capsule      • — "^^ 
Area  in  relation     1        '        '  -. 
to  putamen 
Frontal  fibres  of 
corona  radiata 


Corona  radiata 


Area  in  relation  to  globus  pallidus 

)'^    -      Basis  pedunculi 

/  ^^       Lateral 

/  ,"'-',    geniculate  body 

Optic  radiations 

Medial  geni- 
V    culate  body 


Olfactory  bulb     ./ 
Anterior  commissure      , 
Optic  tract 
Corpus  mamillare   ,■' 
Oculo-motor  nerve 

Pyramidal  fibres    / 
Cut  surface  of  pons 

Pyramid   / 
Olive 


Trochlear  nerve 


Lateral  lemniscus 
Medial  lemniscus 
Brachium  pontis 


Fig.  2 1 8. — Dissection  of  Internal  Capsule  and  Pyramidal  Fibres. 

broken  up,  by  the  connecting  bands  of  grey  matter  which 
pass  between  the  head  of  the  caudate  nucleus  and  the 
anterior  part  of  the  putamen  of  the  lentiform  nucleus  (Fig. 
215),  but  more  posteriorly  it  forms  a  solid  white  mass  of 
nerve  fibres.  When  seen  in  horizontal  section,  the  internal 
capsule  is  bent  upon  itself  opposite  the  interval  between  the 
caudate  nucleus  and  the  thalamus  (Fig.  216).  This  bend, 
which  points  medially,  is  called  the  genu.  About  one-third 
of  the  internal  capsule  lies  anterior  to  the  genu,  and  this 
part  is  called  the  anterior  limb;  the  remaining  two-thirds, 
which  lie  posterior  to  the  genu,  constitute  the  posterior  limb. 

Connections  of  the  Internal  Capsule. — The  internal  capsule 
is  directly  continuous  below  with  the  basis  of  the  cerebral 


BASAL  GANGLIA  5i9 

peduncle.  The  dissector  can  easily  satisfy  himself  in  the 
specimens  before  him  of  this  continuity ;  it  is  apparent  in  the 
more  posterior  of  the  frontal  sections  which  he  has  made 
through  the  left  portion  of  the  cerebrum. 

It  has  been  mentioned  already  that  the  fibres  which  occupy  the  middle 
third  or  more  of  the  basis  of  the  cerebral  peduncle  belong  to  the  motor 
cerebro- spinal  fasciculus.  In  the  internal  capsule  these  fibres  occupy  the 
anterior  two-thirds  of  the  posterior  limb,  being  thus  placed  immediately 
posterior  to  the  genu.  The  fibres  which  constitute  the  medial  third  of  the 
basis  pedunculi  come  from  the  anterior  limb  of  the  internal  capsule  ;  whilst 
the  fibres  which  form  the  lateral  third  of  the  basis  pedunculi  are  situated 
in  the  posterior  limb. 

When  the  fibres  of  the  internal  capsule  are  traced  upwards,  they  are 
found  to  spread  out  in  a  radiating  manner  so  as  to  reach  the  various 
gyri  of  the  cerebral  hemispheres.  This  arrangement  is  termed  the 
corona  radiata.  As  the  fibres  of  the  corona  radiata  are  liberated  from 
the  internal  capsule,  and  spread  out  to  reach  their  destinations,  they  are 
intersected  by  fibres  of  the  corpus  callosum,  which  also  radiate  in 
every  direction  to  gain  the  cortex  of  the  cerebrum,  and  they  are  inter- 
sected also  by  bundles  of  association  fibres. 

Nuclei  of  the  Thalamus. — When  a  horizontal  section 
is  made  through  the  thalamus  in  a  fresh  brain,  or  in  one 
which  has  been  preserved  by  means  of  formaUn  or  a  chromic 
salt,  the  grey  matter  composing  it  is  seen  to  be  broken  up 
into  a  lateral,  a  medial,  and  an  anterior  nucleus  by  thin 
white  medullary  laminae. 

Capsula  Externa.— This  term  is  applied  to  the  thin 
stratum  of  w^hite  matter  which  intervenes  betw^een  the 
lentiform  nucleus  and  the  claustrum  (Figs.  213  and  216). 

Dissection.— T)i&  fasciculus  thalamo-mamillaris  and  the  anterior  com- 
missure should  now  be  followed,  as  far  as  this  is  possible,  m  what  remains 
of  the  right  half  of  the  cerebrum.     The  dissection  is  not  difficult. 

By  the  removal  of  the  remains  of  the  lentiform  nucleus  the  anterior  com- 
missure will  be  exposed  in  its  course  towards  the  temporal  lobe.  In  the  first 
instance,  it  passes  transversely,  then  postero-laterally  belo\y  the  putamen. 
Next  it  bends  suddenly  in  a  posterior  direction  above  the  inferior  horn  of 
the  lateral  ventricle  to  reach  the  medullary  centre  of  the  temporal  lobe. 
If  the  dissection  be  successfully  accomplished,  the  anterior  commissure 
will  be  seen  to  present  a  t^\^sted  or  rope-like  appearance. 

The  fasciculus  thalamo-mamillaris  may  be  traced  from  the  corpus 
mamillare  upwards  into  the  anterior  nucleus  of  the  optic  thalamus  by 
scraping  away  the  grey  matter  on  the  side  of  the  third  ventricle.  The 
continuity  between  the  column  of  the  fornix  and  the  corpus  mamillare 
should  at  the  same  time  be  established.  Within  the  corpus  mamillare  there 
is  a  nucleus  of  grey  matter. 

The  dissectors  have  now  examined  all  those  portions  of  the  brain  which 

lie  in  the  anterior  and  middle  cranial  fossee,  and  certain  terms,  not  hitherto 

mentioned  in   connection  with   the  various   structures  which   have  been 

studied,  now  require  consideration.      It  has  been  noted  already  that  the 

11—33  h 


520  THE  BRAIN 

part  of  the  brain  which  connects  the  lower  segment  in  the  posterior  fossa 
with  the  upper  segment  in  the  middle  and  anterior  fossa  is  called  the 
mesencephalon.  The  parts  above  the  mesencephalon  form  collectively 
the  prosencephalon,  and  the  mesencephalon  and  prosencephalon  together 
constitute  the  cerebrum. 

The  prosencephalon  itself  is  separable  into  two  main  parts,  the  telen- 
cephalon (end  brain),  and  the  diencephalon.  The  telencephalon 
includes  the  cerebral  hemispheres  with  their  grey  nuclei,  the  olfactory 
bulbs  and  tracts  and  the  associated  parts,  and  the  pars  optica  hypo- 
thalami; under  the  latter  term  are  included  the  tuber  cinereum,  the 
infundibulum,  the  hypophysis,  the  optic  tracts,  the  optic  chiasma,  and 
the  lamina  terminalis. 

The  diencephalon  iricludes  two  closely  associated  segments,  the  pars 
7najnillaris  hypothalami  and  the  thalamencephalon. 

The  pars  mamillaris  hypothalami  is  formed  by  the  mamillary  bodies 
and  those  portions  of  the  walls  of  the  third  ventricle  which  lie  below  the 
sulcus  hypothalamicus.  The  thalamencephalon  is  separated  into  the 
thalamtis  (O.T.  optic  thalamus),  the  metathalamus,  formed  by  the  two 
geniculate  bodies,  and  the  epithalamtis,  which  consists  of  the  pineal  body, 
the  habenula,  the  habenular  commissure,  and  the  trigonum  habenulae. 


THE  PARTS  OF  THE  BRAIN  WHICH  LIE  IN 
THE  POSTERIOR  CRANIAL  FOSSA. 

The  parts  which  he  below  the  tentorium  cerebehi  in  the 
posterior  cranial  fossa  are  the  medulla  oblongata^  the  pons^ 
and  the  cerebellu?n.  These  are  grouped  around  the  fourth 
ventricle  of  the  brain — a  cavity  which  communicates  with  the 
central  canal  of  the  medulla  spinalis  below  and  with  the 
aquseductus  cerebri  above ;  and  they  constitute  the  rhomben- 
cephalon or  hind  brain. 

Medulla  Oblongata. — This  is  the  continuation  of  the  spinal 
medulla  into  the  brain.  It  is  not  more  than  one  inch  in  length, 
and  may  be  reckoned  as  beginning  at  the  level  of  the  foramen 
magnum.  Thence  it  proceeds  upwards,  in  a  very  nearly  vertical 
direction,  and  ends  at  the  lower  border  of  the  pons.  At  first 
its  girth  is  similar  to  that  of  the  spinal  medulla,  but  it  rapidly 
expands  as  it  approaches  the  pons,  and  consequently  it 
presents  a  more  or  less  conical  appearance.  Its  anterior 
surface  lies  in  the  groove  on  the  basilar  portion  of  the 
occipital  bone,  whilst  its  posterior  aspect  is  sunk  into  the 
vallecula  of  the  cerebellum. 

The  medulla  oblongata  is  a  bilateral  structure,  and  this  is 
evident  even  on  an  inspection  of  its  exterior.  The  antero- 
median and  postero-median  sulci  on  the  surface  of  the  spinal 


MEDULLA  OBLONGATA 


521 


medulla  are  prolonged  upwards  on  the  anterior  and  posterior 
surfaces  of  the  medulla  oblongata. 

The  antero-medtan  g?'oove,  as  it  passes  from  the  spinal 
medulla  on  to  the  medulla  oblongata,  is  interrupted,  at  the 
level  of  the  foramen  magnum,  by  several  strands  of  fibres 
which  cross  the  median  plane  from  one  side  to  the  other. 
This  intercrossing  is  termed  the  decussatmi  of  the  pyramids. 
Above  this  level  the  furrow  is  carried  upwards  to  the  lower 


Optic  chiasma 

Optic  tract 

Corpus  geniculatum 

laterale  |i 
Corpus  geniculatum. 
mediale 
Substantia  perforat 
posterior 


Brachiuni 
pontis 


Restiform  body 

Olive 

Pyramid 

External 

arcuate  fibres 

Decussation  of- 
pyramids 


Optic  nerve 
Infundibulum 
Tuber  cinereum 

Corpus  mamillare 
Oculo-motor  nerve 

(HI.) 

Trochlear  nerve  (iv.) 
winding  round 
cerebral  peduncle 

Trigeminal  nerv^e  (v.) 
Abducent  nerve  (vi.) 
Facial  nerve  (vii.) 
Acustic  nerve  (viii.) 

Vago-glosso-pharyn- 
geal  nerve  (ix.  and  x.) 

Fila  of  hj'po- 
glossal  nerve  (xii.) 
cut  short 

Accessory 
nerve  (xi.) 

First  cervical  nerve 


Fig.  219. — Anterior  aspect  of  the  Medulla  Oblongata,  Pons,  and 
Mesencephalon  of  a  full-time  Foetus. 


border  of  the  pons.      There  it  expands  slightly,  and  ends  in 
a  blind  pit,  termed  i\\Q  fora?ne?i  ccecwn. 

The  postero-7nedian  fissure  is  carried  up  for  only  half  the 
length  of  the  medulla  oblongata.  Then  the  central  canal  of 
the  medulla  spinalis  becomes  the  fourth  ventricle  of  the  brain, 
and  as  it  expands  dorsally  it  pushes  aside  the  lateral  lips  of 
the  posterior  median  sulcus  till  the  epithelium  of  its  posterior 
wall  appears  on  the  surface,  in  the  triangular  interval  between 
the  diverging  posterior  columns   of  the   medulla  oblongata. 


522  THE  BRAIN 

where  it  forms  the  posterior  wall  or  roof  of  the  lower  part 
of  the  fourth  ventricle. 

The  surface  of  each  lateral  half  of  the  medulla  oblongata 
should  now  be  studied.  It  is  well,  however,  to  defer  the 
examination  of  the  medullary  part  of  the  floor  of  the  fourth 
ventricle  till  a  later  period.  The  dissector  has  already  noticed 
two  linear  rows  of  nerve  fila  issuing  from  and  entering  the 
medulla  oblongata  on  each  side.  The  anterior  row  consists 
of  the  roots  of  the  hypoglossal  and  the  uppermost  part  of  the 
anterior  root  of  the  first  cervical  nerve.  They  continue  up- 
wards on  the  medulla  oblongata  in  the  line  of  the  anterior 
nerve  roots  of  the  spinal  medulla,  and  they  emerge  along  the 
bottom  of  a  more  or  less  distinct  groove.  The  posterior  row  is 
formed  of  the  nerve  fila  of  the  accessory,  vagus,  and 
glosso- pharyngeal  nerves,  and  they  lie  in  series  with  the 
posterior  roots  of  the  spinal  nerves. 

By  these  two  rows  of  nerve  fila,  each  side  of  the 
medulla  oblongata  is  divided  into  three  districts,  viz.,  an 
anterior,  a  lateral,  and  a  posterior,  similar  to  the  surface  areas 
of  the  three  funiculi  on  the  side  of  the  medulla  spinalis.  At 
first  sight,  indeed,  they  appear  to  be  direct  continuations 
upwards  .of  those  portions  of  the  spinal  medulla ;  it  is  easily 
demonstrated,  however,  that  that  is  not  the  case,  and  that  the 
fibres  in  the  three  funiculi  of  the  medulla  spinalis  undergo  a 
rearrangement  as  they  are  traced  into  the  medulla  oblongata. 

Anterior  Area  of  the  Medulla  Oblongata — Pyramis. — The 
district  between  the  antero-median  furrow  and  the  row  of 
hypoglossal  nerve  fila  issuing  from  the  medulla  receives  the 
name  of  the  pyramid.  An  inspection  of  the  surface  is  almost 
sufficient  to  show  that  this  is  formed  by  a  compact  mass  of 
longitudinally  directed  fibres.  It  expands  somewhat,  and 
assumes  a  more  prominent  appearance  as  it  passes  upwards, 
and,  finally,  reaching  the  lower  border  of  the  pons,  it  becomes 
slightly  constricted  and  disappears  from  view  by  plunging  into 
that  structure.  The  pyramids  are  the  great  motor  strands  of 
the  medulla  oblongata. 

Although  the  pyramid,  at  first  sight,  appears  to  be  the 
continuation  upwards  of  the  anterior  funiculus  of  the  spinal 
medulla,  it  contains  within  itself  only  a  very  small  proportion 
of  fibres  which  occupy  that  funiculus.  This  will  be  at  once 
manifest  if  the  decussation  of  the  pyramids  is  examined.  For 
this  purpose  introduce  the  back  of  the  knife-blade  into  the 


MEDULLA  OBLONGATA 


523 


antero-median  furrow  below  the  decussation,  and  on  one  side 
push  in  a  lateral  direction  the  anterior  funiculus  of  the  medulla 
spinalis.  The  pyramid  will  then  be  seen  to  divide  into  two 
portions,  viz.,  a  small  strand  termed  the  fasciculus  cerebro- 
spinalis  anterior  (O.T.  direct  pyramidal  tract),  which  proceeds 
downwards  into  the  anterior  funiculus  of  the  spinal  medulla 


N.H.  Nucleus  hypoglossi 
N.V.  Vago-glosso-pharyn| 

nucleus. 
F.S.  Tractus  solitarius. 
N.A.  Nucleus  ambiguus. 


crossed  pyr.tr. 
dir.pyr.tr. 


Fig.  220. — Diagram  of  the  Decussation  of  the  Pyramids. 

(jNIodified  from  Van  Gehuchten. ) 

close  to  the  antero-median  furrow,  and  a  much  larger 
strand  called  the  fasciculus  cerebro spinalis  lateralis  (O.T. 
crossed  pyramidal  tract),  which,  at  this  level,  is  broken  up  into 
three  or  more  coarse  bundles  which  sink  posteriorly  and,  at 
the  same  time,  cross  the  median  plane  to  take  up  a  position 
in  the  opposite  lateral  funiculus  of  the  spinal  medulla,  close 
to  the  posterior  column  of  grey  matter.  It  is  the  inter- 
crossing of  the  corresponding  bundles  of  the  fasciculi  cerebro- 


524 


THE  BRAIN 


spinales  laterales  of  opposite  sides  which  produces  this  char 
acteristic  decussation. 

But  if  the  fasciculus  cerebrospinalis  anterior  of  the  anterior  funiculus  of 
the  spinal  medulla  is  alone  represented  in  the  corresponding  district  of  the 
medulla  oblongata,  it  may  be  asked  :  What  becomes  of  the  larger  lateral  part 
of  the  anterior  funiculus  of  the  spinal  medulla  in  the  medulla  oblongata  ?  It 
is  thrust  aside  by  the  decussating  bundles  of  the  fasciculus  cerebrospinalis 
lateralis,  and  thus  comes  to  occupy  a  deep  position  in  the  medulla  oblongata. 

Optic  tract 

Pedunculus  cerebri 

Corpus  geniculatum  laterale 

Pulvinar 

Corpus  geniculatum  mediale 

Superior  brachium 
Inferior  brachium 
Inferior  quadrigeminal  body 
Lateral  lemniscus 
Brachium  conjunctivum 
Taenia  pontis 

Brachium  pontis 


Restiform  body 

Ligula 

Olive 

Arcuate  fibres 

Clava 

Funiculus  cuneatus 

Rolandic  tubercle 

Lateral  district  of  medulla  oblongata 

Anterior  funiculus  of  spinal  medulla 


Fig.  221. — Lateral  view  of  the  Medulla  Oblongata,  Pons,  and 
Mesencephalon  of  a  full-time  Foetus. 


Lateral  Area  of  the  Medulla  Oblongata. — This  is  the 
district  on  the  surface  of  the  medulla  oblongata  which  is 
included  between  the  two  rows  of  nerve  fila,  viz.,  the  hypo- 
glossal fila  anteriorly,  and  the  fila  of  the  accessory,  vagus,  and 
glosso-pharyngeal  posteriorly.  It  presents  a  very  different 
appearance  in  its  upper  and  lower  parts.  In  its  lower 
portion  it  appears  to  the  eye  as  a  continuation  upwards 
of  the  lateral  funiculus  of  the  spinal  medulla ;  in  its  upper 
part  is  seen  the  striking  oval  prominence  named  the  o/we. 

The  lower  part  of  this  district,  however,  is  very  far  from 


MEDULLA  OBLONGATA 


525 


being  an  exact  counterpart  of  the  lateral  funiculus  of  the  spinal 
medulla.  It  has  been  noted  already  that  the  large  fasciculus 
cerebrospinalis  lateralis,  which  in  the  spinal  medulla  lies 
in  the  lateral  funiculus,  is  not  present  in  that  district  of  the 
medulla  oblongata ;  above  the  decussation  of  the  pyramids 
it  forms  the  chief  part  of  the  pyramid  of  the  opposite  side. 
Another  small  strand  of  fibres,  the  fasciculus  cerebello spinalis 
(O.T.  direct  cerebellar  tract),  prolonged  upwards  in  the  lateral 

Pineal  body 

Superior 
quadrigeminal  body 


Frenulum  veli 

Anterior 
medullary  velum 

Brachium 
conjunctivum 

Brachium  pontis 


Striae  medullares 

Area  acustica 

Ala  cinerea 

Funiculus  ciineatus 
Funiculus  gracilis 


Inferior 
quadrigeminal  body 


Cerebral  peduncle 

Pontine  part  of  floor 
of  ventricle  iv. 

Colliculus  facialis 
Area  acustica 

Restiform  body 
Trigonum  hypoglossi 

-Clava 

Rolandic  tubercle 
Funiculus  cuneatus 


Fig.  222. — Posterior  view  of  the  Medulla  Oblongata,  Pons,  and  Mesen- 
cephalon of  a  full-time  Fcxtus.  The  greater  part  of  the  roof  of  the 
fourth  ventricle  is  removed. 

funiculus  of  the  spinal  medulla,  gradually  leaves  this  portion 
of  the  medulla  oblongata.  This  tract  of  fibres  lies  on  the 
surface,  and  it  is  often  visible  to  the  naked  eye  as  a  white 
streak  inclining  obliquely  into  the  posterior  district  of  the 
medulla  oblongata  to  join  its  upper  part,  i.e.,  the  restiform 
body.  The  great  majority  of  the  remainder  of  the  fibres 
which  are  prolonged  upwards  from  the  lateral  funiculus  of 
the  spinal  medulla  disappear  from  the  surface  at  the  lower 
border  of  the  olive,  by  dipping  into  the  substance  of  the 
medulla  oblongata  under  cover  of  that  projection.  A  narrow 
band,  however,  is  carried  upwards  to  the  pons,  in  the  interval 


526  THE  BRAIN 

between  the  posterior  border  of  the  oHve  and  the  fila  of  the 
vagus  and  glosso-pharyngeal  nerves. 

The  olive  is  a  smooth  oval  projection,  which  occupies 
the  upper  part  of  the  lateral  area  of  the  medulla  oblongata. 
Its  long  axis,  which  is  vertical,  is  about  half  an  inch  long, 
and  its  upper  end  is  separated  from  the  lower  border  of  the 
pons  by  an  interval  or  groove. 

Posterior  Area  of  the  Medulla  Oblongata. — In  its  lower 
half  this  region  is  formed  by  the  cuneate  and  gracile  funiculi ; 
and  in  its  upper  half  it  is  formed,  medially,  by  the  ependymal 
roof  of  the  fourth  ventricle  and,  laterally,  by  the  diverging 
funiculi.^  It  is  separated  from  the  lateral  area  on  each  side 
by  the  row  of  fila  belonging  to  the  accessory,  vagus,  and 
glosso-pharyngeal  nerves. 

The  lower  part  of  the  posterior  area  corresponds  more  or 
less  closely  with  the  posterior  funiculi  of  the  spinal  medulla. 
It  will  be  remembered  that  in  the  cervical  part  of  the  spinal 
medulla  the  posterior  areas  on  each  side  is  divided  by  a 
distinct  septum  of  pia  mater  into  a  postero-median  strand  and 
a  postero- lateral  strand.  These  are  prolonged  upwards  into 
the  medulla  oblongata,  and  in  the  lower  part  of  the  posterior 
area  they  stand  out  distinctly,  and  are  separated  from  each 
other  by  a  continuation  upwards  from  the  medulla  spinalis 
of  the  postero-intermediate  sulcus.  In  the  medulla  oblongata 
these  strands  receive  different  names.  The  medial  one  is  called 
the  funiculus  gracilis^  whilst  the  lateral  one  is  designated  the 
funiculus  cuneatus.  Each  of  these  strands,  when  it  reaches 
the  lower  part  of  the  fourth  ventricle,  ends  in  a  slightly 
expanded  prominence.  The  swollen  extremity  of  the 
funiculus  gracilis  is  called  the  clava ;  it  is  thrust  aside  from 
its  fellow  of  the  opposite  side  by  the  opening  up  of  the 
central  canal  to  form  the  fourth  ventricle.  The  thickened 
end  of  the  cuneate  funiculus  receives  the  name  of  the 
tuberculum  cinereu77i^  but  it  is  in  the  young  brain  only  that  it 
is  well  marked. 

In  sections  through  this  region  of  the  medulla  oblongata, 
it  is  seen  that  the  prominences  produced  by  the  two  strands 
and  their  enlarged  extremities  are  in  a  great  measure  due  to  the 

^  The  dissector  should  note  that  the  lower  part  of  the  cavity  of  the  hind- 
brain,  i.e.  the  fourth  ventricle,  is  not  behind  but  in  the  upper  part  of  the 
medulla,  which  it  separates  into  dorsal  and  ventral  parts  ;  the  dorsal  part  forms 
a  portion  of  the  roof  of  the  ventricle,  whilst  the  ventral  part  forms  a  portion  of 
the  floor. 


MEDULLA  OBLONGATA  527 

presence  of  two  elongated  nuclei,  which  lie  subjacent  to 
them  and  gradually  increase  as  they  are  traced  upwards. 
These  are  termed  the  gracile  and  the  cuneate  nuclei,  and  it 
can  easily  be  shown  that  as  the  grey  matter  increases  in 
quantity  the  fibres  of  the  two  corresponding  strands  diminish 
in  number.  Indeed,  it  is  doubtful  if  any  of  their  fibres  are 
prolonged  upwards  beyond  the  level  of  the  nuclei. 

But  a  third  longitudinal  elevation  also  is  apparent  in  the 
lower  part  of  the  posterior  area  of  the  medulla  oblongata.  This 
is  placed  on  the  lateral  side  of  the  funiculus  cuneatus — between 
it  and  the  posterior  row  of  nerve  fila — and  it  has  no  counter- 
part in  the  posterior  funiculus  of  the  spinal  medulla.  It  is 
called  the  fimiculus  of  Rolando,  because  it  is  produced  by 
the  substantia  gelatinosa  Rolandi  approaching  the  surface. 
Extremely  narrow  below,  the  funiculus  of  Rolando  widens 
somewhat  as  it  is  traced  upwards,  and  it,  finally,  ends  in  an 
expanded  extremity  called  the  tubercle  of  Rolando.  The  thin 
layer  of  fibres  which  appear  on  the  surface  of  the  tubercle 
and  funiculus  of  Rolando  and  cover  the  substantia  gelatinosa 
Rolandi  in  this  position  belong  to  the  tractus  spinalis  (O.T. 
spinal  root)  of  the  trigeminal  nerve. 

The  restiform  body  forms  the  upper  part  of  the  posterior 
area  on  each  side.  It  lies  between  the  lower  part  of  the 
floor  of  the  fourth  ventricle  and  the  fila  of  the  vagus  and 
glosso-pharyngeal  nerves,  and  is  thrust  laterally  by  the  en- 
largement of  the  fourth  ventricle.  It  is  a  large  rope-like 
strand,  which  inclines  upwards  and  laterally,  and  then  finally 
takes  a  turn  posteriorly,  and  enters  the  cerebellum,  of  which 
it  constitutes  the  inferior  peduncle.  The  restiform  body,  there- 
fore, is  to  be  regarded  as  the  main  connection  between  the 
cerebellum,  above,  and  the  medulla  oblongata  and  medulla 
spinalis  below.  At  the  same  time,  it  must  be  understood 
that  it  is  not  formed  of  fibres  which  are  prolonged  into  it 
from  the  funiculus  gracilis  and  funiculus  cuneatus  of  its 
own  side.  It  is  true  that  a  surface  inspection  of  the 
medulla  oblongata  might  lead  very  naturally  to  this  supposi- 
tion, because  there  is  no  sharp  line  marking  it  off  from  the 
tubercles  of  these  strands. 

The  fibres  which  build  up  the  restiform  bodies  come  from  several  differ- 
ent sources.  It  will  be  sufficient  to  indicate  the  more  important  of  these — 
(i)  from  the  lateral  funiculus  of  the  spinal  medulla  through  the  fasciculus 
cerebellospinalis ;    (2)   from   the   cerebellum   as  the  cerebello-oliva}y  fbres 


528  THE  BRAIN 

which  go  to  the  opposite  inferior  olivary  nucleus ;  (3)  from  the  cuneate 
and  gracile  nuclei  of  both  sides  in  the  form  of  the  arcuate  ^bres. 

Fibrse  Arcuatss  Externse. — On  the  surface  of  the  medulla 
oblongata,  more  particularly  in  the  neighbourhood  of  the 
lower  border  of  the  olive,  a  number  of  curved  bundles  of  fibres, 
termed  the  external  arcuate  fibres^  may  be  noticed.  They 
vary  greatly  in  number  and  in  distinctness,  and  are  some- 
times so  numerous  as  to  cover  the  olive  almost  entirely. 
An  attentive  examination  will  show  that  they  come  to  the 
surface  in  the  antero-median  fissure  between  the  pyramids, 
in  the  groove  between  the  pyramid  and  the  olive,  and  some- 
times also  through  the  substance  of  the  pyramids.  But  at 
whatever  point  they  reach  the  surface,  the  majority  have  one 
destination,  viz.,  the  restiform  body — a  considerable  part  of 
which  they  form.  They  are  derived  from  the  cuneate  and 
gracile  nuclei  of  the  opposite  side. 

Dissection. — The  pyramid  of  one  side  should  now  be  carefully  raised. 
When  dislodged  from  its  bed  it  should  be  gently  pulled  upwards  towards 
the  pons.  In  this  way  its  entrance  into  the  pons  is  brought  very 
clearly  into  view.  Further,  numerous  arcuate  fibres  will  be  seen 
running  anteriorly  upon  the  medial  aspect  of  the  opposite  pyramid  to 
reach  the  surface,  and  the  ventral  edge  of  the  medial  lemniscus  will  be 
exposed  also. 

Pons. — The  pons  is  the  marked  prominence  on  the  base 
of  the  brain  which  is  interposed  between  the  medulla  ob- 
longata and  the  pedunculi  cerebri,  and  lies  anterior  to  the 
cerebellum.  It  is  convex  from  side  to  side,  as  well  as  antero- 
posteriorly,  and  the  transverse  streaks  on  its  surface  show 
that,  superficially,  it  is  composed  of  transverse  bundles  of 
nerve  fibres.  On  either  side  these  transverse  fibres  collect 
themselves  together  to  form  a  large  compact  strand  which 
sinks  postero-laterally  into  the  corresponding  hemisphere  of 
the  cerebellum.  This  strand  is  termed  the  brachium  pontis 
(O.T.  middle  cerebellar  peduncle). 

The  ventral  surface  of  the  pons  is  in  relation  to  the  basilar 
portion  of  the  occipital  bone  and  the  dorsum  sellae  of  the 
sphenoid  bone.  It  presents  a  median  groove  which  gradually 
widens  as  it  is  traced  upwards  (Fig.  219).  The  groove 
lodges  the  basilar  artery,  but  is  not  caused  by  that  vessel ; 
it  is  due  to  the  prominence  produced,  on  either  side,  by 
the  passage  downwards  through  the  pons  of  the  bundles 
of  fibres  which  form  the  pyramids  of  the  medulla  oblongata. 


CEREBELLUM  529 

Where  the  pons  becomes  the  brachium  pontis  the  large 
trigeminal  nerve  will  be  seen  entering  its  ventral  surface, 
nearer  its  upper  than  its  lower  border. 

With  the  exception  of  the  restiform  bodies,  the  whole  of  the 
medulla  oblongata  enters  the  lower  aspect  of  the  pons,  and  its 
constituent  parts  are  carried  upwards  within  it.  The  pedunculi 
cerebri  emerge  from  its  upper  aspect.  The  dorsal  surface  of 
the  pons  cannot  be  studied  at  present.  It  is  turned  towards 
the  cerebellum,  which  hides  it  from  view,  and  it  forms  the  upper 
part  of  the  anterior  boundary  or  floor  of  the  fourth  ventricle. 

Cerebellum. — The  cerebellum  is  distinguished  by  the 
numerous  parallel  and  more  or  less  curved  sulci  which 
traverse  its  surface  and  give  it  a  foliated  appearance.  As  in 
the  case  of  the  cerebral  hemispheres,  the  grey  matter  is 
spread  over  the  entire  surface,  whilst  the  white  matter  forms 
a  central  core  in  the  interior. 

The  cerebellum  consists  of  a  median  portion,  the  verifiis^ 
and  two  lateral  hemispheres.  The  distinction  between  these 
main  subdivisions  of  the  organ  is  not  very  evident  on  its 
superior  surface.  Anteriorly  and  posteriorly  there  is  a 
marked  deficiency  or  notch  in  the  median  plane  (Fig.  223). 
The  posterior  notch  is  smaller  and  narrower  than  the  anterior 
notch.  It  is  bounded  laterally  by  the  posterior  parts  of  the 
cerebellar  hemispheres,  and  anteriorly  by  the  vermis,  and 
it  is  occupied  by  the  falx  cerebelli.  The  attterior  notch  is 
much  wider  and,  when  viewed  from  above,  it  is  seen  to  be 
occupied  by  the  inferior  pair  of  quadrigeminal  bodies  and 
the  brachia  conjunctiva  cerebelli.  Its  sides  are  formed  by 
the  lateral  hemispheres,  and  the  posterior  end  is  bounded  by 
the  vermis. 

On  the  superior  surface  of  the  cerebellum  there  is  little 
distinction  to  be  noted  between  the  vermis  and  the  upper 
surface  of  each  lateral  hemisphere.  The  upper  surface  of 
the  vermis  forms  a  median  elevation,  from  which  the  surface 
slopes  gradually  downwards,  on  each  side,  to  the  margin 
of  the  hemisphere.  On  the  upper  surface  of  the  vermis  four 
regions  are  recognised.  Anteriorly,  at  the  posterior  end  of 
the  anterior  notch,  lies  the  central  lol>e,  and  prolonged  up- 
wards from  it  on  the  dorsal  surface  of  the  anterior  medullary 
velum,  between  the  brachia  conjunctiva,  are  a  few  folia  which 
constitute  the  lingula.  Posterior  to  the  central  lobe  is  the 
monticulus,  separable  into  two  parts — an  anterior  elevated  end, 

VOL.   II — 34 


530  THE  BRAIN 

the  culmen,  and  a  posterior  sloping  ridge,  the  declive.  Posterior 
to  the  dedive,  in  the  anterior  boundary  of  the  posterior  notch, 
lies  a  single  folium  called  iht  folium  vermis. 

On  the  inferior  surface  of  the  cerebellum,  the  distinction 
between  the  three  constituent  parts  of  the  organ  is  much 
better  marked.  On  that  aspect  the  hemispheres  are  full, 
prominent  and  convex,  and  they  are  separated  by  a  deep, 
median  hollow  which  is  continued  forwards  from  the  posterior 
notch.  This  hollow  is  termed  the  vallecula  cerebelli,  and  in  its  an- 
terior part  the  medulla  oblongata  is  lodged.  If  the  medulla  is 
forced  away  from  the  cerebellum,  and  the  lateral  hemispheres 
are  pulled  apart  so  as  to  expose  the  upper  boundary  of  the 
vallecula,  it  will  be  seen  that  this  is  formed  by  the  inferior 
surface  of  the  vermis,  and,  further,  that  the  vermis  is  separated, 
on  each  side,  from  the  corresponding  lateral  hemisphere  by  a 
distinct  furrow,  termed  the  sulcus  valleculce} 

If  the  margin  of  the  vermis,  where  it  forms  the  posterior 
boundary  of  the  anterior  notch  on  the  superior  aspect  of 
the  cerebellum,  is  gently  raised,  and  at  the  same  time  the 
mesencephalon  is  pulled  anteriorly,  two  strands  lying  upon 
the  dorsal  aspect  of  the  pons  will  be  seen.  These  are 
the  brachia  conjunctiva  cerebelli  (O.T.  superior  peduncles\ 
They  emerge  from  the  white  matter  of  the  cerebellum, 
converge  as  they  proceed  upwards,  and,  finally,  they  dis- 
appear under  the  inferior  quadrigeminal  bodies.  The  thin 
lamina  which  is  stretched  across  between  them  is  the  anterior 
medullary  velum.  It  is  continuous  below  with  the  white  core 
of  the  vermis,  and  it  helps  to  form  the  roof  of  the  upper 
part  of  the  fourth  ventricle.  From  its  dorsal  surface,  close 
to  the  inferior  quadrigeminal  body,  the  small  trochlear  nerves 
emerge. 

Certain  of  the  sulci  which  traverse  the  surface  of  the 
cerebellum,  deeper  and  longer  than  the  others,  map  out 
districts  which  are  termed  lobes.  The  most  conspicuous  of 
all  these  clefts  is  the  great  horizontal  sulcus. 

Great  Horizontal  Sulcus  of  the  Cerebellum. — The  great 
horizontal  sulcus  begins  anteriorly,  and  passes  round  the 
circumference  of  the  cerebellum,  cutting  deeply  into  its  lateral 
and  posterior  margins.      Anteriorly,  its  lips  diverge  from  each 

1  As  this  is  done  the  epithelial  roof  of  the  fourth  ventricle  and  its  covering 
of  pia  mater  will  be  torn  away,  and  the  lower  part  of  the  floor  or  anterior 
boundary  of  the  fourth  ventricle  will  be  displayed. 


CEREBELLUM 


531 


other  so  as  to  embrace  the  large  brachia  pontis  (O.T.  middle 
peduncles),  where  they  pass  into  the  interior  of  the  cere- 
bellum. The  great  horizontal  sulcus  divides  the  cerebellum 
into  an  upper  and  a  lower  part,  which  may  be  studied 
separately. 

Lobes  on  the  Upper  Surface  of  the  Cerebellum.— It  has  l^een  noted 
already  that  the  upper  surface  of  the  vermis  superior  is  sulxlivided.  The 
divisions  commencing  from  the  anterior  end  are  : — (i)  the  lingula  ;  (2)  the 
central  lobule  ;  (3)  the  culmen  monticuli  ;  (4)  the  declive  monticuli ;  (5)  the 
folium  vermis.     With  the  exception  of  the  lingula,  each  of  these  is  continuous 


Pons 


Mesencephalon 
I  Central  lobule 


Culmen  monticuli 


Anterior  crescentic  lobule 

Posterior  crescentic  lobule 


Declive  monticuli 

Folium  vermis 


Superior  semilunar 
lobule 


Inferior  semilunar  lobule 


Tuber  vermis 
Posterior  notch 


Fig.  223. — Upper  Surface  of  the  Cerebellum. 


on  either  side  with  a  corresponding  district  on  the  upper  surface  of  the  hemi- 
sphere, and  forms  with  these  districts  a  cerebellar  lobe.  Thus,  the  central 
lobule  is  prolonged  laterally  on  each  side  in  an  expansion  called  the  a/a  ; 
the  culmen  constitutes  a  median  connecting  piece  between  the  two  anterior 
crescentic  lobules  of  the  hemispheres  ;  the  declive  stands  in  the  same  relation 
to  the  posterior  crescentic  lobules  ;  and  the  folium  vermis  is  the  connecting 
band  between  the  superior  semilunar  lobules  of  the  hemispheres. 

Lingula. — The  Hngula  can  be  seen  only  when  the  posterior  boundary  of 
the  anterior  notch  is  pushed  posteriorly.  It  consists  of  four  or  five  small 
folia,  continuous  with  the  grey  matter  of  the  vermis,  prolonged  anteriorly 
on  the  surface  of  the  anterior  medullary  velum,  in  the  interval  between 
the  brachia  conjunctiva. 

Lobus  Centralis  with  its  Alse.— The  central  lobule  lies  at  the  posterior 


532 


THE  BRAIN 


end  of  the  anterior  notch,  and  is  largely  hidden  by  the  culmen.  It  is  a 
little  median  mass  which  is  prolonged  laterally  for  a  short  distance  round 
the  semilunar  notch  in  the  form  of  two  expansions,  termed  the  alcz. 

Lobus  Culminis. — The  culmen  monticuli  constitutes  the  summit  or 
highest  part  of  the  monticulus  of  the  vermis.  It  is  prolonged  laterally  on 
either  side  into  the  corresponding  hemisphere  as  the  anterior  crescentic 
lobule.  This  is  the  most  anterior  subdivision  on  the  upper  surface  of  the 
hemisphere.  The  two  anterior  crescentic  lobules,  with  the  culmen 
monticuli,  form  the  lohus  cuhninis  cerebelli. 

Lobus  Clivi. — The  declive  monticuli  lies  posterior  to  the  culmen,  from 


Central  lobule 
Brachium  conjunctivum 


Anterior  medullary  velum 


Ventricle  iv. 
/    Ala 


Brachium  pontis 
Posterior  medullary  \ 

velum  ^^ 


Nodule 


'Flocculus 


Great  horizontal 
sulcus 
Inferior  semilunar  lobule 

Lobulus  gracilis  \ 

Biventral  lobule 

Pyramid 
Uvula 


Great  horizontal 
sulcus 
/'  Lobulus  gracilis 

Biventral  lobule 


Tonsil 
Tuber  vermis 

Fig.  224.  — Lower  Surface  of  the  Cerebellum.  The  tonsil  on  the  right  side 
has  been  removed  so  as  to  display  the  posterior  medullary  velum  and 
the  furrowed  band. 


which  it  is  separated  by  a  distinct  fissure,  and  it  forms  the  sloping  part  or 
descent  of  the  monticulus  of  the  vermis.  On  each  side  it  is  continuous 
with  the  posterior  crescentic  lobule  of  the  lateral  hemisphere,  and  the  three 
parts  are  included  under  the  one  name  of  lobiis  clivi. 

The  two  crescentic  lobules  on  the  upper  surface  of  the  hemisphere  are 
frequently  described  together  as  the  quadrate  lobule. 

Lobus  Semilunaris  Superior  (O.T.  lobus  cacuminis).— The  folium 
vermis  forms  the  most  posterior  part  of  the  superior  portion  of  the 
vermis,  and  it  bounds  the  great  horizontal  fissure,  superiorly,  at  the 
posterior  notch.  It  is  a  single  folium,  the  surface  of  which  may  be 
smooth  or  beset  with  rudimentary  secondary  folia,  and  it  is  the  connecting 
link  between  the  two  superior  semilunar  lobules  of  the  hemispheres — 


CEREBELLUM 


533 


the  three  parts  constituting  the  lobus  semihmaris  superior.  As  the  folium 
vermis  is  traced  laterally  into  the  semilunar  lobule  of  the  hemisphere, 
it  is  found  to  expand  greatly.  The  result  of  this  is  that  the  lobus 
semilunaris  superior  on  each  side  forms  an  extensive  foliated  district 
bounding  the  posterior  part  of  the  great  horizontal  sulcus  superiorly. 

Lobes  on  the  under  surface  of  the  Cerebellum.— The  connection 
between  the  several  portions  of  the  inferior  part  of  the  vermis,  and  the 
corresponding  districts  on  the  under  surface  of  the  two  hemispheres  is  not 
nearly  so  distinct  as  in  the  case  of  the  superior  part  of  the  vermis  and  the 
lobules  on  the  upper  surface  of  the  hemispheres. 

Proceeding  postero-anteriorly  the  following  subdivisions  of  the  inferior 
part  of  the  vermis  are  recognised— (i)  the  tuber  vermis,  (2)  the  pyramid, 
(3)  the  uvula,  and  (4)  the  nodule. 

On  the  under  surface  of  the  hemisphere  there  are  five  lobules  mapped 
out  by  intervening  sulci.  These  are— (i)  \he  flocculus,  a  little  lobule  lying 
on  the  brachium  pontis  ;  {2)  the  biventral  lobule,  which  lies  immediately 


Culmen 


Central  lobule 


Declive 


Tuber  vermis 


PjTamid 


Lingula  on  the 
anterior  medul- 
lary velum 


Uvula/ 


'■•'■W 


Nodule 


Fig.  225. — IMedian  section  through  the  Vermis  of  the  Cerebellum. 
( From  Gescenbaur. ) 


posterior  to  the  flocculus,  and  is  partially  divided  into  two  parts  by  a  fissure 
which  traverses  its  surface  ;  (3)  the  tonsil,  a  rounded  lobule,  which  bounds 
the  vallecula  on  the  medial  side  of  the  biventral  lobule  ;  (4)  the  inferior 
semilunar  lobule,  placed  posterior  to  the  biventral  lobule,  and  bounding  the 
great  horizontal  sulcus  inferiorly. 

These  lobules  of  the  hemispheres,  with  the  corresponding  portions  of 
the  inferior  part  of  the  vermis,  constitute  the  lobes  on  the  under  aspect  of 
the  cerebellum. 

Lobus  Noduli.— The  lobus  noduli  comprises  the  nodule  and  the  flocculus 
of  either  side  with  an  exceedingly  delicate  connecting  lamina  of  white 
matter,  termed  the  posterior  medullary  velum. 

The  velum  cannot  be  properly  seen  at  present,  but  it  will  be  exposed  at 
a  later  stage  of  the  dissection. 

Lobus  Uvulse.— The  uvula  is  a  triangular  elevation  placed  between  the 
two  tonsils.  It  is  connected  across  the  sulcus  valleculce  with  each  tonsil 
by  a  low-lying  ridge  of  grey  matter  which  is  scored  by  a  few  shallow 
furrows,  and  in  consequence  termed  iht  furrowed  band.  The  two  tonsils 
and  the  uvula  form  the  lobus  uvula. 

To  see  the  furrowed  band  it  will  be  necessary  to  remove  the  tonsil  on 
one  side,  when  the  posterior  medullary  velum  also  will  be  exposed. 


534  THE  BRAIN 

Lobus  Pyramidis. — The  pyramid  is  connected  with  the  biventral 
lobule  on  each  side  by  a  faint  ridge  which  crosses  the  sulcus  vallecula. 
The  term  lobus  pyramidis  is  given  to  the  three  lobules  which  are  thus 
associated  with  each  other, 

Lobus  Tuberis. — The  tuber  vermis,  which  forms  the  most  posterior  part 
of  the  vermis,  is  composed  of  several  folia,  which  run  directly  into  the 
inferior  semilunar  lobule  on  each  side.  The  three  parts  of  the  lobus  tuberis 
are  thus  linked  together.  The  inferior  semilunar  lobule  is  traversed  by 
two,  or  it  may  be  three,  curved  fissures.  The  most  anterior  of  these  cuts 
off  a  narrow,  curved  strip  of  cerebellar  surface  called  the  lobtihis  gracilis. 

Dissection.-  K  median  section  should  now  be  made  through  the  vermis 
of  the  cerebellum  and  the  two  medullary  vela  into  the  cavity  of  the  fourth 
ventricle.  When  the  two  parts  of  the  cerebellum  are  drawn  slightly 
asunder,  a  view  of  the  fourth  ventricle  is  obtained  ;  further,  the  connections 
of  the  two  medullary  vela  and  the  arrangement  of  the  peduncles  of  the 
cerebellum  can  be  more  clearly  understood. 

Arbor  Vitse  Cerebelli. — The  cut  surface  of  the  cerebellum 
presents  a  very  characteristic  appearance.  The  grey  matter 
on  the  surface  stands  out  distinctly  from  the  white  matter  in 
the  interior.  Further,  the  complete  manner  in  which  the 
surface  is  cut  up  by  the  sulci  into  secondary  and  tertiary  folia 
is  seen.  The  central  mass  of  white  matter  in  the  vermis  is 
termed  the  corpus  medullare.  From  this,  prolongations  pass 
into  the  various  lobules,  and  these  give  off  branches  to  supply 
each  folium  with  a  central  white  stem  or  core.  The  term 
arbor  vit(E  is  applied  to  the  appearance  which  consequently 
results  when  a  section  is  made  through  the  cerebellum. 

Cerebellar  Peduncles. — The  cerebellar  peduncles  are  the 
structures  which  connect  the  cerebellum  with  the  medulla 
oblongata,  the  pons  and  the  mid-brain.  They  are  three  in 
number  on  each  side — viz.,  the  middle,  the  superior,  and 
the  inferior.  They  are  all  directly  connected  with  the  white 
medullary  centre  of  the  cerebellum,  and  are  composed  ot 
fibres  which  emerge  from  or  enter  the  white  central  sub- 
stance of  the  organ. 

The  middle  peduncle  is  the  brachium  pontis,  and  is  much 
the  largest  of  the  three.  It  is  formed  by  the  transverse 
fibres  of  the  pons,  and  it  enters  the  cerebellar  hemisphere  on 
the  lateral  side  of  the  other  two.  The  lips  of  the  anterior 
part  of  the  great  horizontal  sulcus  are  separated  widely  from 
each  other  to  give  it  admission. 

The  inferior  peduncle  is  simply  the  restiform  body  of  the 
medulla  oblongata.  Leaving  the  dorsum  of  the  medulla 
oblongata  it  turns  sharply  posteriorly  and  enters  the  cerebellum 
between  the  other  two  peduncles. 


MEDULLARY  VELA  535 

The  superior  peduncles  are  the  brachia  conjunctiva  of 
the  cerebellum.  They  are  composed  of  fibres  which  come,  for 
the  most  part,  from  the  nucleus  dentatus  of  the  cerebellar 
hemisphere.  As  they  issue  from  the  cerebellum,  the 
peduncle  lies  close  to  the  medial  sides  of  the  corresponding 
middle  peduncles.  They  then  proceed  upwards  towards  the 
inferior  pair  of  quadrigeminal  bodies.  At  first  they  form  the 
lateral  boundaries  of  the  upper  part  of  the  fourth  ventricle, 
but  they  converge,  as  they  ascend  on  the  dorsal  aspect  of  the 
pons,  so  that  ultimately  they  overhang  the  fourth  ventricle 
and  enter  into  the  formation  of  its  roof.  They  disappear 
under  cover  of  the  quadrigeminal  bodies,  and  their  course 
in  the  mesencephalon  has  been  described  already  (p.  511). 

Medullary  Vela. — The  medullary  vela  are  closely  associated 
with  the  peduncles.  They  consist  of  two  thin  laminae  of 
white  matter  which  are  projected  out  from  the  white  central 
core  of  the  cerebellum.  The  anterior  medullary  velum  stretches 
across  the  interval  between  the  two  brachia  conjunctiva 
(superior  peduncles),  with  the  medial  margins  of  which  it  is 
directly  continuous.  It  is  triangular  in  form,  and  is  con- 
tinuous below  with  the  white  matter  of  the  cerebellum. 
Spread  out  on  its  dorsal  surface  is  the  tongue-shaped  prolonga- 
tion of  grey  matter  from  the  cortex  of  the  cerebellum  which 
is  termed  the  lingula^  and  issuing  from  its  substance,  close 
to  the  inferior  quadrigeminal  bodies,  are  the  two  trochlear 
nerves. 

1l\\.^ posterior  medullary  velu7n  is  somewhat  more  complicated 
in  its  connections.  It  presents  the  same  relation  to  the 
nodule  that  the  anterior  velum  presents  to  the  lingula.  It  is 
a  wide  thin  lamina  of  white  matter — so  thin  that  it  is 
translucent — which  is  prolonged  out  from  the  white  centre 
of  the  cerebellum  above  the  nodule.  From  the  nodule  it 
stretches  laterally  to  the  flocculus,  thereby  bringing  these 
two  small  portions  of  the  cerebellum  into  association  with 
each  other.  Where  it  issues  from  the  white  matter  of  the 
cerebellum  it  might  almost  be  said  to  be  in  contact  with  the 
anterior  medullary  velum,  but  as  the  two  laminae  are  traced 
anteriorly  they  diverge  from  each  other  :  the  anterior  velum  is 
carried  upwards  between  the  brachia  conjunctiva  of  the  cere- 
bellum, whilst  the  posterior  medullary  velum  turns  downwards, 
round  the  nodule,  and  ends  in  a  slightly  thickened  free 
crescentic  edge.     The  cavity  of  the  fourth  ventricle  is  carried 


536  THE  BRAIN 

posteriorly  between  the  two  vela,  which  form  a  tent-like  roof 
for  it. 

Isthmus  Rhombencephali. — If  the  dissectors  examine  the 
rhombencephalon  from  the  side  they  will  recognise  that  there 
is  a  region  below  the  lamina  quadrigemina  and  above  the 
cerebellum  which  is  bounded  dorsally  by  the  anterior 
medullary  velum,  laterally  by  the  brachia  conjunctiva,  and 
ventrally  by  the  upper  part  of  the  pons ;  it  is  to  this  region 
that  the  term  isthmus  rhombencephali  is  applied.  It  contains 
the  upper  part  of  the  fourth  ventricle. 

Ventriculus  Quartus. — This  cavity  is  somewhat  rhomboidal 
in  form.  Below,  it  tapers  to  a  point  and  becomes  continuous 
with  the  central  canal  of  the  lower  part  of  the  medulla 
oblongata ;  above,  it  narrows  in  a  similar  manner  and  is 
continued  into  the  aquasductus  cerebri  of  the  mid-brain. 
The  anterior  wall  is  termed  the  floor^  and  is  formed  by  the 
dorsal  surface  of  the  ventral  part  of  the  upper  portion  of 
the  medulla  oblongata  and  by  the  dorsal  surface  of  the  pons. 
The  posterior  wall  is  called  the  roof.  On  either  side  a 
narrow  pointed  prolongation  of  the  ventricular  cavity  is 
carried  laterally,  from  its  widest  part,  round  the  upper  part 
of  the  corresponding  restiform  body.  This  is  termed  the 
lateral  recess  {¥ig.  222,  p.  525).  It  is  seen  to  the  greatest 
advantage  when  the  cerebellum  is  divided  in  the  median 
plane  and  the  halves  are  turned  aside. 

The  lateral  boundary  of  the  fourth  ventricle,  on  each  side, 
is  formed,  from  below  upwards,  by  the  clava,  the  upper  part 
of  the  funiculus  cuneatus,  the  restiform  body  or  inferior 
peduncle  of  the  cerebellum,  the  brachium  pontis  or  middle 
peduncle  of  the  cerebellum,  and  the  brachium  conjunctivum 
or  superior  peduncle  of  cerebellum. 

Dissection. — On  one  side  cut  through  the  brachium  conjunctivum,  the 
brachium  pontis  and  the  restiform  body,  and  so  separate  one  lateral  half  of 
the  cerebellum,  which  must  be  laid  aside  for  the  present  but  must  be  preserved 
for  future  use. 

When  the  dissection  is  completed  the  dissectors  will  be 
able  to  recognise  that  the  anterior  part  of  the  cavity  of  the 
fourth  ventricle  is  rhomboidal  in  form.  It  constitutes  the  so- 
called  rhomboidal  fossa,  which  is  surrounded  by  the  lateral 
boundaries  of  the  ventricle  and  closed  anteriorly  by  the  pons 
and  the  posterior  surface  of  the  ventral  part  of  the  upper 
portion  of  the  medulla  oblongata.      Only  the  lower  part  of  the 


FOURTH  VENTRICLE  537 

rhomboidal  fossa  lies  in  the  medulla  oblongata;  the  inter- 
mediate part  is  in  the  metencephalon,  that  is,  it  lies  anterior 
to  the  cerebellum  and  posterior  to  the  lower  part  of  the  pons ; 
and  the  upper  part  is  in  the  isthmus  rhombencephali. 

The  loiver  part  of  the  rhomboidal  fossa  is  triangular  in  out- 
line, and  its  inferior  angle  is  continuous  with  the  central  canal 
of  the  lower  part  of  the  medulla  oblongata.  The  anterior 
boundary  or  floor  of  this  part  of  the  fossa  is  marked  by  a 
number  of  converging  sulci,  and  is  called  the  calamus 
scriptorius.  Along  the  lateral  margins  of  the  lower  part  of 
the  fossa  will  be  seen  the  remains  of  the  torn  epithelial  roof 
of  the  lower  part  of  the  fourth  ventricle.  These  torn  margins 
are  the  tcenice  of  the  fourth  ventricle.  The  intermediate  part  of 
the  rhotnboidal  fossa  is  separable  into  a  lower  wider  part, 
which  is  prolonged  laterally,  on  each  side,  below  and  posterior 
to  the  restiform  body,  as  the  lateral  recess  of  the  fourth 
ventricle.  The  upper  section  of  the  intermediate  part  of 
the  fossa  is  bounded  laterally  by  the  brachia  pontis  and  is 
much  narrower  than  the  lower  part.  The  upper  part  of  the 
rhomboidal  fossa  lies  posterior  to  the  pons  and  between  the 
brachia  conjunctiva.  At  its  upper  end  it  becomes  continuous 
with  the  aquseductus  cerebri  of  the  mid-brain. 

T\^Q,  floor .^  or  anterior  boundary^  of  the  fossa  rhomboidalis  is 
the  floor,  or  anterior  boundary,  of  the  fourth  ventricle.  In 
the  upper  part  of  its  extent  it  is  formed  by  the  posterior 
surface  of  the  pons,  and  in  the  lower  part  by  the  posterior 
surface  of  the  ventral  part  of  the  upper  portion  of  the  medulla 
oblongata.  It  is  divided  into  lateral  portions  by  a  median 
sulcus  which  is  deeper  below,  in  the  region  of  the  calamus 
scriptorius,  and  shallower  above.  On  each  side  of  the  median 
sulcus  is  the  eminentia  medialis.  In  the  upper  part  of  the 
fossa  the  eminentia  medialis  occupies  practically  the  whole 
of  each  lateral  half  of  the  floor ;  in  the  upper  part  of  the 
intermediate  portion  of  the  fossa  a  nodular  eminence,  the 
colliculus facialis^  appears  on  its  surface;  below  the  colliculus 
it  narrow^s  rapidly,  and  it  terminates,  below,  in  a  pointed  tri- 
angular process  called  the  trigonmn  hypoglossi.  The  medial 
eminence  is  bounded  laterally  by  a  sulcus,  the  sulcus  limit ans. 
In  the  upper  region,  along  the  lateral  border  of  the  sulcus 
limitans,  is  a  narrow  bluish  tinted  area  called  the  locus 
cceruleus ;  the  colour  of  this  area  is  due  to  a  subjacent  col- 
lection of   pigmented    cells  which  constitute    the   substantia 


538  THE  BRAIN 

ferrughiea.  Opposite  the  colliculus  facialis  the  sulcus  limitans 
expands  into  a  shallow  fossa,  the  superior  fovea.  The  lower 
end  of  the  sulcus  limitans  terminates,  in  the  upper  part  of 
the  inferior  section  of  the  rhomboidal  fossa,  in  a  definite 
depression,  the  inferior  fovea.  To  the  lateral  side  of  the 
superior  and  inferior  fovese  and  the  intermediate  part  of  the 
sulcus  limitans  is  the  area  acustica,  which  is  prolonged  laterally 
into  the  lateral  recess  where,  in  rare  cases,  a  projection,  the 
tuberculum  acusticum,  appears  on  its  surface.  Below  the 
inferior  fovea,  between  the  trigonum  hypoglossi  medially  and 
the  area  acustica  laterally,  lies  a  depressed,  grey -coloured, 
triangular  area  called  the  ala  cinerea,  which  is  separated  from 
the  lower  part  of  the  floor,  the  area  postrema^  by  a  raised 
bundle,  the  funiculus  separans.  Immediately  above  the  in- 
ferior fovea  a  number  of  ridges,  the  medullary  sfrice  (O.T.  stricB 
acusticce),  cross  the  floor  of  the  fossa.  Laterally  they  cross 
the  restiform  body,  at  the  lateral  border  of  the  fossa,  and 
become  continuous^  with  the  cochlear  root  of  the  acustic 
nerve ;  and  medially  they  disappear  into  the  median  sulcus. 

The  roof  of  the  fourth  ventricle  is  formed,  in  the  upper  area, 
by  the  medial  parts  of  the  brachia  conjunctiva  and  the  inter- 
vening anterior  medullary  velum.  Descending  upon  the 
latter,  from  above,  is  the  frenulum  veli ;  and  issuing  from  it,  in 
the  same  region,  are  the  rootlets  of  the  trochlear  nerves. 
The  lower  part  of  the  upper  portion  of  the  roof  is  covered 
by  the  lingula  of  the  cerebellum.  The  roof  of  the  inter- 
mediate section  of  the  ventricle  is  the  white  matter  of  the 
vermis  of  the  cerebellum,  and  the  roof  of  the  lower  part  is 
epithelial  ependyma  and  the  obex. 

The  tela  chorioidea  of  the  fourth  ventricle  is  the  layer  of 
pia  mater  which  covers  and  strengthens  the  epithelial  roof  of 
the  lower  part  of  the  cavity.  Between  it  and  the  epithe- 
lium at  the  lower  end  of  the  roof,  is  a  thin  layer  of  grey 
matter,  called  the  obex.  Above,  at  the  posterior  medullary 
velum,  the  tela  becomes  continuous  with  the  pia  mater  on 
the  lower  surface  of  the  vermis  of  the  cerebellum.  Laterally 
the  tela  is  prolonged,  on  each  side,  posterior  to  the  restiform 
body,  over  the  lateral  recess,  and  it  forms  the  stronger  part 
of  the  wall  of  that  expansion.  Between  the  medial  part  of 
the  tela  chorioidea  of  the  fourth  ventricle  and  the  pia  mater 
on  the  lower  surface  of  the  vermis  of  the  cerebellum  lies  the 
cisterna  cerebello-medullaris  (O.T.  cisterna  magna). 


NUCLEUS  DENTATUS  539 

Apertures  in  the  Tela  Chorioidea  of  the  Fourth  Ventricle. — 
In  the  early  stages  of  development  the  tela  chorioidea  and 
ependyma  form  an  unbroken  layer,  but  at  a  later  period  they 
are  perforated  by  three  apertures.  One  of  the  apertures,  the 
apertura  medialis  ventriculi  quarti  (O.  T.  foramen  of  Magendie\ 
lies  immediately  above  the  obex,  at  the  lower  angle  of  the 
ventricle,  and  through  it  the  cavity  of  the  fourth  ventricle 
communicates  with  the  cerebello- medullary  portion  of  the 
subarachnoid  space.  The  other  two  apertures  lie  at  the 
apices  of  the  lateral  recesses,  immediately  posterior  to  the 
fila  of  the  glossopharyngeal  nerves. 

Chorioid  Plexuses  of  the  Fourth  Ventricle. — The  chorioid 
plexuses  are  vascular  invaginations  of  the  ependym.a  beneath 
the  tela  chorioidea.  In  the  lower  part  of  the  ventricle 
they  form  two  parallel  bands,  one  on  each  side  of  the  median 
plane,  and  their  lower  ends  project  through  the  medial  aper- 
ture. At  the  upper  part  of  the  tela  chorioidea  they  com- 
municate together,  and  then  each  passes  laterally  into  the 
corresponding  lateral  recess  and  their  lateral  extremities 
project  through  the  lateral  apertures. 

Dissection. — The  dissector  should  now  introduce  his  fingers  into  the 
great  horizontal  sulcus  of  that  half  of  the  cerebellum  which  is  still  connected 
with  the  medulla  oblongata  and  the  pons,  and  tear  the  upper  part  of  this 
side  of  the  organ  away  from  the  lower  part.  By  this  proceeding  the 
manner  in  which  the  peduncles  enter  the  white  medullary  centre,  and 
also  to  some  extent  the  general  distribution  of  their  fibres,  will  be  seen. 

AYhen  these  have  been  demonstrated  this  half  of  the  cerebellum  should  also 
be  separated  by  cutting  through  the  peduncles  at  the  points  where  they 
enter  the  central  white  matter,  A  horizontal  section  may  then  be  made 
through  the  other  half  of  the  organ,  rather  nearer  its  upper  surface  than 
its  lower  surface.     This  will  reveal  the  nucleus  dentatus. 

Nucleus  Dentatus  of  the  Cerebellum. — This  is  a  collection 
of  grey  matter,  embedded  in  the  white  medullary  centre  of 
the  lateral  hemisphere  of  the  cerebellum.  It  presents  an 
appearance  very  similar  to  a  nucleus  which  lies  in  the  olive  of 
the  medulla  oblongata.  It  is  a  thin  lamina  of  grey  matter, 
which  appears  on  section  as  a  wavy  line  folded  upon  itself, 
so  as  to  form  a  crumpled  grey  capsule  with  a  mouth  open 
towards  the  median  plane.  The  greater  number  of  the  fibres 
w^hich  build  up  the  brachium  conjunctivum  issue  from  its 
mouth. 

There  are  other  smaller  isolated  nuclei  of  grey  matter  in  the  white 
medullary   centre   of  the   cerebellum,    but    these   cannot,    as   a   rule,   be 


540 


THE  BRAIN 


demonstrated  in  a  specimen  obtained  in  the   dissecting-room.     They  lie 
nearer  the  median  plane. 

Dissection. — A  series  of  transverse  sections  should  now  be  made 
through  the  pons  and  the  medulla  oblongata,  in  order  that  something  of 
their  internal  structure  may  be  learned. 

As  a  matter  of  fact  little  of  the  structure  of  the  medulla  oblongata  can  be 
learnt  from  specimens  obtained  in  the  dissecting-room  ;  but  in  sections 
properly  prepared  and  stained  a  number  of  important  points  can  be 
seen. 

Structure  of  the  Medulla  Oblongata. — When  transverse  sections  are 
made  through  the  medulla  oblongata  at  different  levels,  a  faint  line,  called 
the  median  raphe  and  occupying  the  median  plane,  is  seen  to  divide  it 


Cuneate  nucleus 


Gracile  nucleus 


Cuneate  nucleus 

Tractus  spinalis  of  fifth 

nerve 

Substantia  gelatinosa 

Rolandi 

Cerebello-spinal 

fasciculus 

Lateral  cerebro-spinal 

fasciculus 

Detached  anterior 
column  of  grey  matter 

Decussation  of  pyramids 


Fasciculus  anterior  proprius 


Fig.  226. — Section  through  the  lower  part  of  the 
Medulla  Oblongata  of  the  Orang. 


into  two  exactly  similar  lateral  portions.  The  raphe  is  formed  by  the 
close  intersection  of  fibres  running  in  different  directions. 

Each  half  of  the  medulla  oblongata  is  composed  of  (a)  strands  of  white 
matter  ;  {b)  grey  matter,  which  is  present  both  in  the  form  of  direct  con- 
tinuations into  the  medulla  oblongata  of  portions  of  the  grey  matter  of 
the  spinal  medulla,  and  in  the  form  of  isolated  clumps,  which  are  not 
represented  in  the  spinal  medulla ;  and  (c)  the  formatio  reticularis,  a 
substance  which  is  composed  of  grey  matter  coarsely  broken  up  by  fibres 
which  traverse  it  in  different  directions.  The  white  matter,  as  in  the 
spinal  medulla,  is  disposed  for  the  most  part  on  the  surface  and  the  grey 
matter  in  the  interior,  but  in  the  open  part  of  the  medulla  oblongata  the 
grey  matter  comes  to  the  surface  on  its  dorsal  aspect,  and  forms  the 
obex  (p.  538). 

When  the  grey  matter  of  the  spinal  medulla  is  traced  up  into  the  medulla 
oblongata,  many  striking  changes  in  its  arrangement  become  apparent. 
Owing  to  the  increase  in  size  of  the  large  wedge-shaped  gracile  and  cuneate 
funiculi,  the  posterior  columns  of  grey  matter  become  pressed  laterally,  so 
that  they  soon  assume  a  position  at  right  angles  to  the  median  plane,  and 
lie  very  nearly  in  the  same  transverse  line.     At  the  same  time,  the  cuneate 


STRUCTURE  OF  MEDULLA  OBLONGATA    541 

and  gracile  nuclear  columns  of  grey  matter  which  grow  out  from  the  basal 
portion  of  the  posterior  column  and  underlie  the  strands  of  the  same  name, 


Funiculus  gracilis 

Funiculus 
cuneatus 

Tractus 
spinalis  of 
fifth  nerve     /; 

Forniatio 
reticularis 


Cerebello-     ."S 


Gracile  nucleus 


Cuneate 
nucleus 


spinal  fasci- 
culus 


Lower  end 
of  olive 


Substantia 
gelatinosa 
Rolandi 

Decussation 
of  the  lemniscus 


Medial 
—accessory 
olivarj-  nucleus 
Fila  of  the 
hypoglossal 
nerve 


Fig.  227. — Transverse  section  through  the  lower  part  of  the  Medulla 
Oblongata  of  a  full-time  Foetus  above  the  Decussation  of  the  Pyramids, 
treated  by  the  Weigert-Pal  method.  The  grey  matter  is  white,  and  the 
medullated  strands  of  nerve  fibres  are  black. 


Grey  mai  ter 
around  canal 


Central  canal 


Decussation 
of  pyram  ids 


Funiculus 

gracilis 

Funiculus 

cuneatus 

Tractus  spinalis 
of  fifth  nerve 

Substantia 
gelatinosa 
■»:\   Rolandi 


:  ^.^,,^»i_Cerebello-spinal 

"""       ^    fasciculus 


Detached  head  of 
anterior  column 
of  grey  matter 

Lateral  part  of  anterior 
funiculus  pushed  aside 
b>  decussation 


Antero-median  furrow 


Fig.  228. — Transverse  section  through  lower  end  of  the  Medulla  Oblongata  of 
a  full-time  Foetus,  treated  by  the  Weigert-Pal  method.  The  grey  matter 
is  therefore  bleached  white  ;  whilst  the  medullated  tracts  are  black. 

begin  to  make  their  appearance,     f^rom  the  deep  aspect  of  these  nuclei, 
fibres,  which  take  origin  within  them,  stream  antero-medially  through  the 


542 


THE  BRAIN 


neck  of  the  posterior  column,  so  as  to  reach  the  raphe.  The  caput 
columnae  is  in  this  way  cut  ofif  from  the  basal  portion.  The  basal  portion 
remains  in  close  relation  to  the  central  canal,  whilst  the  caput  and 
substantia  gelatinosa  (Rolando)  is  placed  close  to  the  surface,  enlarges  as  it 
is  traced  upwards,  and  forms  the  prominence  on  the  surface  which  has  been 
described  already  as  the  funiculus  and  tubercle  of  Rolando.  The  fibres 
which  have  thus  broken  up  the  neck  of  the  posterior  column,  and  which 
come  from  the  cuneate  and  gracile  nuclei,  are  termed  the  internal  arcuate 
fibres.  They  reach  the  raphe  on  the  deep  or  dorsal  aspect  of  the  pyramids, 
and,  in  the  median  plane,  they  form  a  very  complete  decussation  with  the 
corresponding  fibres  of  the  opposite  side.  This  decussation  is  termed  the 
decussation  of  the  lemniscus  or  the  sensory  decussation.  As  soon  as  they 
reach  the  opposite    side   of  the  medulla  oblongata,  the  internal  arcuate 


Gracile 
nucleus 

Cuneate 
nucleus 

Substantia 

gelatinosa 

Rolandi 

Internal 

arcuate 

fibres 

Medial 

accessory 

olivary 

nucleus 

Hypoglossal 


Funiculus 
gracilis 

Funiculus 
cuneatus 


Tractus  spinalis 
of  the  trigeminal 
nerve 


Cerebello-spinal 
fasciculus 


Hypoglossal 
nerve 


Olivary 

nucleus 


Pyramid 


Fig.  229. — Transverse  section  through  the  Medulla  Oblongata  of  new-born 
Child  at  the  level  of  the  lower  part  of  the  olive,  stained  by  the  Weigert- 
Pal  method. 


fibres  turn  upwards  and  form  a  longitudinal  tract  called  the  lemniscus. 
It  is  placed  close  to  the  raphe  and  on  the  dorsal  aspect  of  the  corresponding 
pyramid. 

The  anterior  column  of  grey  matter  shares  a  like  fate  in  the  medulla 
oblongata,  but  at  a  lower  level,  at  the  hands  of  the  fasciculus  cerebro- 
spinalis  lateralis  (O.T.  crossed  pyramidal  tract).  This  great  bundle,  in 
passing  from  the  pyramid  into  the  lateral  funiculus  of  the  opposite  side  of 
the  spinal  medulla,  traverses  the  anterior  column,  completely  breaks  up 
its  intermediate  part  and  separates  its  head  from  its  basal  portion.  The 
further  history  of  the  detached  head  need  not  be  traced,  but  it  is  well 
to  note  that  the  basal  part  of  the  anterior  column  of  grey  matter  remains 
in  position  on  the  ventral  and  lateral  aspect  of  the  central  canal. 

At  a  higher  level  the  central  canal,  surrounded  by  the  basal  portions  of 
the  two  columns  of  grey  matter,  gradually  inclines  towards  the  dorsal  aspect, 
until  it  reaches  the  surface.  The  grey  matter  which  surrounds  it  is  now 
spread  out  on  the  floor  of  the  fourth  ventricle,  and  in  such  a  manner  that 


STRUCTURE  OF  MEDULLA  OBLONGATA    543 


the  portion  which  corresponds  to  the  basal  part  of  the  anterior  column  of  the 
spinal  medulla  is  situated  close  to  the  median  plane,  whilst  the  part  which 
represents  the  base  of  the  posterior  column  occupies  a  more  lateral  position. 
Therefore  the  nucleus  of  origin  of  the  hypoglossal  nerve  is  placed  in  the 
median  part  of  the  floor,  whilst  the  nucleus  of  termination  of  the  vagus 
and  glosso-pharyngeal  nerves  lies  in  the  lateral  part  of  the  floor. 

The  most  conspicuous  of  the  isolated  clumps  of  grey  matter  in  the 
medulla  are  the  olivary  nucleus  and  the  two  accessory  olivary  nuclei.  The 
olivary  muleus  lies  subjacent  to  the  olivary  eminence,  and  is  a  very  con- 
spicuous object  in  transverse  sections  through  this  region.  In  such  sections, 
it  presents  the  appearance  of  a  thick  wavy  or  undulating  line  of  grey  matter, 
folded  upon  itself  so  as  to  enclose  a  space  filled  with  white  matter  and  open 


Lemniscus 

Medial 

accessor^' 

olivarj^ 

nucleus 


Ligula 


Tractus 
.-^  .      -  solitarius 

Vagus  nen'e 

^[edial 
longitudinal      .y 
bundle       \^ 

Hj'poglossal 
nerve 


Dorsal 
accessory 

olivary 
nucleus 


Fig.  230. — Transverse  section  through  the  Medulla  Oblongata  at 
level  of  the  mid-point  of  the  olive  (W'eigert-Pal  stain). 


towards  the  median  plane.  It  is  in  reality  a  lamina  arranged  in  a  purse- 
like manner  with  its  open  mouth  directed  towards  the  raphe. 

The  accessory  olivary  nuclei  are  two  band-like  lamince  of  grey  matter, 
which  are  placed  one  on  the  dorsal  and  one  on  the  medial  aspects  of  the 
main  nucleus. 

Posterior  to,  or  deeper  than,  the  olive  and  pyramid  is  the  forynatio 
reticularis  of  the  medulla  oblongata.  It  is  divided  into  a  lateral  and  a 
medial  field  by  the  fila  of  the  hypoglossal  nerve  as  they  traverse  the  sub- 
stance of  the  medulla  oblongata  to  reach  the  surface.  In  the  lateral  portion, 
which  lies  posterior  to  the  olive,  there  is  a  considerable  quantity  of  grey 
matter,  continuous  with  that  of  the  spinal  medulla  ;  it  is  therefore  called 
the  formatio  grisea.  In  the  medial  part,  however,  which  lies  posterior 
to  the  pyramid,  the  grey  matter  is  extremely  scanty,  and  the  reticular 
matter  here  is  termed  \hQ.  formatio  alba. 


544 


THE  BRAIN 


The  nerve  fibres  which  traverse  the  formatio  reticularis  run  both  in  the 
transverse  and  in  the  longitudinal  direction.  The  tj^mtsverse  Jibres  are  the 
internal  arcuate  fibres.  The  longitudinal  fibres  are  derived  from  different 
sources  in  the  two  fields.  In  the  lateral  part  of  the  formation  they  represent 
the  fibres  of  the  lateral  funiculus  (after  the  removal  of  the  cerebello-spinal 
and  the  lateral  cerebro- spinal  fasciculi),  which  are  continued  up  under  cover 
of  the  olive.  In  the  medial  part,  or  formatio  alba,  two  longitudinal  strands 
take  origin,  viz.,  the  lemniscus  and  the  median  longitudinal  fasciculus. 
Both  lie  close  to  the  raphe.  The  lemniscus  is  placed  immediately  posterior 
to  the  pyramid,  and  is  formed  by  the  internal  arcuate  fibres  after  their 
decussation.  The  median  longittidinal  fasciculus  takes  form  in  the  upper 
part  of  the  medulla  oblongata,  immediately  subjacent  to  the  grey  matter 


Anterior  medullary  velum 

Ventricle  iv.  ^  I 

Mesencephalic  root  of  fifth  nerve 

Medial  longitudinal  "^ 

bundle  """ 

Formatio  reticularis 

Nucleus  of 
lateral  lenmiscus    " 


Grey  matter  on  floor 

of  ventricle  iv. 
Brachium 
conjunctivum 


Trigeminal 


Lateral  lemniscus 

^  Commencing  decus- 
l  sation  of  brachium 
conjunctivum 

^  Medial  lemniscus 


Transverse 
fibres  of 
pons 


Pyramidal  bundles  (cerebro-spinal 
fasciculi) 

Fig.  231. — Transverse  section  through  the  upper  part  of  the  Pons 
of  the  Orang. 


of  the  floor  of  the  fourth  ventricle.  It  is  formed  by  longitudinal  fibres  of 
the  formatio  alba  which  come  from  the  fasciculus  anterior  proprius  of  the 
spinal  medulla. 

Internal  Structure  of  the  Pons. — When  transverse  sections  are  made 
through  the  pons,  it  is  seen  to  consist  of  two  well-defined  parts,  viz.,  a 
ventral  and  a  dorsal.  Broadly  speaking,  the  ventral  part^  pars  basalis, 
corresponds  to  the  pyramidal  parts  of  the  medulla,  and  the  basal  parts  of 
the  pedunculi  cerebri ;  whilst  the  dorsal  paH  corresponds  to  the  formatio 
reticularis  of  the  medulla  oblongata  and  the  tegmental  parts  of  the  pedunculi 
cerebri. 

The  basal  part  of  the  pons  is  the  larger  of  the  two  subdivisions.  It 
is  composed  of  a  large  number  of  transverse  bundles  of  fibres,  through 
the  midst  of  which  coarse  longitudinal  bundles  of  fibres  proceed  down- 
wards from  the  bases  of  the  pedunculi  cerebri  to  form,  in  the  medulla 
oblongata,  the  two  pyramids.  Scattered  amongst  these  transverse  and 
longitudinal  bundles  of  fibres,  and  filling  up  the  interstices  between  them. 


INTERNAL  STRUCTURE  OF  PONS  545 

there  is  a  large  amount  of  grey  matter  which  forms  the  nuclei  pontis.  Of 
the  transverse  fibres  two  distinct  sets  may  be  recognised,  viz.,  the  superficial 
transverse  fibres,  through  the  midst  of  which  the  bundles  of  cerel^ro-spinal 
fibres  are  prolonged,  and  a  deeper  set  termed  the  corpus  trapezoidiini.  The 
superficial  tra7tsverse  fibres  traverse  the  entire  thickness  of  the  ventral  part 
of  the  pons,  and  on  each  side,  pass  into  the  corresponding  brachium  pontis. 
The  trapezia  I  fibres  lie  posterior  to  the  cerebro-spinal  bundles  in  the  boundary 
area  between  the  dorsal  and  ventral  parts  of  the  pons,  but  encroaching  con- 
siderably into  the  ground  of  the  former.  They  are  seen  only  in  the  lower 
part  of  the  pons,  and  they  pass  into  the  lateral  lemniscus.  They  take  origin 
in  the  terminal  nucleus  of  the  cochlear  division  of  the  acustic  nerve. 

The  dorsal  or  tegmental  part  of  the  pons  is,  for  the  most  part,  formed 
of  a  prolongation  upwards  of  the  formatio  reticularis  of  the  medulla. 
Superiorly  it  is  carried  into  the  tegmental  parts  of  the  pedunculi  cerebri. 
It  is  divided  into  two  lateral  parts  by  a  median  raphe,  which  is  continuous 
below  with  the  raphe  of  the  medulla  oblongata  and  above  with  the  raphe  of 
the  tegmental  part  of  the  mesencephalon,  whilst  over  its  dorsal  surface  is 
spread  a  thick  layer  of  grey  matter  which  belongs  to  the  upper  part  of  the 
floor  of  the  fourth  ventricle.  In  transverse  sections  through  the  pons  a 
dark  spot  in  the  lateral  part  of  the  floor  indicates  the  position  of  a  small 
mass  of  pigmented  cells  called  the  substantia  ferruginea.  It  underlies 
the  locus  coeruleus. 

Four  strands  of  longitudinal  fibres  are  seen  on  each  side  in  transverse 
sections  through  the  dorsal  part  of  the  pons.  These  are  (i)  the  medial 
lemniscus,  (2)  the  lateral  lemniscus,  (3)  the  medial  longitudinal  bundle,  and 
(4)  the  brachium  conjunctivum. 

The  medial  lemniscus  assumes  in  the  pons  a  ribbon-shaped  form.  It  is 
placed  between  the  ventral  part  of  the  pons  and  the  formatio  reticularis 
of  the  dorsal  part. 

The  lateral  levinisciis,  largely  composed  of  fibres  derived  directly  or  in- 
directly from  the  corpus  trapezoidum,  is  seen  in  the  upper  part  of  the  pons. 
It  sweeps  round  the  lateral  side  of  the  brachium  conjunctivum  to  gain  the 
surface. 

The  medial  longitudinal  bundle  is  much  more  distinct  than  it  is  lower 
down  in  the  medulla  oblongata.  It  has  separated  itself  more  completely 
from  the  longitudinal  fibres  of  the  formatio  reticularis,  and  it  is  now  seen, 
close  to  the  median  plane,  immediately  subjacent  to  the  grey  matter  of 
the  floor  of  the  fourth  ventricle. 

The  brachium  conjunctivum,  in  transverse  sections,  presents  a  semi- 
lunar outline.  It  occupies  a  lateral  position  in  the  dorsal  part  of  the 
pons,  and  gradually  sinks  deeply  into  its  substance,  although  it  does  not 
become  completely  submerged  until  it  reaches  the  mesencephalon. 

The  stiperior  olive  is  a  small  isolated  clump  of  grey  matter  which 
is  embedded  in  the  dorsal  part  of  the  pons  in  the  path  of  the  corpus 
trapezoidum. 


VOL.  II — 35 


546  THE  AUDITORY   APPARATUS 


THE  AUDITORY  APPARATUS, 

The  Organ  of  hearing  admits  of  a  very  natural  subdivision 
into  three  parts,  viz.,  the  externa],  the  middle,  and  the 
internal  ear.  The  external  ear  consists  of  the  auricle  and 
the  external  acustic  meatus.  The  auricle  collects  the  waves 
of  sound,  and  is,  comparatively  speaking,  of  subsidiary  im- 
portance in  man,  although  it  is  highly  developed  and  of 
considerable  service  in  some  of  the  lower  animals.  The 
external  acustic  meatus  is  a  passage  leading  inwards  from 
the  bottom  of  the  concha  to  the  membrana  tympani,  which 
separates  the  external  from  the  middle  ear.  The  middle  ear 
is  a  narrow  chamber  termed  the  tympanic  cavity.  It  is  inter- 
posed between  the  external  acustic  passage  and  the  internal 
ear  or  labyrinth,  and  the  main  part  of  its  lateral  wall  is  formed 
by  the  membrana  tympani.  Stretching  across  the  cavity  of 
the  tympanum,  from  its  lateral  to  its  medial  wall,  there  is  a 
chain  of  three  small  bones,  called  the  auditory  ossicles.  The 
internal  ear  or  labyrinth  is  a  most  essential  part  of  the  organ. 
It  consists  of  a  complicated  system  of  cavities  situated  in  the 
densest  part  of  the  petrous  portion  of  the  temporal  bone.  These 
cavities  contain  fluid  called  perilymph,  and  also  a  membranous 
counterpart  of  the  bony  chambers,  called  the  membranous 
labyrinth.      Within  the  latter  there  is  fluid  termed  endolymph. 

Dissection. — The  dissection  of  the  ear  should  be  conducted  differently 
on  opposite  sides. 

On  one  side  remove  the  lateral  pterygoid  lamina  and  the  remains  of  the 
external  and  internal  pterygoid  muscles,  if  that  has  not  been  done  already. 
Then  clear  away  the  tensor  palati  muscle  and  expose  the  lateral  surface  of 
the  auditory  tube.  Dissect  on  the  postero-medial  aspect  of  the  tube  and 
expose  the  levator  palati  muscle  from  the  lateral  side.  Follow  the  muscle 
downwards  and  medially,  below  the  lower  orifice  of  the  tube,  into  the 
soft  palate.  Then  detach  the  auditory  tube  from  the  posterior  border 
of  the  medial  pterygoid  lamina ;  cut  the  levator  palati,  at  the  point 
where  it  enters  the  soft  palate,  and  separate  the  cartilaginous  part  of  the 
auditory  tube  from  any  parts  of  the  wall  of  the  pharynx  which  may  still  be 
connected  with  it.  When  this  has  been  done  turn  to  the  temporal  bone  ; 
place  the  saw  at  right  angles  to  the  external  surface  of  the  squamous  part 
and  saw  through  the  bone,  along  the  line  of  the  petro-tympanic  fissure,  to  the 
posterior  border  of  the  spine  of  the  sphenoid.  Turn  next  to  the  medial 
surface  and  saw  through  the  body  of  the  siDhenoid  at  the  level  of  the  anterior 
boundary  of  the  foramen  lacerum  ;  then,  with  the  aid  of  the  chisel  and  bone 
forceps,  detach  the  posterior  border  of  the  great  wing  of  the  sphenoid  from 


EXTERNAL  MEATUS 


547 


the  anterior  angle  of  the  petrous  part  of  the  temporal  bone.  When  the 
dissection  is  properly  done  the  greater  part  of  the  temporal  bone  is  removed 
from  the  remainder  of  the  skidl,  with  the  cartilaginous  part  of  the  auditory 
tube  attached  to  the  anterior  angle  of  its  petrous  portion,  and  a  small  part 
of  the  body  of  the  sphenoid  bone  attached  to  its  apex.  The  anterior  \vall 
of  the  mandibular  fossa  was  separated  by  the  first  saw  cut,  and  the  posterior 
wall  is  exposed,  with  the  cartilaginous  part  of  the  auditory  tube  attached  to 
its  medial  end  and  the  cartilaginous  part  of  the  external  acustic  meatus  to 
its  lateral  border.  The  dissector  should  now  cut  away  the  tragus  of  the 
auricle,  to  expose  the  orifice  of  the  external  meatus  which  lies  at  the  bottom 
of  the  concha  ;    then,  with  knife  or  scissors,  he  must  remove  the  anterior 


Tympanic  antrum        Canalis  facialis 


Pyramid 

Apertura 

tympanica 

canaliculi 

chordae 

Groove  for 

membrana 

tympani 


Canal  for  tympanic  nerve 


Fig.  232.  — Frontal  section  of  the  Right  Temporal  Bone  passing  through  the 
external  and  the  internal  acustic  meatuses. 

wall  of  the  cartilaginous  part  of  the  external  meatus.  Next  pass  a  probe 
into  the  bony  part  of  the  meatus  to  gauge  its  length,  and,  whilst  the  probe 
is  kept  in  position  as  a  guide,  cut  away  the  anterior  wall  of  the  bony 
part  of  the  meatus,  taking  care  not  to  injure  the  tympanic  membrane  which 
closes  the  medial  end  of  the  meatus.  \Yhen  the  dissection  is  completed  the 
boundaries  of  the  meatus  and  the  outer  surface  of  the  tympanic  membrane 
should  be  examined. 

Meatus  Acusticus  Externus. — The  external  acustic  meatus 
runs  anteriorly  and  medially  from  its  lateral  orifice  to  its 
medial  boundary,  and,  during  its  course,  it  forms  a  slight  curve 
with  the  convexity  upwards.  Its  total  length,  measured  from 
the  bottom  of  the  concha  to  the  tympanic  membrane,  is  about 


548 


THE  AUDITORY  APPARATUS 


24  mm.,  of  which  8  mm.  corresponds  with  the  cartilaginous, 
and  16  mm.,  with  the  bony  part  of  the  canal;  but,  as  the 
membrana  tympani  is  placed  obliquely,  the  anterior  wall  and 
the  floor  are  longer  than  the  posterior  wall  and  the  roof, 
respectively.  Moreover,  the  diameter  of  the  canal  is  not 
uniform.  It  is  narrowest  at  the  isthmus,  which  lies  about 
5  mm.  from  the  tympanic  membrane  ;  and  its  vertical  diameter 
is  greatest  at  the  lateral  end,  whilst  its  antero-posterior 
diameter  is  greatest  at  its  medial  end.  These  facts  must 
be  borne  in  mind  during  the  removal  of  foreign  bodies  which 
have  made  their  way  into  the  canal.     As  the  tube  passes  from 


Osseous  part  of  meatus 


Recessus 
epitympanicus 
Malleus- 
Cochlea. 
Tympanum. 
Membrana 
tympani 


Internal  carotid 
artery' 


,Crus  antihelicis 
inferior 

Cymba  conchae 
Crus  helicis 


Cartilaginous 
part  of  meatus 
Cavum  conchae 


Lower  boundary 
of  incisura 
intertragica 


Fig.  233.— Vertical  transverse  section  through  the  Right  Ear  :  anterior  half 
of  section  viewed  from  behind.      (Howden.) 


the  surface  medially  it  describes  a  gentle  sigmoid  curve,  but 
its  general  direction  is  towards  the  median  plane  with  a 
slight  inclination  anteriorly.  The  skin  lining  the  cartilaginous 
portion  is  abundantly  furnished  with  ceruminous  glands  and 
is  provided  also  with  laterally  directed  hairs,  which  tend  to 
prevent  the  entrance  of  dust.  The  cutaneous  lining  of  the 
osseous  part,  which  is  thin  and  tightly  adherent  to  the 
subjacent  periosteum,  is  destitute  of  hairs,  and  glands  are  for 
the  most  part  absent.  The  cutaneous  lining  of  the  meatus  is 
continued  in  the  form  of  an  exceedingly  delicate  layer  over 
the  outer  surface  of  the  membrana  tympani. 


MEMBRANA  TYMPANI  549 

When  the  direction,  the  length,  and  the  diameters  of  the 
external  meatus  have  been  noted,  the  dissectors  should 
examine  the  lateral  surface  of  the  tympanic  membrane. 

Membrana  Tympani. — The  slope  of  the  tympanic  mem- 
brane has  already  been  referred  to.  It  slopes  very  obHquely 
downwards,  anteriorly  and  medially,  and  it  is  deeply  concave 
externally.  The  deepest  point  of  the  concavity  is  the  umbo^ 
which  corresponds  with  the  lower  end  of  a  bar  of  bone,  the 
handle  of  the  malleus^  which  is  embedded  in  the  membrane 
and  can  be  seen  through  the  thin  layer  of  tissue  covering 
it.  The  handle  of  the  malleus  extends  upwards,  and 
slightly  posteriorly,  from  the  umbo  towards  the  roof  of  the 
meatus ;  and  a  short  distance  from  the  upper  margin  of 
the  membrane  it  becomes  continuous  with  a  small  laterally 
directed  process,  the  lateral  process  of  the  malleus,  which  bulges 
the  membrane  towards  the  meatus.  Above  the  lateral  process 
of  the  malleus  is  a  portion  of  the  membrane  which  is  less 
tense  than  the  remainder.  This  is  the  membrana  flaccida 
(Shrapnell's  membrane).  It  is  bounded  anteriorly  and 
posteriorly  by  relatively  thickened  folds,  the  anterior  and 
posterior  tynipano-malleolar  folds.  The  whole  of  the  peripheral 
margin  of  the  membrane,  except  that  which  corresponds 
with  the  membrana  flaccida,  is  lodged  in  a  ring-like  sulcus 
of  bone,  the  annulus  tynipaniais,  which  is  formed  by  the 
tympanic  element  of  the  temporal  bone. 

Dissection. — After  the  examination  of  the  external  meatus  is  completed 
the  dissector  must  secure  the  tensor  tympani  muscle,  which  springs  from  the 
anterior  aspect  of  the  petrous  part  of  the  temporal  bone,  close  to  the  apex 
and  above  the  level  of  the  cartilaginous  part  of  the  auditory  tube.  Having 
secured  it,  he  must  trace  it  laterally,  above  the  auditory  tube,  to  the  point 
where  it  passes  into  the  bony  canal  through  which  it  enters  the  tympanum. 
Then  he  must  cut  away  the  antero-lateral  wall  of  the  cartilaginous  part  of 
the  auditory  tube,  from  the  pharyngeal  orifice  to  the  upper  extremity,  and 
pass  a  probe  through  the  bony  part  of  the  tube  into  the  tympanum.  He 
should  next  turn  to  the  anterior  surface  of  the  petrous  part  of  the  temporal 
bone  and,  with  chisel  and  bone  forceps,  carefully  remove  the  tegmen 
tympani  and  expose  the  tympanic  cavity  from  above.  The  dissection  must 
be  carried  anteriorly  into  the  auditor^'  tube  and  posteriorly  into  the  tympanic 
antrum.  As  the  dissection  is  carried  anteriorly  a  narrow  margin  of  bone 
must  be  left  along  the  anterior  border  of  the  tympanic  membrane,  and  care 
must  be  taken  to  avoid  injury  to  the  tendon  of  the  tensor  tympani,  which 
emerges  from  the  extremity  of  its  bony  canal,  near  the  medial  wall  of  the 
tympanum,  and  crosses  the  cavity  to  be  inserted  into  the  malleus.  The 
chorda  tympani  nerve,  which  passes  anteriorly,  close  to  the  tympanic 
membrane  and  above  the  tendon  of  the  tensor  tympani,  must  also  be 
preserved  if  possible. 


550 


THE  AUDITORY  APPARATUS 


Tympanic  Cavity  or  Middle  Ear. — The  tympanic  cavity 
is  a  small  chamber,  filled  with  air,  which  is  placed  between 
the  bottom  of  the  meatus  externus  and  the  internal  ear  or 
labyrinth.  Posteriorly  it  communicates,  by  a  relatively  large 
orifice,  with  the  tympanic  antrum  and  mastoid  air-cells ; 
whilst  anteriorly  the  auditory  tube  opens  into  it  and  puts  it 
into  connection  with  the  cavity  of  the  pharynx.  It  con- 
tains the  chain  of  auditory  ossicles  which  crosses  from  its 
lateral  to  its  medial  wall,  and  it  is  lined  with  delicate  mucous 
membrane. 

The  vertical  depth  and  the  antero-posterior  length  of  the 
tympanic   cavity   are   each   about   half  an   inch  (12.5   mm.). 

Its  width,  from  side  to  side,  is  about 
a  sixth  of  an  inch  (4.5  mm.);  and, 
as  both  its  lateral  and  medial  walls 
bulge  into  the  cavity,  its  width  in 
the  centre  is  still  further  reduced. 
The  tympanic  cavity  consists  of  (i) 
an  upper  part,  which  extends  up- 
wards beyond  the  level  of  the  mem- 
brana  tympani,  and  to  which  the 
term  recessus  epitympanicus  is  ap- 
plied; and  (2)  the  tympanum  proper^ 
which  lies  immediately  to  the  inner 
side  of  the  membrana  tympani. 
The  tympanic  cavity  presents  for 
examination  a  roof  and  a  floor, 
with  four  walls,  viz.,  anterior,  pos- 
terior, lateral,  and  medial. 
The  roof  is  composed  of  a  thin  plate  of  bone  termed  the 
legmen  tympani.  This  separates  it  from  the  middle  fossa 
of  the  cranium.  In  chronic  inflammatory  conditions  of  the 
middle  ear,  an  extension  of  the  inflammatory  process  to  the 
meninges  of  the  brain  is  always  to  be  feared. 

T\iQ.  floor  ox  jugular  wall  is  narrow,  and  is  also  formed  by 
a  thin  osseous  lamina,  which  is  interposed  between  the 
tympanum  and  the  jugular  fossa.  It  separates  the  tympanum 
from  the  bulb  of  the  internal  jugular  vein,  and  an  exten- 
sion of  an  inflammatory  condition  of  the  middle  ear,  through 
the  bone  to  the  vein,  may  lead  to  thrombosis. 

The  posterior  or  mastoid  wall  presents,  in  its  upper  part, 
the   opening   or   aditus    which    leads   from   the  recessus  epi- 


FlG.  234. — Schematic  vertical 
section  through  the  Tym- 
panum.    (From  Testut. ) 

1.  External  meatus. 

2.  Tympanic  cavity  (the  upper 

"2"  is  in  the  recessus  epi- 
tympanicus). 

3.  Promontory  on  medial  wall. 

4.  Membrana  tympani. 


TYMPANIC  CAVITY 


55-^ 


tympanicus  into  the  tympanic  antrum,  and  below  this,  close 
to  the  medial  wall,  is  a  small  hollow  conical  projection  termed 
tke  pyra7md.  This  is  perforated,  on  its  summit,  and  the 
aperture  leads  into  a  canal  which  curves  posteriorly  and  then 
downwards  until  it  opens  into  the  lower  part  of  the  last 
stage  of  the  canalis  facialis.  The  curved  canal  of  the  pyramid 
lodges  the  stapedius  muscle,  the  delicate  tendon  of  which 
enters  the  tympanic  cavity  through  the  aperture  on  the 
summit  of  the  pyramid.     Lateral  to  the  pyramid  is  the  aper- 


Recessus  epitympanicus 


Fossa 
incudis 

Apertura 

ti^mpanica 

canaliculi 

chordae 


Membrana 
flaccida 

Anterior  and  pos- 
terior tympano- 
malleolar  folds 
Tendon  of  tensor 
tympani  (cut) 
Handle  of 
malleus 

Membrana 
tympani 

Tympanic  sulcus 


^d'^    \ 


Fig.  235. — Left  Membrana  Tympani  and  Recessus  Epitympanicus  viewed 
from  within.  The  neck  and  head  of  the  malleus  have  been  removed  to 
show  the  membrana  flaccida.      (Howden. ) 

ture  on  the  po&terior  wall  called  the  apertura  tympanica  cana- 
liculi chordce  through  which  the  chorda  tympani  nerve  enters 
the  tympanum. 

The  afiferior  wall  is  narrow,  because  the  medial  and  lateral 
walls  converge  anteriorly.  The  upper  part  of  this  wall  is 
occupied  by  the  opening  of  the  tensor  tympani  canal ;  the 
intermediate  part  by  the  tympanic  orifice  of  the  auditory  tube ; 
and  the  lowest  part  is  a  lamina  of  bone  which  separates  the 
tympanic  cavity  from  the  carotid  canal.  The  tympanic  end 
of  the  septum  between  the  auditory  tube  and  the  tensor 
tympani  canal,  the  processus  cochleariformis,  serves  as  a  pulley 


552 


THE  AUDITORY  APPARATUS 


round  which  the  tendon  of  the  muscle  turns  abruptly,  in  a 
lateral  direction,  towards  the  malleus. 

The  medial  zvall,  which  intervenes  between  the  tympanum 
and  the  labyrinth,  presents  certain  important  points  for  study. 
The  greater  part  of  this  wall  bulges  laterally,  into  the  cavity, 
in  the  form  of  a  very  evident  elevation  termed  the  promontory. 
Above  the  posterior  part  of  the  promontory  there  is  an  oval 
foramen,  the  fenestra  vestibuli.  Its  long  axis  is  directed 
antero-posteriorly,   and  it   opens   into   the   vestibular   part  of 


Recessus 
epitympanicus 

Body  of  incus 

Short  crus 
of  incus 

Ligament 

of  incus  J    '•'^c- 

Chorda  tym-      ,/  H^^j 
pani  nerve~y~y©3^J7 

Pyramid  ^   '^<f%.f 
Foot  of  stapes 


Superior  ligament  of  malleus 
Head  of  malleus 


Anterior  ligament 
of  malleus 


Handle  of  malleus 


Tensor  tympani 

Processus 
cochleariformis 
Osseous  part  of 
the  auditory 


«>i'  i«.        -I  ,4    at3^,    !-'•<-,-  (fi-'iFN,  Vi' 


Fig.  236. — Left  Membrana  Tympani  and  Chain  of  Tympanic  Ossicles 
seen  from  the  inner  aspect.      (Howden.) 

the  labyrinth  in  the  macerated  bone,  but  is  closed  in  the 
recent  state  by  the  footpiece  of  the  stapes,  the  most  medial 
of  the  auditory  ossicles.  The  pyramid,  on  the  posterior  wall, 
is  immediately  posterior  to  the  fenestra  vestibuli.  Above  the 
fenestra  vestibuli,  in  the  angle  formed  by  the  meeting  of 
the  roof  and  medial  wall  of  the  tympanum,  and  there- 
fore in  the  recessus  epitympanicus,  is  an  antero -posterior 
ridge.  This  is  produced  by  the  canalis  facialis  bulging  into 
the  tympanum.  The  wall  of  the  canal  is  very  thin,  and 
allows  the  white  colour  of  the  facial  nerve,  which  is  contained 
within  the  canal,  to  be  readily  seen.  Below  the  posterior 
end  of   the   promontory  is   the  fenestra  cochlecB,  an  aperture 


MEMBRANA  TYMPANI 


553 


which,  in  the  macerated  bone,  leads  into  the  cavity  of  the 
cochlea,  but,  in  the  recent  state,  it  is  closed  by  a  membrane 
which  is  stretched  across  it,  and  receives  the  name  of  the 
secondary  jjiembrajie  of  the  ty?7ipanum. 

The  lateral  wall  of  the  tympanic  cavity  is  formed  by  the 
membrana  tympani  and  the  squamous  part  of  the  temporal  bone. 

Membrana  Tsrmpani. — The  membrana  tympani  is  an 
elliptical  disc  of  membrane  which  is  stretched  across  the 
medial  end  of  the  meatus  acusticus  externus,  and  it  forms  the 
greater  part  of  the  lateral  wall  of  the  tympanum.  It  is  placed 
very  obliquely  ;  its  lower  and  its  anterior  borders  both  inclining 
medially. 


Membrana  flaccida 

Anterior  tympano 

malleolar  fold 


Handle  of  malleus. 

Antero-superior 
quadrant' 


Antero-inferior  quadran 


Posterior  tympano- 
malleolar  fold 
Lateral  process 
of  malleus 
Long  crus  of  incus 

Postero-superior 
quadrant 

Postero-inferior 
quadrant 

Cone  of  light 


Fig.  237. — Left  Tympanic  Membrane  as  viewed  from  the  external  meatus 
during  an  otoscopic  examination.  The  dotted  lines  indicate  the  manner 
in  which  the  tympanic  membrane  is  subdivided  arbitrarily  into  four  areas 
or  quadrants.      (Howden.) 


Its  mode  of  attachment  deserves  some  attention.  At  the 
medial  end  of  the  meatus  a  ring-like  ridge  of  bone,  very 
distinctly  grooved,  forms,  as  it  were,  a  frame  in  which  the 
membrane  is  set.  But  this  ridge  is  deficient  above,  where 
the  extremities  of  the  bony  ridge  are  separated  by  a  deep 
notch  (the  notch  of  Rivinus).  This  notch  is  occupied  by  a 
portion  of  the  membrane  which  is  not  so  dense  in  its  texture 
(seeing  that  the  fibrous  layer  is  absent),  and  not  so  tightly 
stretched  as  the  remainder  ;  consequently  it  receives  the  name 
of  the  membrana  flaccida  (Shrapnell's  membrane).  The  edge 
of  that  part  of  the  membrane  which  is  fixed  in  the  circular 
bony  groove,  sulcus  tympanicus,  is  thickened,  and  at  the  notch 
of  Rivinus  it  is  carried  down,  anterior  and  posterior  to  the 


554 


THE  AUDITORY  APPARATUS 


membrana  flaccida,  in  the  form  of  two  bands,  called  respec- 
tively the  anterior  and  posterior  ty7npano-77ialleoIar  folds. 

The  membrana  tympani  is  composed  of  three  layers — viz., 
an  external  cuticular  layer,  an  intermediate  fibrous  lamina, 
and  an  internal  mucous  layer.  The  handle  of  the  malleus  is 
intimately  connected  with  the  fibrous  layer,  and  is  covered 
medially  by  the  mucous  layer.  It  draws  the  membrane 
towards  the  tympanic  cavity,  and  is  the  cause  of  the  concavity 
on  the  outer  surface.     The  deepest  point  of  this  concavity 

Tympanic  antrum 
Recessus  epitympanicus 

Canalis  facialis 
Tegmen  tympani 


Fenestra  vestibuli 

Canal  for 
tensor  tympani^ 

Processus 
cochleariformis 

Promontory 


Auditory  tube 

Foramen  for 
tympanic  nerve' 


Pyramid 


Fenestra  cochleas 


Course  of  canalis  facialis 


Fig.  238. — Vertical  section  through  the  Left  Ear  :   postero-medial  half 
of  section  viewed  from  the  front,      (Howden. ) 


corresponds  with   the   flattened    extremity  of   the  handle  of 
the  malleus,  and  is  termed  the  umbo. 

In  examining  the  living  ear,  v^^ith  a  speculum,  the  surface  of  the  mem- 
brane appears  highly  polished,  and  a  cone  of  light  extends  downwards 
and  forwards  from  the  tip  of  the  handle  of  the  malleus.  A  pair  of  striae 
(Prussak's  striae),  which  correspond  to  the  anterior  and  posterior  tympano- 
malleolar  folds,  extend  from  the  processus  lateralis  of  the  malleus  to  the 
margins  of  the  notch  of  Rivinus,  and  thus  map  out  the  membrana  flaccida. 
The  long  crus  of  the  incus  can  be  faintly  seen  through  the  membrana 
tympani,  parallel  with  and  posterior  to  the  handle  of  the  malleus. 

Antrum  Tympanicum. — The  tympanic  antrum  is  a  recess 
or  air-chamber,  in  the  petrous  part  of  the  temporal  bone,  with  a 


AUDITORY  OSSICLES 


555 


diameter  of  about  one-third  of  an  inch.  It  is  placed  posterior 
to  the  tympanum,  and  communicates  by  a  relatively  large 
opening,  the  aditus,  with  the  upper  part  of  that  cavity.  It 
lies  at  a  depth  of  about  half  an  inch  from  the  surface  of  the 
skull  in  the  adult,  but  in  the  child  it  is  placed  much  more 
superficially.  It  is  lined  with  mucous  membrane,  which  is 
continuous  with  the  lining  membrane  of  the  tympanum.  The 
mastoid  portion  of  the  temporal  bone  also  is  occupied  by  air- 
spaces, the  air-ceils,  which  may 
extend  downwards  into  the  mas- 
toid process.  They  are  continu- 
ous with  one  another  and  with 
the  tympanic  antrum,  and  are 
lined  by  a  continuation  of  the 
same  mucous  membrane. 

Tympanic  Mucous  Membrane. 
— The  tympanum  is  lined 
throughout  with  a  thin  mucous 
membrane  which  is  continuous 
with  the  mucous  membrane  of 
the  pharynx.  As  already  men- 
tioned, it  forms  the  innermost 
layer  of  the  membrana  tympani,    Fig.  239. — Left  Malleus  and  incus. 

(After  Helmholtz. ) 

1.  Tendon  of  tensor  tympani. 

2.  Handle  of  the  malleus. 

3.  Long  crus  of  the  incus. 

4.  Short  crus  of  the  incus. 
6.  Anterior  process  of  the  malleus.     The 

straight  line  a  b  c  connects  the  ex- 
tremities of  the  two  crura  of  the 
incus  with  the  extremity'  of  the 
manubrium  of  the  malleus. 


and  it  is  prolonged  posteriorly 
into  the  tympanic  antrum  and 
mastoid  air-cells.  It  covers  the 
ossicles  also,  and  it  invests  the 
tendons  of  the  stapedius  and 
tensor  tympani  muscles. 

Ossicula  Auditus. — The  audi- 
tory ossicles  are  the  malleus,  the  incus,  and  the  stapes. 

The  7naileus  presents  a  head,  a  neck,  a  manubrium,  and 
two  processes  termed  the  processus  lateralis  and  the  pro- 
cessus anterior.  The  head  is  large  and  rounded.  It  is 
directed  upwards,  and  lies  above  the  level  of  the  mem- 
brana tympani,  in  the  recessus  epitympanicus,  close  to  the 
roof  of  the  tympanum.  On  its  posterior  aspect  there  is 
a  notch-like  articular  surface,  for  articulation  with  the  body 
of  the  incus.  The  77ianubriu77i  is  attached  to  the  fibrous 
layer  of  the  membrana  tympani.  The  p'ocessus  iateraiis  (O.T. 
brevis)  is  a  stunted  projection  which  springs  from  the  root  of 
the  manubrium.     It  is  directed  laterally,  and  abuts  against  the 


556 


THE  AUDITORY  APPARATUS 


membrana  tympani  immediately  below  the  membrana  flaccida. 
The  processus  anterior  (O.T.  gracilis)  is  a  slender  spicule  of 
bone  which  passes  anteriorly  into  the  petro-tympanic  fissure. 
It  almost  invariably  breaks  in  detaching  the  malleus  from  the 


Head 


Neck 


Facet  for 
incus 


Facet  for    Head 

incus  Processus 

anterior 


Processus 
lateralis 

Manubrium 
A 


Manubrium 

B 


Fig.  240. — The  Left  Malleus.      (Howden. ) 
A.   Posterior  aspect.  B.  Medial  aspect. 

adult  skull,  but  it  can  be  easily  preserved  in  the  skull  of  an 
infant. 

The  incus  is  shaped  somewhat  like  a  prsemdlar  tooth  in 


Articular  surface  for 
head  of  malleus 


Body 


Crus  breve 


Crus. 
longum 

Processus 
lenticularis 


Fig.  241. — The  Left  Incus.      (Howden.) 
A.  Anterior  aspect.  B.  Medial  aspect. 


which  the  roots  are  very  divergent.  It  presents  a  body  and 
a  long  and  a  short  crus.  The  body  is  provided  with  an 
articular  surface,  which  looks  anteriorly  and  articulates  with 
the  head  of  the  malleus.    The  short  crus  is  directed  posteriorly. 


AUDITORY  OSSICLES  557 

and  its  extremity  is  attached,  by  ligaments,  to  the  posterior  wall 
of  the  tympanum,  near  the  opening  into  the  tympanic  antrum. 
The  long  cms  proceeds  downwards  and  medially,  in  a  direction 
nearly  parallel  to  that  of  the  manubrium  of  the  malleus,  but 
more  medial,  and  on  a  plane  posterior  to  that  process.  On 
its  inferior  extremity,  which  is  bent  medially,  there  is  a  small 
knob  of  bone  called  the  processus  lenticularis.  This  articulates 
with  the  head  of  the  stapes. 

The  malleus  and  incus  move  together  on  an  axis  which  is  formed  by 
the  processus  anterior  of  the  malleus  and  the  crus  breve  of  the  incus. 
The  articular  surfaces  of  the  two  bones  are  provided  with  peculiar  catch- 
teeth  which  interlock  when  the  bones  are  performing  their  ordinary 
movements.  When,  however,  force  is  applied  to  the  inner  surface  of 
the  membrana  tympani,  as,  for  instance,  when  the  tympanum  is  inflated 
through  the  auditory  tube,  the  incudo  -  malleolar  joint  gapes  and  the 
malleus  moves  by  itself  Traction  upon  the 
attachments  of  the  stapes,  through  the  incus,  is  ^ — -Head 

thus  avoided.  />^:i:\      N^^k 

-Cms  anterior 


The  stapes  is  shaped  like  a  stirrup,     j^^p^'"' p"'''"^'' 
and  presents  a  head  or  lateral  extremity    ^^^^^Foot-piate 
separated  by  a  slightly  constricted  neck 
from   two    crura    which    join   a   medial 
plate,  the  basis  stapedis.     The  head  is    ^'^-  ^f^^^f-  f^^^^' 

11  -1  r  1  (Howden. ) 

excavated   by  an  articular   cup   for   the 

processus  lenticularis  of  the  incus.  The  crura  are  grooved 
longitudinally  on  their  concave  sides  (sulcus  stapedis).  The 
posterior  crus  is  more  sharply  curved  than. the  anterior  crus. 
The  base  fits  into  the  fenestra  vestibuli  and  corresponds  in 
its  outhne  with  that  aperture.  Its  lower  border  is  straight, 
whilst  its  upper  border  is  curved. 

Ligaments  of  the  Auditory  Ossicles. — In  addition  to  the 
delicate  capsular  ligaments,  w^hich  surround  the  joints  between 
the  auditory  ossicles,  there  are  certain  bands  which  connect 
the  bones  to  the  w^alls  of  the  tympanum  and  serve  to  restrain 
their  movements. 

In  connection  with  the  malleus  there  are  (i)  an  anterior  ligament  which 
passes  from  its  anterior  part,  at  the  root  of  the  processus  anterior,  to  the 
anterior  wall  of  the  tympanum  in  the  neighbourhood  of  the  petro-tympanic 
fissure  ;  (2)  a  latei-al  ligarnent  which  extends  from  its  lateral  process  to 
the  margin  of  the  notch  of  Rivinus  ;  and  (3)  a  superior  ligament  which 
connects  the  head  with  the  roof  of  the  tympanum. 

The  ligament  of  the  inais  binds  the  extremity  of  its  short  crus  to  the 
posterior  wall  of  the  tympanum,  whilst  the  anmilar  ligament  of  the  stapes 
connects  the  margin  of  its  base  to  the  circumference  of  the  fenestra  vestibuli. 


558 


THE  AUDITORY  APPARATUS 


Tympanic  Muscles. — These  are  two  in  number,  viz.,  the 
stapedius  and  the  tensor  tympani. 

The  stapedius  occupies  the  interior  of  the  pyramid  and  the 
canal  which  curves  downwards  from  it.  The  delicate  tendon 
of  the  stapedius  enters  the  tympanum,  through  the  aperture 
on  the  summit  of  the  pyramid,  and  is  inserted  into  the 
posterior  aspect  of  the  neck  of  the  stapes.  It  is  supphed  by 
a  branch  from  X^^  facial  nerve. 


Membrana  tympani 

Epitympanic  recess  i 

Malleus 


Cochlea 
Internal  meatus 


Internal  carotid 
Osseous  part  of  auditory  tube 
Base  of  spine  of  sphenoid 


Cartilaginous  part  of 

auiitory  tube 

Otic  ganglion 

Nerve  to  internal  pterygoid 

Levator  veli  palatini 

Lateral  recess  of  pharynx 

Cartilage  of  auditory  tube 

Middle  concha 
Anterior  lip  of  auditory  tube 

Tensor  veli  palatini 

Inferior  concha 

Hamulus 


Palat 


Gum 


Auricle 


— [External  meatus 
-  --;  Tympanic  plate 


■X'^f"  '^  Condyle  of  mandible 

Middle  meningeal  artery 

~j-  Mandibular  nerve 
—L-   External  pterygoid 
'  .     Cavity  of  auditory  tube 

.    Internal  maxillary  artery 

Internal  pterygoid 

Ramus  of  mandible 


Masseter 


..  .Buccinator 


Fig.  243. — Oblique  section  of  a  part  of  the  Head  showing  the  relation 
of  the  Auditory  Tube. 

The  tensor  tympa?ii  arises  from  the  upper  part  of  the 
cartilage  of  the  auditory  tube  and  from  the  contiguous  parts 
of  the  great  wing  of  the  sphenoid  and  the  petrous  part 
of  the  temporal  bone.  From  its  origin  it  passes  postero- 
laterally,  upon  the  processus  cochleariformis  and  above  the 
osseous  part  of  the  auditory  tube.  In  the  tympanic  cavity 
the  tendon  turns  at  right  angles,  round  the  extremity  of  the 
processus  cochleariformis,  and  passes  laterally,  towards  the 
lateral  wall  of  the  tympanum,  to  its  insertion  into  the  upper 


AUDITORY  TUBE 


559 


part  of  the  medial  surface  of  the  manubrium  of  the  malleus. 
The  tensor  tympani  receives  its  nerve  of  supply  from  the  otic 
gafigUon. 

Chorda  Tympani  Nerve. — The  chorda  tympani,  which 
traverses  the  tympanic  cavity  in  close  relation  to  the  upper 
part  of  the  membrana  tympani,  is  described  on  p.  546. 

Tympanic  Plexus. — This  has  been  described  previously 
on  p.  312. 

Tuba  Auditiva  (O.T.  Eustachian). — The  auditory  tube  is 
the  passage  which  places  the  tympanic  cavity  in  communica- 
tion with  the  pharynx.      Through  it  air  reaches  the  tympanic 


External  meatus 


Tympanic  antrum 
\  Temporal  line 


Mastoid  notch  (O.T. 
Digastric  fossa). 


^Styloid 
process 


Air-cells  in  mastoid  part 
of  temporal  bone 


Fig.  244. 


-Dissection  of  the  Tympanic  Antrum  and  the  mastoid  part  of 
the  temporal  bone  from  the  outer  side. 


cavity  and  antrum  and  the  mastoid  cells.  It  consists  of  an 
osseous  and  a  cartilaginous  portion.  The  osseous  portion  is 
about  half  an  inch  in  length.  It  is  widest  at  its  entrance 
into  the  tympanum,  and  narrowest  at  its  other  end.  The 
cartilagi?wus  portio7i  is  about  an  inch  in  length,  and  has  been 
already  described  on  p.  383. 

Dissection:  Second  Method.— On  the  opposite  side  the  bony  part  of 
the  external  meatus,  the  tympanic  antrum,  and  the  tympanic  cavity  should 
be  approached  from  the  postcro-lateral  aspect.  The  dissection  of  the  bone 
should  be  carried  out  after  the  manner  adopted  by  the  surgeon  when  operat- 
ing for  the  cure  of  extensive  mastoid  and  middle  ear  disease,  but,_  to 
facilitate  the  dissection,  and  to  gain  better  access  to  the  bone,  the  auricle 
may  be  removed  l)y  cutting  through  the  cartilaginous  part  of  the  external 
meatus.  . 

After  the  auricle  has  been  cut  away  clear  all  the  soft  parts,  including 


56o  THE  AUDITORY  APPARATUS 

the  periosteum,  from  the  outer  surface  of  the  mastoid  part  of  the  temporal 
bone,  and  identify  (i)  the  supra-meatal  triangle  and  the  supra-meatal 
spine,  which  lie  at  the  junction  of  the  superior  with  the  posterior  border 
of  the  bony  part  of  the  external  meatus,  and  (2)  the  temporal  line 
which  passes,  posteriorly  and  upwards,  above  the  supra-meatal  triangle. 
The  objects  of  the  first  stage  of  the  dissection  are  (i)  the  removal  of  the 
outer  compact  layer  ;  (2)  the  opening  up  of  the  cancellous  tissue  of  the 
mastoid  part  of  the  temporal  bone,  and  the  exposure  of  the  mastoid  air- 
cells  and  the  cavity  of  the  tympanic  antrum,  whilst,  at  the  same  time, 
injury  to  the  posterior  wall  of  the  bony  part  of  the  external  meatus  and 
to  the  sigmoid  part  of  the  transverse  sinus,  which  lies  in  a  groove  on  the 
inner  aspect  of  the  posterior  part  of  the  mastoid  portion  of  the  temporal 
bone,  is  avoided.  The  tympanic  antrum  lies  at  the  level  of  the  supra- 
meatal  triangle,  that  is  above  and  posterior  to  the  external  meatus,  and 

Lateral  semicircular  canal  Posterior  semicircular  canal 

Reniains  of  posterior  1  ,     Temporal  line 

wall  or  external  meatus  ; 

i  -      /       /  Wall  of  groove  for 

sigmoid  part  of 
transverse  sinus 


Tympanic  plate 

Styloid  process  ,^        ^^  _^,  ^^^^        Mastoid 
facialis 

Fig.  245. — Dissection  of  the  Tympanic  Antrum  and  the  petro-raastoid  part  of 
the  temporal  bone  from  the  outer  side.  The  arrow  is  passing  through 
the  aditus  from  the  tympanic  antrum  into  the  tympanic  cavity. 

about  half  an  inch  from  the  superficial  surface  of  the  temporal  bone. 
The  dissection  should  be  commenced  above,  below  the  temporal 
line,  and  should  be  carried,  anteriorly  and  medially,  into  the  bone, 
parallel  with  the  posterior  wall  of  the  external  meatus,  until  the  tympanic 
antrum  is  opened  into.  After  the  tympanic  antrum  has  been  identified, 
the  cancellous  tissue  of  the  anterior  part  of  the  mastoid  area  must  be 
gradually  removed  till  the  more  medially  situated  and  more  compact 
bone  is  exposed.  When  this  stage  of  the  dissection  is  completed,  the 
dissector  should  note  the  following  points  : — (i)  In  the  anterior  boundary 
of  the  exposed  area  is  the  compact  posterior  wall  of  the  bony  part  of  the 
external  meatus.  (2)  Posteriorly  is  a  broad  projecting  ridge  indi- 
cating the  position  of  the  groove  which  lodges  the  sigmoid  part  of  the 
transverse  sinus.  (3)  At  the  upper  and  deeper  part  of  the  area  are  the 
medial  wall  of  the  tympanic  antrum  and  the  aditus  leading  into  the  tym- 
panic cavity.  (4)  The  intermediate  area  is  occupied  by  the  remains  of 
the  mastoid  air-cells,  which  may  extend  downwards  to  the  tip  of  the 
mastoid  process.    They  are  continuous  above  with  the  cavity  of  the  tympanic 


TYMPANUM 


561 


antrum.  (5)  On  the  medial  wall  of  the  aditus  and  the  anterior  part  of  the 
medial  wall  of  tlie  tympanic  antrum  is  a  horizontal  ridge  which  indicates 
the  position  of  the  lateral  semicircular  canal  of  the  labyrinth,  and,  below 
it,  on  the  medial  wall  of  the  mouth  of  the  aditus,  is  a  vertical  ridge 
indicating  the  position  of  the  canalis  facialis,  which  lodges  the  important 
facial  nerv'e. 

The  next  stage  of  the  dissection  consists  in  the  removal  of  the  posterior 
wall  of  the  external  meatus,  and  the  exposure  of  the  outer  surface  of  the 
tympanic  membrane  (p.  549).  After  the  tympanic  membrane  has  been 
examined,  a  seeker  should  be  passed  through  the  aditus  into  the  tympanic 
cavity,  and  its  handle  should  be  allowed  to  rest  on  the  lower  part  of  the 
exposed  area  ;  then,  whilst  the  seeker  remains  in  position,  the  remainder  of 
the  posterior  wall  and  the  upper  boundary  of  the  external  meatus,  from 
the  level  of  the  seeker  to  the  level  of  the  roof  of  the  tympanic  antrum,  can 


Superior  semicircular  canal 
Fenestra  vestibuli  I 


Canalis  facialis  (posterior 
horizontal  part) 


Lateral  semicircular  canal 

}     Temporal  line 

-'       Posterior  semicircular  canal 


End  of  canal  for 
tensor  tympani 

End  of  auditory  tube 
Styloid  process 


/  Vertical  part  of  canalis  facialis 

Remains  of  posterior  wall  of  external  meatus 


Fig.  246. — Dissection  of  the  Tympanic  Cavity  and  the  semicircular 
canals  from  the  outer  side. 


be  cut  away  without  fear  of  injury  to  any  important  structure.  The 
dissection  should  be  completed  by  the  removal  of  the  tympanic  membrane 
and  ossicles,  and  when  this  has  been  done  a  very  complete  view  will  be 
obtained  of  the  medial  walls  of  the  tympanic  cavity,  the  aditus,  and  the 
tympanic  antrum.  Anteriorly,  on  the  medial  wall  of  the  tympanic  cavity, 
is  the  promontory,  which  marks  the  position  of  the  first  turn  of  the 
cochlea.  Above  and  posterior  to  the  promontory  is  the  fenestra  vestibuli. 
The  fenestra  cochlea  lies  at  the  lower  and  posterior  part  of  the  promontory, 
in  the  anterior  part  of  a  recess  called  the  fossula  fenestra?  cochleae.  Above 
the  fenestra  vestibuli  is  a  ridge  caused  by  the  posterior  horizontal  part 
of  the  canalis  facialis  ;  this  becomes  continuous,  on  the  medial  wall  of  the 
aditus,  with  the  vertical  ridge  which  indicates  the  position  of  the  vertical 
part  of  the  canal.  Above  the  latter  is  the  horizontal  ridge  due  to  the 
lateral  semicircular  canal.  The  dissector  should  open  the  canalis  facialis 
to  expose  the  facial  nerve  ;  then  he  should  open  the  lateral  semicircular 
canal,  and  afterwards  remove  the  bone  above  and  posterior  to  it  to 
expose  the  walls  of  the  superior  and  posterior  vertical  semicircular  canals 
(Figs.  245,  246). 

VOL.   11 — 36 


562  THE  AUDITORY  APPARATUS 


INTRAPETROUS  PART  OF  THE  FACIAL  NERVE 
AND  THE  ACUSTIC  NERVE. 

The  facial  and  acustic  nerves  have  already  been  traced 
into  the  internal  acustic  meatus  (p.  215).  The  dissector 
should  now  open  up  this  meatus  and  follow  the  facial  nerve 
in  its  course  through  the  petrous  portion  of  the  temporal  bone. 
The  canal  which  it  occupies  is  termed  the  canalis  facialis 
(O.T.  aqueduct  of  Fallopius).  It  begins  at  the  bottom  of 
the  internal  acustic  meatus,  and  opens  on  the  exterior  of 
the  skull  at  the  stylo-mastoid  foramen.  Between  its  com- 
mencement and  termination  it  pursues  a  complicated  course, 
and  this,  combined  with  the  density  of  the  bone,  renders  the 
dissection  very  difficult. 

Dissection. — On  the  side  on  which  the  middle  ear  has  been  opened  from 
the  lateral  aspect  and  the  canalis  facialis  has  already  been  partially  opened 
up,  the  dissector  should  complete  the  dissection  of  the  intrapetrous  part  of 
the  facial  nerve  and  should  examine  the  acustic  nerve. 

Separate  the  temporal  bone  from  the  other  cranial  bones  which  still 
adhere  to  it,  and  fix  it  in  the  natural  position  (in  a  vice  if  possible).  Remove 
the  squamous  portion  by  a  horizontal  saw  cut  at  the  level  of  the  upper 
surface  of  the  petrous  portion.  Make  a  second  horizontal  saw  cut,  im- 
mediately above  the  roof  of  the  internal  acustic  meatus,  and  carry  it 
laterally  into  the  tympanum,  in  which  it  should  emerge  immediately  above 
the  already  opened  canalis  facialis  where  the  latter  lies  above  the  fenestra 
vestibuli.  Then,  with  the  bone  forceps  or  chisel,  remove  the  remains  of  the 
roof  of  the  internal  meatus  and  follow  the  facial  nerve  along  the  canalis 
facialis  to  the  hiatus  canalis  facialis,  and  so  expose  the  ganglion  geniculi. 
Secure  the  branches  which  arise  from  the  ganglion  and  then  follow  the  nerve 
posteriorly  above  the  fenestra  vestibuli.  The  greater  part  of  the  vertical 
portion  of  the  canal  has  already  been  opened  from  the  lateral  aspect ;  the 
remainder  can  now  be  displayed  by  means  of  two  saw  cuts — (i)  a  frontal 
section  (vertical  transverse)  carried  medially  from  the  lateral  surface  of  the 
bone  to  the  posterior  border  of  the  stylo-mastoid  foramen  ;  (2)  a  sagittal  cut 
(vertical  antero-posterior)  carried  from  the  posterior  surface  of  the  bone  to 
meet  cut  (i).  The  portion  of  bone  between  the  two  cuts  must  then  be 
removed,  and  the  dissection  must  be  completed  with  bone  forceps.  Three 
branches  are  given  off  in  this  part  of  the  canal. 

Intrapetrous  Portion  of  the  Facial  Nerve. — As  the  facial 
nerve  traverses  the  petrous  bone,  it  may  be  divided  into  four 
stages,  which  differ  from  one  another  in  the  relations  they 
present  and  in  the  direction  which  they  take.     They  are : — 

1.  A  part  within  the  internal  acustic  meatus. 

2.  A  very  short  part  which  extends  from   the  bottom  of  the  internal 

acustic  meatus  to  the  ganglion  geniculi. 


INTRAPETROUS  PART  OF  FACIAL  NERVE      563 

3.  A  part  which  occupies  that  portion  of  the  canalis  facialis  which  runs 

along  the  niedial  wall  of  the  tymjjanic  cavity. 

4.  A  part   which    extends  vertically  downwards  to  the   stylo-mastoid 

foramen. 

First  Stage. — In  the  internal  acustic  meatus,  the  facial 
nerve  runs  almost  directly  laterally  in  company  with  the 
acustic  nerve.  In  this  stage  of  its  course  it  lies  in  relation 
to  the  upper  and  anterior  part  of  the  acustic  nerve,  and 
its  motor  and  sensory  roots  join.  At  the  bottom  of  the 
acustic  meatus  it  enters  the  canalis  facialis. 


Fig.  247. — Diagram  of  Intrapetrous  part  of  facial  nerve  and  its  connections. 
(Prof.  A.  M.  Paterson. ) 

I.  Nerve  to  stapedius.  2.  Chorda  tympaui.  3.  Tympanic  plexus.  4.  Communication 
to  small  superficial  petrosal  nerve.  5.  Ganglion  geniculi.  6.  Motor  part  of 
facial  nerve.  7.  Sensory  part  of  facial  nerve.  8.  Acustic  nerve.  9.  External 
petrosal  nerve.  10.  Great  superficial  petrosal  nerve.  11.  Carotid  canal.  12. 
Carolico-tympanic  branch.  13.  Carotid  plexus.  14.  Great  deep  petrosal.  15. 
Nerve  of  pterygoid  canal.  16  and  18.  Spheno-palatine  branches.  17.  Maxillary 
nerve.  19.  Spheno-palatine  ganglion.  20.  External  petrosal.  21.  Middle 
meningeal  artery.  22.  Otic  ganglion.  23  and  24.  Branches  to  auriculo-temporal 
nerve.  25.  Communication  to  chorda  tympani.  26.  Posterior  division  of 
mandibular  nerve.  27.  Anterior  division  of  mandibular  nerve.  28.  Lingual  nerve. 
29.  Inferior  alveolar  nerve.  30.  Auriculo-temporal  nerve.  31.  Tympanic  branch 
of  glossopharyngeal.  32.  Glossopharyngeal  nerve.  33.  Vagus.  34.  Auricular 
branch  of  vagus.  35.  Communication  from  facial  to  auricular  branch  of  vagus. 
36.  Nerve  to  digastric  (post,  belly).  37.  Nerve  to  stylo -hyoid  muscle.  38. 
Posterior  auricular  nerve. 

Second  Stage. — The  second  part  of  the  facial  nerve  is  very 
short.  It  runs  laterally,  with  a  slight  inclination  anteriorly, 
between  the  vestibule  and  cochlea,  and  very  soon  ends  in 
the  swelling  termed  the  ganglion  geniculi. 

Third  Stage. — At  the  ganglion  geniculi,  the  facial  nerve 
bends     suddenly     and     proceeds     posteriorly     and     slightly 


564  THE  AUDITORY  APPARATUS 

downwards  in  that  portion  of  the  canal  which  runs  along 
the  upper  part  of  the  medial  wall  of  the  tympanic  cavity, 
immediately  above  the  fenestra  vestibuli  (O.T.  ovalis). 

The  first  three  portions  of  the  facial  nerve  are  nearly 
horizontal,  and  pursue  a  somewhat  V-shaped  course.  The 
apex  of  the  V  is  directed  anteriorly,  and  corresponds  to  the 
ganglion  geniculi. 

Th.Q  fourth  stage  is  vertical,  and  arches  downwards,  posterior 
to  the  pyramid,  to  gain  the  stylo-mastoid  foramen. 

The  branches  which  spring  from  or  join  the  facial  nerve 
during  its  passage  through  the  temporal  bone  are : — 


The  greater  superficial  petrosal -netA?:e,  ^ 

Communicating  twig  to  the  sm^Jlei;^  superficial  I  from  ganglion 
petrosal,  '■   ';^ ^        |       geniculi, 

)SxJ 


3.  External  superficial  petrosal  nerve, 

4.  Nerve  to  stapedius.  "^  '■'■^'\ 

5.  Chorda  tympani.  ''"  '^        \'\ 

6.  Communicating  twigs  to  the  auricular  /hj'anch  ofvAgus. 

The  great  superficial  petrosal/  neri^e  hasll  been  examined 
already  (p.  212).  Its  origin  from  ^ije  gangjion  geniculi  of 
the  facial  can  now  be  seen.  / 

The  communicating  branch  X.o  the  small  superficial  petrosal 
arises  from  the  ganglion  geniculi,  and  unites  with  the  fibres 
of  the  tympanic  nerve  which  issue  from  the  tympanic  plexus. 

The  external  petrosal  nerve  is  not  always  present.  It 
joins  the  sympathetic  plexus  which  accompanies  the  middle 
meningeal  artery. 

The  nerve  to  the  stapedius  muscle  arises  from  the  facial  as 
it  arches  downwards  posterior  to  the  pyramid.  It  enters  the 
base  of  the  pyramid  and  thus  reaches  the  stapedius  muscle. 

The  communicating  twigs  to  the  auricular  branch  of  the 
vagus  arise  a  short  distance  above  the  stylo-mastoid  foramen. 

Chorda  Tympani. — The  chorda  tympani  represents  to  a 
large  extent  the  sensory  fibres  set  free  from  the  trunk  of 
the  facial  nerve.  It  is  the  largest  branch  given  off  by  the 
facial  during  its  passage  through  the  canalis  facialis.  It  takes 
origin  a  short  distance  above  the  stylo-mastoid  foramen,  and 
arching  upwards  and  anteriorly,  in  a  narrow  canal  in  the 
petrous  portion  of  the  temporal  bone  (the  canaliculus  chordae 
tympani),  it  appears  in  the  tympanum  by  passing  through 
the  tympanic  aperture  of  the  canaliculus  chordae  below  the 
base  of  the  pyramid,   and  close  to  the  posterior   margin   of 


ACUS'I'IC  NERVE  565 

membrana  tympani.  The  bony  tunnel  which  it  occupies  can 
easily  be  opened  up  in  a  decalcified  bone,  but  is  somewhat 
difficult  to  expose  in  the  hard  bone.  After  entering  the 
tympanum  the  chorda  tympani  runs  anteriorly  upon  the  upper 
part  of  the  membrana  tympani  under  cover  of  the  mucous 
layer.  It  crosses  the  handle  of  the  malleus  on  the  medial 
aspect  near  its  root.  Finally,  reaching  the  anterior  end  of 
the  tympanic  cavity  it  crosses  the  anterior  process  (O.T. 
gracilis)  of  the  malleus,  passes  above  the  tensor  tympani,  and 
traverses  the  medial  end  of  the  petro-tympanic  fissure,  which 
conducts  it  to  the  exterior  of  the  skull.  From  this  point  to 
its  junction  with  the  lingual  nerve  the  chorda  tympani  has 
already  been  traced  (p.  278). 

Acustic  Nerve.  —  In  the  internal  acustic  meatus  the 
acustic  nerve  lies  at  a  lower  level  than  the  facial,  and  at  the 
bottom  of  the  passage  it  splits  into  two  parts,  termed  the 
cochlear  and  vestibular  divisions.  These  trunks  again  sub- 
divide and  supply  the  different  parts,  of  the  labyrinth  of  the 
ear  through  the  foramina  of  the  lamina  cribrosa. 

After  the  examination  of  the  intrapetrous  part  of  the  facial  nerve  and 
the  acustic  nerve  is  completed  the  dissector  should  display  the  labyrinth 
of  the  internal  ear  by  means  of  two  saw  cuts — (i)  an  antero-posterior 
vertical  cut  carried  from  the  upper  surface  of  the  bone  downwards  to 
the  floor  of  the  tympanum  along  the  junction  of  its  medial  and  posterior 
boundaries  ;  (2)  a  horizontal  cut.  This  cut  should  be  commenced  at  the 
apex  of  the  petrous  part  of  the  temporal  bone  and  should  be  carried 
laterally  till  it  joins  the  vertical  cut  posteriorly,  and  enters  the  tympanic 
cavity  anteriorly  at  the  level  of  the  mid-height  of  the  promontory. 
When  the  upper  part  of  the  petrous  portion  of  the  temporal  bone,  separated 
by  the  two  cuts,  is  removed,  the  vestibular  and  cochlear  parts  of  the 
labyrinth  and  portions  of  the  semicircular  canals  will  be  displayed.  The 
dissector  should  demonstrate  the  positions  and  curves  of  the  semicircular 
canals  and  the  canalis  facialis  by  passing  bristles  through  them. 

Amis  Interna. — The  internal  ear  or  labyrinth  consists  of  an 
intricate  system  of  cavities  in  the  petrous  part  of  the  temporal 
bone,  the  osseous  labyrinth^  and  a  series  of  hollow  membranous 
structures,  connected  with  the  filaments  of  the  acustic  nerve, 
which  lie  in  the  osseous  labyrinth  and  constitute  the  7nem- 
branous  labyri7ith. 

The  osseous  labyriiith  is  composed  of  an  intermediate 
chamber  termed  the  vestibule,  posterior  to  which  are  placed 
the  three  semicircular  canals,  whilst  anteriorly  is  the  cochlea. 
All  these  cavities  communicate  with  one  another.  The  corre- 
sponding membranous  parts  do  not  completely  occupy  the 
II— 36« 


566 


THE  AUDITORY  APPARATUS 


osseous  chambers,  and  the  intervening  space  is  filled  with  a 
fluid  termed  the  perily??iph.  The  membranous  labyrinth  also 
contains  a  fluid  which  receives  the  name  of  endolymph. 

Vestibulum. — ^The  vestibule  is  a  small  ovoid  bony  chamber, 
possessing  an  antero -posterior  diameter  of  about  one -sixth 
of  an  inch.  It  is  situated  between  the  medial  wall  of  the 
tympanum  and  the  bottom  of  the  internal  acustic  meatus. 

Into  the  posterior  part  of  the  vestibule  the  three  semi- 
circular canals  open  by  five  round  apertures;  whilst  in  its 
lower  and  anterior  part  is  the  opening  of  the  scala  vestibuU 
of  the  cochlea. 

Recessus  ellipticus 

Crista  vestibuli 

Superior  semi- 


Recessus  sphaericus 


Scala  tympani 
Lamina  spiralis  ossea  j 
Scala  vestibuli 

Opening  of 
aquaeductus  cochleae 

Fenestra  cochleae 
Recessus  cochlearis 


circular  canal 


Lateral  semi- 
circular canal 


Posterior  semi- 
circular canal 


Opening  of  crus  commune 
Opening  of  aquaeductus  vestibuli 


Fig.  248. — Interior  of  the  Left  Bony  Labyrinth  viewed  from 
the  lateral  aspect.      (Howden. ) 

On  the  lateral  wall'is  the  fenestra  vestibuli,  which  is  closed, 
in  the  recent  state,  by  the  delicate  periosteal  lining  of  the 
chamber  and  the  base  of  the  stapes.  When  these  parts  are 
removed,  the  vestibule  communicates  directly  with  the  tym- 
panum. On  the  anterior  part  of  the  medial  wall  of  the 
vestibule  there  is  a  circular  depression,  termed  the  recessus 
sphcericus,  which  is  bounded  posteriorly  by  a  vertical  ridge, 
called  the  crista  vestibuli.  The  bottom  of  the  recessus  sphaericus 
is  perforated  by  some  minute  holes  which  give  admission  to 
filaments  from  the  acustic  nerve.  On  the  roofoi  the  vestibule 
is  another  depression,  named  the  recessus  ellipticus.  It  is  placed 
posterior  to  the  crista  vestibuli. 

A  small  aperture  placed  on  the  posterior  part  of  the 
medial  wall  also  deserves  mention.  It  is  the  mouth  of  the 
aquceductus  vestibuli — a  small  canal  which  leads  posteriorly  to 


LABYRINTH 


567 


the  posterior  surface  of  the  petrous  part  of  the  temporal  bone, 
where  it  opens  under  the  dura  mater. 

Canales  Semicirculares  Ossei.— These  are  three  bony  canals 
or  tubes  placed  posterior  to  the  vestibule.  They  are  bent 
upon  themselves,  so  that  each  forms  considerably  more  than 
half  a  circle,  and  they  occupy  planes  at  right  angles  to  each 
other  like  three  faces  of  a  cube.  They  are  termed  superior, 
posterior,  and  lateral,  and  they  open  into  the  posterior  part 
of  the  vestibule  by  five  round  orifices,  the  number  of  openings 
being  thus  reduced  through  the  adjoining  extremities  of  the 
superior  and  posterior  canals  becoming  fused  together  so  as 
to  present  a  common  canal,  the  cms  couwiune,  with  a  single 

Superior  semicircular  canal 
with  its  ampulla 


Canalis 
facialis 


Cochlea 

Fenestra  cochlea; 
Fenestra  vestibuii 

Ampulla  of  posterior  semicircular  cana. 

Ampulla  of  lateral  semicircular  canal 


Posterior  semi- 
circular canal 
Crus  commune 

Lateral  semicircular  canal 


Fig.  249. — Left  Bony  Lab}Tinth  viewed  from  lateral  side.      (Howden.) 

orifice.  One  extremity  of  each  canal  where  it  joins  the 
vestibule  becomes  expanded  into  what  is  termed  its  ampulla. 
There  are  thus  three  ampullated  ends. 

The  superior  semicircular  canal  forms  the  highest  part  of 
the  labyrinth,  and  gives  rise  to  a  smooth  elevation  on  the 
anterior  surface  of  the  petrous  part  of  the  temporal  bone, 
immediately  anterior  to  its  superior  angle.  It  is  vertical, 
and  placed  almost  transversely  to  the  long  axis  of  the  petrous 
part  of  the  temporal  bone.  The  posterior  semicircular  ca?ial, 
which  is  the  longest  of  the  three  tubes,  is  also  vertical,  and 
lies  in  a  plane  parallel  to  the  posterior^surface  of  the  petrous 
part  of  the  temporal  bone.  The  lateral  semicircular  canal  is 
the  shortest  of  the  tubes,  and  it  lies  in  a  horizontal  plane. 

Cochlea. — The  cochlea  is  a  tapering  tube  which  is  coiled 


568  THE  AUDITORY  APPARATUS 

spirally  for  two  turns  and  a  half  around  a  central  pillar,  termed 
the  modiolus.  The  appearance  produced  is  somewhat  similar 
to  that  of  a  spiral  shell.  The  cochlea  hes  anterior  to  the 
vestibule,  with  its  base  directed  towards  the  bottom  of  the 
internal  acustic  meatus ;  whilst  its  apex  is  directed  antero- 
laterally,  and  lies  in  close  relation  with  the  canal  for  the 
tensor  tympani  muscle. 

The  cochlear  tube  rapidly  diminishes  in  diameter  as  it 
is  traced  towards  the  apex  of  the  cochlea,  and  its  closed 
extremity  is  termed  the  cupola.  The  first  turn  which  it 
takes  around  the  modiolus  produces  the  bulging  on  the 
medial  wall  of  the  tympanum,  which  has  been  described  under 
the  name  of  the  promontory. 

The  modiolus  is  thick  at  the  base,  but  rapidly  tapers 
towards  the  apex.  Its  base  abuts  against  the  bottom  of 
the  internal  acustic  meatus.  It  forms  the  inner  wall  of 
the  cochlear  tube,  and  winding  spirally  round  it,  like  the 
thread  of  a  screw,  is  a  thin  lamina  of  bone,  termed  the  laj?iina 
spiralis,  which  partially  subdivides  the  tube  into  two  passages. 

Numerous  minute  canals  traverse  the  modiolus,  and  one  more  con- 
spicuous than  the  others,  the  longitudinal  cattal  of  the  modiolus^  extends 
along  its  centre.  The  spiral  lamina  also  is  tunnelled  by  small  canals 
in  communication  with  those  in  the  modiolus,  whilst  one,  the  spiral 
canal  of  the  modiolus,  winds  spirally  around  the  central  pillar  in  the 
attached  margin  of  the  spiral  lamina.  All  these  channels  convey 
filaments  from  the  cochlear  division  of  the  acustic  nerve  to  the  membranous 
cochlea,  whilst  the  spiral  canal  lodges  the  ganglion  spirale  cochlece,  which 
is  the  peripheral  ganglion  of  the  cochlear  part  of  the  acustic  nerve. 

The  membranous  cochlear  tube  or  ductus  cochlearis  is  placed 
between  the  free  margin  of  the  spiral  lamina  and  the 
opposite  side  of  the  wall  of  the  cochlear  tube,  and  completes 
the  subdivision  of  the  bony  cochlea  into  two  compartments, 
which  are  termed  the  scala  tympani  and  the  scala  vestibuli. 
The  scala  tympani  is  the  larger  of  the  two.  It  begins  at  the 
fenestra  cochlese,  where  the  secondary  membrane  of  the 
tympanum  shuts  it  off  from  the  tympanic  cavity.  At  the 
apex  of  the  cochlea  it  communicates  with  the  scala  vestibuli 
by  means  of  an  aperture,  termed  the  helicotrema.  At  the 
base  of  the  cochlea  the  scala  vestibuli  communicates  with 
the  lower  and  anterior  part  of  the  vestibule.  The  perilymph 
therefore,  in  the  semicircular  canals  and  vestibule,  is 
directly  continuous  with  that  in  the  scala  vestibuli  and 
scala  tympani. 


LABYRINTH 


569 


It  can  now  be  understood  how  vibrations  of  the  membrana  tympani 
are  communicated  to  the  perilymph  within  the  o^ff^^^/^^^fXts  the 
chain  of  auditory  ossicles  through  the  base  of  the  stapes  affects  the 
Symi  h  in  the  vestibule.  The  vibrations  of  the  perilymph  passing 
aW  the  scala  vestibuli  into  the  scala  tympani  in  turn  affect  the  secondary 
membrane  of  the  tympanum  which  is  stretched  across  the  fenestra  cocWe^. 
With  every  inward  movement  of  the  membrana  tympani  and  ot  the  base 
of  the  stapes,  there  is  an  outward  movement  of  the  membrane  ot  the 
fenestra  codilex,  and  vice  versa.  The  vibrations  of  the  perilymph  affect 
the  Sdolymph  iA  the  membranous  labyrinth,  and  thus  excite  thetermma- 
tions  of  the  acustic  nerve. 


Ductus  endolymphaticus 


mater 


Osseous 
cochlea 


Osseous 

semicircular 

canal 


Membranous 

semicircular 

canal 


A  Stapes 

Fenestra  cochleae 

Aquseductus  cochleae 


Modiolus 


Fig.  250.— Diagram  of  the  Osseous  and  Membranous  Labyrinth. 
(Modified  from  Testut.) 


U.  Utricle. 


^.   Saccule. 


D.C.  Ductus  cochlearis. 


Membranous  Labyrinth.  —  In  the  vestibule  there  are  two  mem- 
branous sacs,  termed  the  utricle  and  the  saccule.  The  tttride  occupies 
the  recessus  elHpticus  on  the  wall  of  the  vestibule,  and  hes  above  and 
posterior    to   the    saccule.     Into    it    open    the    membranous    semicircular 

"^""'The  saccule  is  smaller,  and  occupies  the  recessus  sphrericus  on  the  anterior 
part  of  the  medial  wall  of  the  vestibule.  It  communicates  by  means  ot  a 
short  narrow  tube,  termed  the  canalis  reufiiens,  with  the  ductus  cochlearis 
or  membranous  cochlear  tube.  ,     .   , 

The  saccule  and  the  utricle  are  only  indirectly  brought  into  communica- 
tion with  each  other  ;  a  slender  tube  termed  the  ductus  endolymphaticus 
occupies  the  aquicductus  vestibuli,  and  divides  into  two  Dranches  which 
pass  respectively  into  the  saccule  and  the  utricle  (Fig.  250). 

The  ductus  cochlearis,  or  scala  media,  lies  between  the  two  scalce  of  the 
cochlear  tube.  It  ends  blindly  at  each  extremity,  but  close  to  its  basal 
end  it  is  brought  into  communication  with  the  saccule  by  the  canalis 
reuniens. 


570  BULBUS  OCULI 


BULBUS  OCULI. 

The  bulbus  oculi  or  eyeball  is  not  perfectly  spherical ;  it  may 
be  said  to  be  composed  of  the  segments  of  two  spheres. 
The  anterior  or  corneal  segment,  forming  only  about  one-sixth 
of  the  entire  eyeball,  possesses  a  shorter  radius  than  the  pos- 
terior or  scleral  segment.  The  anterior  clear  corneal  part  of 
the  eyeball  forms,  therefore,  a  dome-like  bulging  or  prominence 
on  the  front  of  the  globe  of  the  eye.  The  terms  anterior 
diXi^L  posterior  pole  are  respectively  applied  to  the  central  points 
of  the  anterior  and  posterior  segments  of  the  eyeball.  The 
imaginary  line  which  joins  these  poles  receives  the  name 
of  the  sagittal  axis,  whilst  another  line  drawn  in  a  coronal 
direction  around  the  globe  of  the  eye  midway  between  the 
two  poles  so  as  to  divide  the  eyeball  into  two  hemispheres 
is  termed  the  equator.  Imaginary  meridional  lines  also  are 
drawn  between  the  two  poles  so  as  to  cut  the  equatorial  line 
at  right  angles. 

Dissection  of  the  Eyeball. — A  satisfactory  dissection  of  the  globe  of  the 
eye  can  be  made  only  when  the  eyeball  is  fresh,  or  after  it  has  been 
hardened  for  several  days  in  a  lO  %  solution  of  formol.  In  the  dissecting- 
room  it  is  often  impossible  to  obtain  suitable  specimens  ;  but  it  is  always 
easy  to  procure  eyeballs  of  the  pig,  sheep,  or  ox,  and  these  suit  the  purpose 
admirably.  It  is  advisable,  however,  that  the  dissector  should  complete 
his  study  of  the  organ  by  the  examination  of  a  fresh  human  eyeball  obtained 
from  the  post-mortem  room.  In  point  of  size,  and  also  in  other  particulars, 
the  eyeball  of  the  pig  more  closely  resembles  the  human  eyeball,  but  it 
is  perhaps  better  that  the  student  should  begin  with  the  eyeball  of  the 
ox,  seeing  that  in  it  the  dissection  can  be  more  easily  carried  out. 

When  the  dissector  has  provided  himself  with  six  eyeballs  obtained  from 
oxen,  he  should  remove  from  them  the  conjunctiva,  fascia  bulbi,  ocular 
muscles,  and  fat,  which  adhere  to  them.  Pinching  up,  with  the  forceps, 
the  conjunctiva  and  the  fascia  bulbi  close  to  the  corneal  margin,  he  should 
snip  through  these  layers  with  the  scissors  and  divide  them  round  the 
whole  edge  of  the  cornea.  He  can  then  easily  strip  all  the  soft  parts 
from  the  surface  of  the  sclera,  working  steadily  posteriorly  towards  the 
entrance  of  the  optic  nerve.  A  little  posterior  to  the  equator  of  the 
eyeball  the  venae  vorticosae  will  be  noticed  issuing  from  the  sclera  at  wide 
intervals  from  each  other,  and  on  approaching  the  posterior  aspect  of  the 
eyeball  the  posterior  ciliary  arteries  and  the  ciliary  nerves  will  be  seen 
piercing  the  sclera  around  the  entrance  of  the  optic  nerve. 

Before  beginning  the  actual  dissection  of  the  eyeball,  it  is  important 
that  the  student  should  obtain  a  general  conception  of  the  parts  which 
compose  it.  This  can  be  done  by  sections  through  three  hardened  speci- 
mens in  three  different  planes.  One  specimen  may  be  divided  at  the 
equator  into  an  anterior  and  a  posterior  portion.     Another  may  be  divided 


EYEBALL 


571 


in  an  antero- posterior  direction  into  a  medial  and  a  lateral  half.  A  third 
should  be  divided  horizontally  and  a  portion  of  the  vitreous  body  should  be 
removed  {Fig.  251).  When  the  sections  are  made,  they  should  be  placed 
under  water  in  a  cork-lined  tray,  and  preserved  for  reference  as  the  study 
of  the  eyeball  is  proceeded  with. 

General  Structure  of  the  Eyeball. — The  eyeball  consists 
of  three  concentrically  arranged  coats  enclosing  a  cavity  in 
which  three  refracting  media  are  placed. 

The  tunics  are:  (i)  an  external  fibrous  envelope  com- 
posed of  a  posterior  opaque  part,  called  the  sdera,  and  an 


Anterior  chamber 
Iris    'i 

Posterior  chamber 
Ciliary  body 
Corona  ciliaris 


Pupil 
i    Lens 


Cornea 

Zonula  ciliaris 

\  enous  sinus  of  sclera 
Conjunctiva 


Ora  serrata 


Retina  with 

vessels 


Reti 


Chorioid 


Vitreous  body 


Sclera 


"•~  Hyaloid  canal 


fT~  Op 


Central  fovea 
tic  nerve 


Fig.  251. — Diagrammatic  section  of  Eyeball. 

anterior  clear  transparent  portion  called  the  cornea;  (2)  an 
intermediate  vascular  envelope  known  as  the  itveal  tract.,  in 
w^hich  three  subdivisions  are  recognised,  viz.,  a  posterior  part 
called  the  chorioid.,  an  anterior  portion  termed  the  iris.,  which 
lies  posterior  to  the  cornea,  and  an  intermediate  ciliary  body ; 
(3)  the  nervous  internal  tunic  or  retina.,  in  which  the  fibres 
of  the  optic  nerve  spread  out. 

The  refracting  media  are:  (i)  posterior  to  the  cornea  a 
watery  fluid,  called  the  aqueous  humour.,  contained  in  a 
space  partially  subdivided  by  the  iris  into  the  two  chambers 
of  the  eye;  (2)  the  crystalline  lens  posterior  to  the  posterior 


572  BULBUS  OCULI 

chamber;  and  (3)  the  vitreous  body^  occupying  the  posterior 
part  of  the  interior  of  the  eyeball.  "* 

Dissection. — The  superficial  surface  of  the  sclera  and  the  cornea 
should  now  be  examined  ;  but  to  complete  the  study  of  the  external  tunic 
a  further  dissection  is  required.  Selecting  an  eyeball  for  this  purpose,  an 
incision  should  be  made,  with  a  sharp  knife,  through  the  sclera  at  the 
equator.  This  must  be  done  carefully,  and  the  moment  that  the  sub- 
jacent black  chorioid  coat  appears  the  knife  should  be  laid  aside.  The  cut 
edge  of  the  sclera  should  now  be  seized  with  the  forceps,  and  the  incision 
carried  completely  round  the  eyeball,  with  the  scissors,  along  the  line  of  the 
equator.  The  outer  fibrous  tunic  is  thus  divided  into  an  anterior  and 
a  posterior  portion.  These  must  now  be  raised  from  the  subjacent  parts. 
As  the  anterior  portion  is  turned  anteriorly,  some  resistance  will  be  met 
close  to  the  margin  of  the  cornea  from  the  attachment  of  the  ciliary  muscle 
to  the  deep  surface  of  the  sclera.  This  can  easily  be  broken  through  with 
the  blunt  point  of  the  closed  forceps  ;  as  soon  as  this  is  done  the  aqueous 
humour  escapes.  In  the  case  of  the  posterior  part  of  the  sclera,  its 
complete  separation  can  be  effected  by  dividing  the  fibres  of  the  optic 
nerve  close  to  the  point  where  they  appear  through  the  sclera. 

When  the  above  dissection  is  successfully  carried  out,  the  outer  fibrous 
tunic  is  isolated  in  two  portions,  whilst  a  continuous  view  of  the  inter- 
mediate vascular  coat  is  obtained.  The  eyeball,  denuded  of  its  external 
tunic,  should  now  be  placed  in  a  shallow  vessel  filled  with  water. 

Sclera. — The  sclera  is  what  is  commonly  known  as  the 
white  of  the  eye.  It  is  a  dense,  resistant  tunic,  opaque- 
white  in  colour,  which  envelops  the  posterior  five-sixths  of 
the  globe  of  the  eye.  It  is  thickest  posteriorly,  and  becomes 
thinner  as  it  is  traced  anteriorly.  Near  the  cornea,  however, 
it  again  becomes  thicker,  owing  to  the  accession  of  fibres 
which  it  receives  from  the  tendons  of  the  ocular  muscles. 
Except  at  the  optic  entrance  and  close  to  the  margin  of 
the  cornea,  where  it  adheres  to  the  surface  of  the  subjacent 
ciliary  muscle,  the  deep  surface  of  the  sclera  is  very  loosely 
attached  to  the  chorioid  coat.  Some  pigmented  flocculent 
connective  tissue,  the  lamina  fusca^  passes  between  the  two 
coats  and  traverses  what  is  in  reality  an  extensive  lymph 
space,  termed  the  perichorioidal  space. 

The  point  at  which  the  optic  nerve  pierces  the  sclera 
does  not  correspond  with  the  posterior  pole  of  the  eyeball. 
The  optic  entrance.,  as  it  is  termed,  is  situated  about  3  mm.  to 
the  medial  or  nasal  side  of  the  posterior  pole  and  i  mm. 
below  it.  There  the  outer  fibrous  sheath  of  the  optic 
nerve,  which  is  derived  from  the  dura  mater,  blends  with 
the  sclera,  and  the  bundles  of  nerve  fibres  pass  through  a 
series  of  small  apertures.  This  perforated  portion  of  the 
sclera  is  called  the  lamina  cribrosa. 


CORNEA 


573 


The  sclera  is  pierced  also  by  numerous  blood-vessels  and  nerves. 
The  long  and  short  posterior  ciliary  arteries  with  the  ciliary  nerves 
perforate  the  sclera  around  the  optic  entrance  ;  four  or  five  vense 
vorticosce  issue  from  the  interior  of  the  eyeball  by  piercing  the  sclera  a 
short  distance  posterior  to  the  equator,  at  wide  intervals  from  each  other  ; 
whilst  the  anterior  ciliary  arteries  pierce  it  near  the  corneal  margin. 

Anteriorly  the  sclera  is  not  only  contiguous  to,  but  is 
directly  and  structurally  continuous  with,  the  cornea.  This 
is  termed  the  corfieo-scleral  j'unctmi,  and  the  faint  groove  on 
the  surface,  which  corresponds  with  it,  receives  the  name  of 
the  scleral  sulcus.  At  this  junction  the  scleral  tissue  slightly 
overlaps    the    corneal   tissue,    and    the   line   of  union,  when 


Vena  vorticosa 


Long  posterior 
ciliary  arteries 


Optic  entrance 
Short  ciliary 
'arteries  and 
ciliary  nerves 


Fig.  252. — Diagram  of  the  posterior  aspect  of  the  Left  Eyeball.      The 
excentric  position  of  the  optic  entrance  is  somewhat  exaggerated. 

(After  Testut,  modified.) 

seen  in  section,  is  oblique.  Close  to  this  a  minute  canal  in 
the  substance  of  the  sclera,  termed  the  si?ius  venosus  sclerce 
(O.T.  canal  of  Schlemm),  encircles  the  margin  of  the  cornea. 
Cornea. — The  cornea  forms  the  anterior  sixth  of  the  outer 
tunic  of  the  eye.  It  is  transparent  and  glass-like,  and  it 
forms  the  window  through  which  the  rays  of  light  gain 
admittance  into  the  eyeball.  The  curvature  of  the  cornea  is 
more  accentuated  than  that  of  the  sclera,  and  thus  it  consti- 
tutes the  segment  of  a  smaller  sphere.  When  viewed  from 
the  posterior  aspect  it  appears  circular,  but  when  looked  at 
from  the  front  it  is  seen  to  be  slightly  wider  in  the  transverse 
direction.  This  is  due  to  the  fact  that  the  sclera  overlaps  it 
to  a  greater  extent  above  and  below  than  it  does  at  the  sides. 
The  posterior  concave  surface  of  the  cornea  forms  the  anterior 


5  74  BULBUS  OCULI 

boundary  of  the  anterior  chamber  of  the  eyeball,  and  is 
separated  by  the  aqueous  humour  from  the  anterior  surface 
of  the  iris. 

The  anterior  convex  surface  of  the  cornea  is  clothed  with 
the  conjunctiva,  reduced  to  a  transparent  epithelial  layer. 
On  its  posterior  aspect  there  is  an  elastic  glassy  stratum, 
termed  the  posterior  elastic  lamina.  When  the  cornea  is 
relaxed  this  membrane  becomes  wrinkled,  and  it  can  be 
torn  away  in  shreds  from  the  proper  corneal  tissue. 

Ligamentum  Pectinatum  Iridis. — At  the  margin  of  the 
cornea  the  posterior  elastic  lamina  is  fibrillar,  and  some  of 
its  fibres  are  continued  into  the  iris,  forming  the  liga??jentum 
pectinatum  iridis.,  whilst  others  are  prolonged  posteriorly  into 
the  chorioid  and  the  sclera.  The  ligamentum  pectinatum 
iridis  bridges  across  the  angle  between  the  cornea  and  the 
iris,  and  the  bundles  of  fibres  into  which  the  posterior  elastic 
lamina  breaks  up  in  this  region  constitute  an  annular  mesh- 
work  or  sponge-like  series  of  minute  spaces  termed  the  spatia 
anguli  iridis  (O.T.  spaces  of  Fontana).  These  communicate 
with  the  anterior  chamber  of  the  eyeball,  and  are  filled  with 
aqueous  humour. 

Tunica  Vasculosa  Oculi. — The  intermediate  or  vascular 
tunic,  frequently  spoken  of  as  the  uveal  tract,  is  exposed, 
in  its  entire  extent,  in  the  eyeball  from  which  the  sclera 
and  the  cornea  have  been  removed.  It  is  separable  into 
three  parts — (i)  a  posterior  portion,  the  chorioidea;  (2) 
an  intermediate  part,  the  corpus  ciliare ;  and  (3)  an  anterior 
segment,  the  iris. 

Chorioidea. — The  chorioid  is  the  largest  part  of  the  vas- 
cular tunic.  It  lines  the  posterior  segment  of  the  eyeball, 
between  the  sclera  externally  and  the  retina  internally.  It 
is  thickest  posteriorly,  where  it  is  pierced  by  the  optic  nerve, 
and  becomes  thinner  anteriorly,  as  it  approaches  its  union 
with  the  ciliary  body.  Its  superficial  surface  is  connected 
with  the  deep  surface  of  the  sclera  by  some  lax  connective 
tissue,  and  also  by  blood-vessels  and  nerves  which  pass  from 
the  one  into  the  other.  The  deep  surface  of  the  chorioid  is 
moulded  upon  the  retina  and  connected  with  a  layer  of 
deeply-pigmented  cells  which  usually  adheres  to  the  chorioid 
when  that  tunic  is  removed,  although  in  reality  it  is  a  portion 
of  the  retina. 

In  the  eyes  of  many  mammals,  but  not  in  man,  the  posterior  part  of  the 


CILIARY  BODY 


575 


chorioid,  when  viewed  from  the  front,  presents  an  extensive  brightly-coloured 
area,  which  exhibits  a  metallic  lustre.  This  appearance  is  due  to  the 
presence  of  an  additional  layer  in  the  chorioid  termed  the  tapettiin.  In 
the  horse,  elephant,  and  ox,  the  tapetum  is  composed  of  fibres  (tapetum 
fibrosum)  ;  in  carnivora,  it  is  formed  of  cells  (tapetum  cellulosum).  In  the 
ox,  it  is  a  brilliant  green  colour  with  a  golden  lustre  ;  in  the  dog,  it  is  white 
with  a  bluish  border  ;  in  the  horse,  it  is  blue  with  a  silvery  lustre. 

The  chief  bulk  of  the  chorioid  coat  is  composed  of  blood- 
vessels. These  are  arranged  in  two  well-marked  layers,  viz., 
a  deep,  closely-meshed  capillary  layer  called  the  la77iina  chorio- 
capillaris^  and  a  more  superficial  venous  layer  composed  of 


Sinus  venosus  sclerae. 

Anterior  ciliary, 
artery 


Sclera 


Vena  vorticoss 


Long  posterior 
ciliary  arter> 


Anterior  ciliary 
artery 

Ciliary  muscle 


Long  posterior 
ciliary  artery 

ena  vorticosa 


posterior 
ciliary  artery 


Fig.  253. — Dissection  of  the  Eyeball  showing  the  Vascular  Tunic  and 
the  Arrangement  of  the  Ciliary  Nerves  and  Vessels. 

the  vasa  vorticosa.      The  short  posterior  ciliaiy  arteries  pass 
anteriorly  between  these  vascular  layers. 

The  eyeball  in  which  the  outer  surface  of  the  chorioid  is  exposed  should 
be  immersed  in  water  and  the  pigment  washed  out  of  it  by  means  of  a 
camel-hair  brush.  The  vasa  vorticosa  will  then  appear  as  white  curved 
lines  converging  towards  four  or  five  jDoints,  from  which  the  vena  vorticosse 
take  origin  (Fig.  253). 

Corpus  Ciliare. — The  ciliary  body  is  separable  into  an 
antero-external  part,  the  orbiculus  ciliaris,  and  a  postero- 
internal part,  the  corona  ciliaris. 

The  orbiculus  ciliaris  consists  of  the  ciliary  muscle,  the 
ganglionated  ciHary  nerve  plexus,  and  plexuses  of  arteries 
and   veins  associated   with  the  iris   and  ciliary  body.      It  is 


576 


BULBUS  OCULI 


continuous  with  the  iris  internally,  the  sclera  anteriorly,  and 
the  corona  ciharis  and  the  chorioid  posteriorly. 

Ciliary  Muscle. — This  is  composed  of  involuntary  muscular 
tissue,  but  the  arrangement  of  its  fibres  can  be  seen  only 
when  thin  sections  of  the  eyeball  are  examined  under  the 
microscope.  It  is  then  obvious  that  the  fibres  are  disposed 
in  two  groups,  viz.,  a  radiating  and  a  circular. 

The  radiating  fibres  arise  from  the  deep  aspect  of  the 
sclera  close  to  the  margin  of  the  cornea.  From  this 
they  radiate  posteriorly,  in  a  meridional  direction,  and  gain 
insertion  into  the  chorioid  coat  in  the  region  of  the  ciliary 
processes.      The  circular  fibres  consist  of  two  or  three  bundles 


Chorioid 


Sclera  .. 


Zonula 
/Ciliaris 


Ciliary  fold 


Chorioid  (cut 
edge  of) 


t  Lens 


Ciliary  process 


Fig.  254. — Posterior  view  of  Lens  and  Zonula  Ciliaris. 
(Professor  Arthur  Thomson.) 

placed  upon  the  deep  aspect  of  the  radiating  portion  of  the 
muscle.  They  form  a  muscular  ring  around  the  outer  circum- 
ference of  the  iris. 

Dissection.— To  obtain  a  view  of  the  ciliary  processes,  a  frontal  section 
should  be  made  through  an  eyeball  a  short  distance  anterior  to  the 
equator.  The  portion  of  the  vitreous  body  which  occupies  the  posterior 
segment  of  the  eyeball  should  be  carefully  removed.  When  this  is  done 
the  deep  aspect  of  the  corona  ciliaris  will  be  seen.  It  is  covered  with 
ciliary  processes  which  radiate  posteriorly  from  the  circumference  of  the 
crystalline  lens.  By  washing  out  the  pigment  from  this  part  of  the  vascular 
tunic,  the  arrangement  of  the  processes  will  be  displayed  more  fully.  _ 

A  second  dissection  may  be  made  in  another  eyeball  with  the  object  of 
exposing  the  ciliary  processes  from  the  front.  In  this  case  remove  the 
cornea  with  the  scissors  by  cutting  round  the  corneo-scleral  junction.  The 
iris  is  now  brought  conspicuously  into  view,  and  may,  with  advantage,  be 
studied  at  this  stage.     Several  cuts  in  the  meridional  direction,  and   at 


CILIARY  BODY 


577 


equal  intervals  from  each  other,  should,  in  the  next  place,  be  made  through 
the  anterior  part  of  the  sclera.  The  strips  of  sclera  should  then  be 
separated  from  the  ciliary  muscle,  and  pinned  outwards  in  a  cork- 
lined  tray  filled  with  water.  The  last  step  in  the  dissection  consists  in  the 
removal  of  the  iris. 

The  corona  ciliaris  lies  on  the  posterior  aspect  of  the 
orbiculus  ciliaris  and  is  continuous  anteriorly  with  the 
iris  and  posteriorly  with  the  chorioid.  It  consists  of  a  number 
of  larger  folds,  \.\\& processus  ciliares,  70  to  72  in  number,  which 
are  intermingled  with  a  number  of  smaller  folds,   the  pliccE 

Ligamentum  pectinatum  iridis 
Scleral  spur  •  Radial  muscle  of  iris 

Venous  sinus  of  sclera  -,  j  ;  jjjg 

Sclera  -■  '■ 


Meridic 


rnu> 

Iridial  angle 


Parts  of  ciliary  processes 
Circular  fibres  of  ciliarj-  muscle 


Fig.  255. — Section  of  Iridial  Angle.      (Prof.  Arthur  Thomson.) 

ciliares.  The  ciHary  processes  extend  from  the  anterior 
margin  of  the  chorioid  to  the  anterior  margin  of  the  corona 
ciliaris,  where  they  end  in  bulbous  extremities.  The  bulbous 
ends  occupy  the  space  between  the  peripheral  margin  of  the 
iris  and  the  margin  of  the  anterior  surface  of  the  crystalline 
lens,  and  they  form  the  peripheral  boundary  of  the  posterior 
chamber  of  the  eyeball.  The  plic(^  ciliares  are  much  less 
prominent  than  the  ciliary  process,  and  both  the  processes 
and  the  folds  are  in  relation  posteriorly  with  the  hyaloid 
membrane,  which  separates  them  from  the  vitreous  body, 
and  with  the  peripheral  part  of  the  zonula  ciliaris  to  which 
they  are  attached. 
VOL.  II — 37 


578  BULBUS  OCULI 

Iris. — The  iris  lies  anterior  to  the  crystalline  lens,  and  it 
is  separated  from  the  cornea  by  the  anterior  chamber  filled 
with  aqueous  humour.  By  its  circumference  it  is  continuous 
with  the  ciliary  body,  and  it  is  connected  by  the  ligamentum 
pectinatum  iridis  with  the  margin  of  the  cornea. 

The  iris  is  circular  in  form,  and  has  a  central  perforation 
termed  the  pupil.  Its  anterior  surface  is  faintly  striated  in  a 
radial  direction.  It  is  coloured  differently  in  different 
individuals.  Its  posterior  surface  is  deeply  pigmented. 
The  pupil  presents  a  very  nearly  circular  outline,^  and 
during  life  it  constantly  varies  in  its  dimensions  so  as  to 
control  the  amount  of  light  which  is  admitted  into  the 
interior  of  the  eyeball.  These  changes  in  the  size  of  the 
pupil  are  produced  by  the  two  groups  of  involuntary  muscular 
fibres  which  are  present  in  the  substance  of  the  iris.  One 
group  is  composed  of  muscular  fibres  arranged  circularly 
around  the  pupil  in  the  form  of  a  sphincter',  the  second 
group  consists  of  fibres  which  have  a  radial  direction,  and 
pass  from  the  sphincter  towards  the  circumference  of  the 
iris,  so  as  to  constitute  a  dilatator  muscle.  By  some 
anatomists  these  radial  fibres  are  considered  to  be  elastic 
and  not  muscular. 

Ciliary  Nerves. — The  ciliary  nerves  arise  from  the  ciliary 
ganglion  and  the  naso-ciliary  nerve.  They  pierce  the  sclera 
around  the  optic  entrance,  and  extend  anteriorly,  between 
the  sclera  and  the  chorioid,  in  the  perichorioidal  lymph  space. 
They  will  be  seen,  in  the  specimen  in  which  the  sclera  has 
been  turned  aside  in  separate  flaps,  in  the  form  of  dehcate 
white  filaments  (Fig.  253).  In  the  posterior  part  of  the 
eyeball  they  occupy  grooves  on  the  deep  surface  of  the  sclera, 
and  can  be  separated  from  it  only  with  difficulty.  Reaching 
the  ciliary  zone  the  ciliary  nerves  break  into  branches,  which 
join  in  a  plexiform  manner  and  send  twigs  to  the  ciliary 
muscle,  the  iris,  and  the  cornea. 

Ciliary  Arteries.  —  There  are  three  groups  of  ciliary 
arteries: — (i)  the  short  posterior  ciliary  arteries;  (2)  the  long 
posterior  ciliary  arteries;  and  (3)  the  anterior  ciliary  arteries. 

The  short  posterior  ciliary  arteries.,  branches  of  the 
ophthalmic,    pierce    the    sclera    around    the    optic    entrance, 

1  It  may  be  as  well  to  mention  here  that  the  pupil  in  the  ox  and  the 
sheep  is  greatly  elongated  in  the  transverse  direction.  In  the  pig,  how- 
ever, it  is  approximately  circular. 


RETINA 


579 


and   are  distributed   in  the  chorioid  coat   between   the  vasa 
vorticosa  and  the  membrana  chorio-capillaris. 

The  long  posterior  ciliary  arteries^  also  branches  of  the 
ophthalmic,  are  only  two  in  number.  They  perforate  the 
sclera  on  either  side  of  the  optic  nerve  (Fig.  252),  a  short 
distance  beyond  the  short  ciliary  arteries,  and  then  pass 
anteriorly  between  the  sclera  and  the  chorioid.  When 
they  gain  the  ciliary  zone  each  artery  divides  into  an 
ascending  and  a  descending  branch,  and  these,  with  the 
anterior  ciliary  arteries,  form  an  arterial  ring  termed  the 
circuliis  iridis  major.  Branches  are  given  off  from  this  circle 
to  the  ciliary  muscle,  the  ciliary  processes,  and  the  iris. 

The  circtdus  iridis -minor\%  the  name  applied  to  a  second  arterial  ring 
in  the  iris  at  the  outer  border  of  the  sphincter  pupillae. 

The  anterior  ciliary  arteries  are  very  small  twigs,  which 
arise  from  the  branches  of  supply  to  the  recti  muscles. 
They  pierce  the  sclera  close  to  the  margin  of  the  cornea, 
take  part  in  the  formation  of  the  circulus  iridis  major,  and 
send  twigs  to  the  ciliary  processes. 

Venae  Vorticosse. — From  each  venous  vortex  in  the 
chorioid  a  large  vein  arises,  which  makes  its  exit  from  the 
eyeball  by  piercing  the  sclera,  obliquely,  a  short  distance 
posterior  to  the  equator.      They  are  four  or  five  in  number. 

Dissection. — The  vitreous  body  and  retina,  in  the  posterior  part  of  the 
eyeball  which  was  cut  into  two  for  the  purpose  of  exposing  the  ciliary 
processes  from  the  posterior  aspect,  should  now  be  dislodged.  By  raising 
the  chorioid  coat  from  the  deep  surface  of  the  sclera,  under  a  flow  of 
water  from  the  tap,  the  venae  vorticosae  entering  the  deep  surface  of  the 
sclera  will  be  brought  into  view.  When  these  are  divided,  and  the  separa- 
tion of  the  two  coats  is  carried  posteriorly  towards  the  optic  entrance,  the 
posterior  short  ciliary  arteries,  as  they  emerge  from  the  sclera  and  enter  the 
posterior  part  of  the  chorioid,  will  be  seen. 

In  the  eyeball  from  which  the  sclera  and  cornea  have  been  removed, 
the  iris,  ciHary  processes,  and  the  chorioid  should  be  carefully  stripped  off 
piecemeal  under  water.     This  will  expose  the  retina. 

Retina.  —  The  retina  is  composed  of  two  strata — viz.,  a 
thin  pigmentary  layer,  which  adheres  to  the  deep  surface  of 
the  chorioid  coat,  and  has  been  removed  with  it,  and  a 
delicate  nervous  layer,  which  is  moulded  on  the  surface  of 
the  vitreous  body,  but  presents  no  attachment  to  it  except  at 
the  optic  entrance.  The  retina  extends  anteriorly,  beyond 
the  equator  of  the  eyeball,  and,  a  short  distance  from  the 
ciliary   zone,  it    appears   to    end   in   a   well-defined  wavy  or 


58o  BULBUS  OCULI 

festooned  border  termed  the  ora  serrata.  This  appearance, 
however,  is  somewhat  deceptive.  The  nerve  elements,  it 
is  true,  come  to  an  end  along  this  line,  but  a  lamina  in 
continuity  with  the  retina  is  in  reality  prolonged  antero- 
medially  as  far  as  the  margin  of  the  pupil.  The  part  in 
relation  to  the  ciliary  processes  is  exceedingly  thin,  and 
cannot  be  detected  by  the  naked  eye.  It  is  termed  the 
pars  ciliaris  retincE.  The  portion  on  the  deep  surface  of  the 
iris  is  called  the  stratum  pigmenti  iridis. 

During  life  the  retina  proper  is  transparent,  but  after  death 
it  soon  assumes  a  dull  greyish  tint  and  becomes  opaque. 
Posteriorly  it  is  tied  down  at  the  optic  entrance.  When 
viewed  from  the  anterior  aspect  this  appears  as  a' conspicuous 
circular  disc  termed  the  papilla  nervi  optici,  upon  which  is 
a  depression,  the  excavatio  papillce.  From  this  spot  the 
optic  nerve  fibres  radiate  out  so  as  to  form  the  deep  or 
anterior  layer  of  the  retina.  The  optic  disc,  in  correspond- 
ence with  the  entrance  of  the  optic  nerve,  lies  to  the  medial 
or  nasal  side  of  the  antero -posterior  axis  of  the  eyeball. 
Exactly  in  the  centre  of  the  human  retina,  and  therefore  in 
the  axis  of  the  globe  of  the  eye,  there  is  a  small  yellowish 
spot  termed  the  macula  lutea}  It  is  somewhat  oval  in 
outline,  and  a  depression  in  its  centre  is  called  the  fovea 
centralis. 

Retinal  Arteries  and  Veins. — In  a  fresh  eyeball  the 
arteria  centralis  retince  will  be  seen  entering  the  retina  at 
the  optic  disc.  It  immediately  divides  into  a  superior 
and  an  inferior  branch,  and  each  of  these  breaks  up 
into  a  large  lateral  or  temporal  division,  and  a  smaller 
medial  or  nasal  division.  These  ramify  in  the  retina  as  far  as 
the  ora  serrata ;  but  the  resultant  branches  do  not  anastomose 
with  each  other,  nor  with  any  of  the  other  arteries  in  the 
eyeball. 

The  retinal  veins  converge  upon  the  optic  disc,  and 
disappear  into  the  substance  of  the  optic  nerve  in  the  form 
of  two  small  trunks  which  soon  unite. 

The  retinal  vessels,  the  optic  disc,  and  the  macula  can  all  be  examined 
in  the  living  eye  by  means  of  the  ophthalmoscope.  The  red  reflex  obtained 
from  the  fundus  of  the  eyeball  is  produced  by  the  blood  in  the  lamina 
chorio-capillaris. 

^  There  is  no  macula  lutea  in  the  eyeball  of  the  ox  or  sheep. 


VITREOUS  BODY  581 

Dissection. — For  the  study  of  the  vitreous  body  and  the  crystalline  lens, 
which  together  may  be  termed  the  "eye-kernel,"  it  is  better  to  take  an 
eyeball  which  is  not  perfectly  fresh  (Anderson  Stuart).  The  eyeball 
selected  for  this  purpose  should  be  allowed  to  stand  untouched  from  one 
to  three  days,  according  to  the  season.  The  coats  of  the  eye  should  then 
be  divided  round  the  equator,  and  on  gently  separating  the  cut  edges,  and 
turning  the  coats  anteriorly  and  posteriorly,  the  "  eye-kernel "'  will  slip  out. 
It  should  be  allowed  to  drop  into  a  vessel  tilled  with  clean  water.  The 
examination  of  the  parts  forming  the  "  eye-kernel"'  will  be  greatly  facilitated 
by  placing  it  en  masse  in  strong  picro-carmine  solution  for  a  few  minutes. 
When  removed  from  the  staining  fluid,  it  should  be  well  washed  in  water. 
In  this  way  the  hyaloid  membrane  enclosing  the  vitreous  body,  the  capsule 
of  the  lens,  and  the  zonula  ciliaris,  are  stained  red,  and  their  connections 
become  very  apparent  (Anderson  Stuart). 

Vitreous  Body. — This  is  a  soft,  yielding,  transparent, 
jelly-like  body,  which  occupies  the  posterior  four-fifths  of  the 
interior  of  the  eyeball.  The  retina  is  spread  over  its  surface 
as  far  forwards  as  the  ora  serrata,  but  is  in  no  way  attached 
to  it,  except  at  the  optic  disc.  Anterior  to  the  ora  serrata, 
the  ciliary  processes  are  applied  to  the  vitreous  body  and 
indent  its  surface.  j\Iore  anteriorly,  the  vitreous  body  pre- 
sents a  deep  concavity,  the  fossa  kyaloidea,  for  the  reception 
of  the  posterior  convex  surface  of  the  crystalline  lens. 

The  substance  of  the  vitreous  body  is  enclosed  within  a 
delicate  transparent  membrane,  which  completely  envelops 
it,  and  receives  the  name  of  the  hyaloid  7?iembrane.  Extend- 
ing anteriorly  through  the  midst  of  the  vitreous  mass,  from  the 
region  of  the  optic  disc  to  the  crystalline  lens,  is  a  minute 
canal,  lined  with  a  tube-like  prolongation  of  the  hyaloid 
membrane,  and  containing  a  watery  fluid.  This  is  termed 
the  hyaloid  ca?ial ;  it  represents  the  path  taken  by  a  branch  of 
the  arteria  centralis  retina,  which,  in  the  foetus,  extends  to  and 
supplies  the  capsule  of  the  lens,  but  afterwards  disappears. 

The  hyaloid  canal,  as  a  rule,  cannot  be  seen  in  an  ordinary  dissection 
of  the  eyeball ;  but  if  the  "  eye-kernel ""  be  shaken  up  in  the  picro-carmine 
solution  as  recommended  by  Anderson  Stuart,  it  may  sometimes  be  rendered 
evident  through  the  staining  fluid  entering  it.  It  is  represented  diagram- 
matically  in  Fig.  251. 

Zonula  Ciliaris  (O.T.  Zonula  of  Zinn).  Between  the 
corona  ciliaris  externally  and  the  margin  of  the  lens  internally 
lies  a  fibrous  membrane  called  the  zonula  ciliaris.  Its 
external  margin  is  attached  to  the  posterior  surfaces  of  the 
ciliary  processes  and  the  hyaloid  membrane,  and  its  internal 
margin  is  connected  with  the  lens.  As  it  approaches  the 
margin  of  the  crystalline  lens,  it  splits  into  two  parts,  viz.,  an 


BULBUS  OCULI 


exceedingly  delicate  deep  lamina,  which  lines  the  fossa 
hyaloidea,  and  a  more  superficial  stronger  part,  which  becomes 
attached  to  the  capsule  of  the  crystalline  lens. 

The  zonula  ciliaris  lies  subjacent  to  the  ciliary  processes, 
and  is  radially  plaited  or  wrinkled  in  correspondence  with 
these.  Thus  the  elevations  or  wrinkles  of  the  zonula  extend 
into  the  intervals  between  the  ciliary  processes,  whilst  the 
ciliary  processes  in  their  turn  lie  in  the  depressions  between 
the  wrinkles  of  the  zonula.  When  the  eye  is  fresh,  these 
opposing  parts  are  closely  adherent. 

The  zonula  ciliaris  is  strengthened  by  radially  directed 
elastic  fibres,  and  after  the   delicate   membrane  which  lines 


Retina 


/Sclera 

-Perichoi'ioidal  space 


Ciliary  muscle  (radiating  fibres) 

Ciliary  muscle  (circular  fibres) 
Sinus  venosus  sclera 

Spatia  anguli  iridis 
Ciliary  process 
Spatia  zonularia 
Suspensory  ligament 

Iris 


Fig.  256. — Diagrammatic  representation  of  the  Ciliary  Region, 
as  seen  in  vertical  section. 


the  fossa  hyaloidea  is  given  off  from  its  deep  surface,  it 
extends  inwards  as  a  distinct  layer,  and  is  attached  to  the 
anterior  surface  of  the  capsule  of  the  lens  a  short  distance 
beyond  the  margin  of  that  body.  In  this  manner  the 
suspensory  ligament  of  the  lens  is  formed.  But  this  is  not 
the  only  attachment  of  the  suspensory  ligament.  Some 
scattered  fibres  are  attached  to  the  circumference  or  equator 
of  the  lens  (equatorial  fibres),  whilst  others  are  fixed  to  its 
posterior  surface  close  to  its  margin  (post-equatorial  fibres). 

In  this  way  the  crystalline  lens  is  firmly  held  in  its  place 
in  the  fossa  hyaloidea.  Further,  the  degree  of  tension  of  its 
suspensory  ligament  is  influenced  by  the  radiating  fibres  of 


LENS  583 

the  ciliary  muscle,  which  by  their  contraction  pull  upon  the 
ciliary  processes,  and  produce  relaxation  of  the  zonula 
ciliaris. 

Spatia  Zonularia  (O.T.  canal  of  Petit). — In  reality  the 
spatia  zonularia  constitute  a  more  or  less  continuous  circular 
lymph  space,  which  surrounds  the  circumference  of  the  lens. 
It  lies  between  the  anterior  and  posterior  layers  of  the 
suspensory  ligament  and  is  filled  with  a  watery  fluid. 

By  introducing  the  point  of  a  fine  blow-pipe  into  the  spatia  zonularis 
through  the  suspensory  ligament,  it  can  be  partially,  or,  perhaps,  com- 
pletely, inflated  with  air.     It  then  presents  a  sacculated  appearance. 

Dissection.- — The  crystalline  lens  may  be  removed  by  snipping  through 
the  suspensory  ligament  with  scissors. 

Lens  Crystallina. — The  crystalline  lens  is  a  biconvex, 
solid,  and  transparent  structure  which  lies  between  the  iris 
and  the  vitreous  body.  It  is  enclosed  within  a  glassy,  elastic 
capsule,  to  which  the  different  parts  of  the  zonula  ciliaris 
are  firmly  cemented,  and  it  presents  for  study  an  anterior 
surface,  a  posterior  surface,  and  a  circumference  or  equator. 

The  anterior  surface  is  not  so  highly  curved  as  the  posterior 
surface.  Its  central  part,  which  corresponds  with  the  pupillary 
aperture  of  the  iris,  looks  into  the  anterior  chamber  of  the 
eye.  Around  this  part  the  margin  of  the  pupillary  orifice  of 
the  iris  is  in  contact  with  the  lens,  whilst  nearer  the  equator 
the  anterior  surface  of  the  lens  is  separated  from  the  iris  by 
the  fluid  in  the  posterior  chamber  of  the  eyeball.  T\\&  posterior 
surface  of  the  lens  presents  a  higher  degree  of  curvature  than 
the  anterior  surface,  and  is  received  into  the  fossa  hyaloidea 
of  the  vitreous  body.  The  equator  ox  circumference  is  rounded. 
It  forms  one  of  the  boundaries  of  the  spatia  zonularia,  and 
the  manner  in  which  the  zonula  ciharis  is  attached  to  the 
capsule  In  this  vicinity  has  been  described  already. 

Faint  radiating  lines  may  be  seen  on  both  surfaces  of  the 
lens.  These  give  a  clue  to  the  structure  of  the  lens.  They 
indicate  the  planes  along  which  the  extremities  of  the  lens- 
fibres  come  into  apposition  with  each  other. 

The  capsule  of  the  lens  is  a  resistant  glassy  membrane, 
which  is  considerably  thicker  anteriorly  than  posteriorly. 

The  anterior  wall  of  the  capsule  may  now  be  divided  with  a  sharp  knife. 
A  little  pressure  will  cause  the  body  of  the  lens  to  escape  through  the 
opening.  The  stained  capsule  can  be  very  advantageously  studied  whilst 
floating  in  water. 


584  BULBUS  OCULI 

If  the  lens  body  is  compressed  between  the  finger  and  thumb,  it  will 
be  noted  that  the  outer  portion  or  cortical  part  is  soft,  whilst  the  central 
part  or  nucleus  is  distinctly  firmer.  When  the  lens  is  hardened  in  alcohol 
it  can  easily  be  proved  that  it  is  composed  of  numerous  concentrically 
arranged  laminae. 

Chambers  of  the  Eyeball. — The  anterior  chamber  of  the 
eyeball  is  the  space  between  the  cornea  anteriorly,  and  the 
iris  and  central  part  of  the  lens  posteriorly.  At  the  irido- 
corneal angle  it  is  bounded  by  the  ligamentum  pectinatum 
iridis,  and  there  the  aqueous  humour  which  fills  this  chamber 
finds  access  to  the  spatia  anguli  iridis. 

The  posterior  chamber  is  a  circular  space  or  interval  which 
is  bounded  anteriorly  by  the  posterior  surface  of  the  iris,  and 
posteriorly  by  the  circumferential  part  of  the  anterior  face  of 
the  lens.  Externally,  this  space  is  closed  by  the  thick  anterior 
projecting  ends  of  the  ciliary  processes.  It  also  is  filled  with 
aqueous  humour. 


INDEX. 


Accessory  parotid,  126,  127,  261 
Aditus  laryngis,  378,  408,  409 
Agger  nasi,  396 
Alae  of  thyreoid  cartilage,  414,  415, 

421,  423 
Alveus,  497 
Ampullae    of    semicircular    canals, 

567 
Amygdaloid  nucleus,  491,  494,  512, 

514 
Annular  ligament  of  Stapes,  557 
Ansa   hypoglossi,     146,    234,    243, 
244,  246 
subclavia,   Vieussenii,   239,   250, 
257,  258,  319 
Antihelix,  153 
Antitragus,  154 
Aorta,  10,  83 

arch,  23,  30,  32,  44,  78,  85,  89,  96, 
98,  100,  102,  103,  106,  247 
position  of,  85 
ascending,  39,  55,  83,  98 

position  of,  83 
descending  thoracic,  31,  44,   50, 
58,  77,  89,  98,  102,  104,  106, 
109,  III 
Aortic  groove  on  left  lung,  40 
cusp,  Sy 

great  sinus  of,  84 
orifice,  74,  83 

sinus  of  (Valsalva),  78,  80,  84,  87 
valve,  87 
Apertura  medialis  ventriculi  quarti, 

539 

tympanica  caniculi  chords,   551, 

Apex  columni  anterioris,  197 
Apical  gland,  434 
Apices  of  the  auricles,  55,  65,  76, 
84,  89,  98 


585 


Aponeurosis,  366 

bucco-pharyngeal,  366 

of  palate,  382 

pharyngeal,  373 

vertebral,  235,  236,  237 
Appendix  ventriculi,  412,  421 
Aquseductus  cerebri,  503,  505,  506, 

.509,  511 
vestibuli,  566 
Aqueous  humour,  571,  584 
Arachnoidea  encephali,  438,  439 

spinalis,  185 
Arachnoideal     granulations,      202, 

206,  442 
Arch  lateral  lumbo-costal,  109,  167 

glosso-palatine,  430,  431 
Arcus   glosso-palatinus,    368,    378, 
380,  381,  382,  430,  431 
parieto-occipitalis,  464,  471,  472, 

474 
pharyngo  -  palatinus,     368,     369, 

378,  380,  381,  382 
tarseus,  137,  342 
Area  acustica,  525 
Artery  or  Arteries,    alveolar,   an- 
terior superior,  386,  389 
alveolar  inferior,  270,    272,   278, 

279 
alveolar  posterior  superior,   270, 

271 
angular,   12S,  131 

of  external  maxillary,  344 
anonyma.     See  Innominate 
anterior  cerebral,  450,  447,  448 
branches  of — 
anterior  medial  frontal,  449 
antero-median,  449 
intermediate  medial  frontal,  449 
medial  orbital,  449 
posterior  medial  frontal,  449 


586 


INDEX 


Artery  or  Arteries — 

cerebral,  posterior,  210,  446,  447 
branches  of,  446 

communicating,  450 
aortic  intercostal,  7 
ascending    palatine,     299,     382, 

383 
auditory,  445 

auricular,  deep,  270 

posterior,    154,    156,   157,  262, 
281,  296,  301,  306,  307 

of  superficial  temporal,  262 
axillary,  161,  249 
basilar,  210,  443,  445,  52S 

auditory  branch  of,  215,  445 
basis  pedunculi,  501 
bronchial,  22,  42,  98,  100,  103 
buccinator,  267,  270 
bulbar,  445 
calcarine  (of  posterior  cerebral), 

447 
carotid,  common,  23,  25,  31,  35, 
49,  232,  239,  243,  244,  245, 
246,  251,  252,  355 
external,    232,   234,   245,   247, 
262,  263,  269,  281,  294,  296, 
301,  306,  310 
internal,  208,  218, 220, 232,  234, 
245,   263,    281,    294,   296, 
300,    303,    304,    306,    307, 
310,312,314,316,317,327, 

331,  332,  385,  442,  447 
branches  of,  332 
left,  86,  8S,  89,   96,  99,    106, 
234,  235,  255,  310,  313,  317, 
320,  323 
centralis  retinae,  342,  580 
cerebral,  middle,  450 
cerebral,      middle,       448,       449 
(branches  of) — 
antero-lateral  basal,  450 
ascending  parietal,  450 
frontal  lateral  orbital,  450 
ascending  frontal,  450 
inferior  lateral  frontal,  450 
parieto-temporal,  450 
temporal,  450 
cerebellar,  anterior  inferior,  445 
inferior  posterior,  444 
superior,  445,  446 
cervical,  ascending,  252 

deep,  251,  254 
cervical,  superficial,  162 
ciliary,  342 

posterior,  343,  573,  578,  579  ' 
anterior,  343,  573,  578,  579 


Artery  or  Arteries- 
long  (ciliary),  343,  573,  578,  579 
short  (ciliary),  573^.578 
communicating,  anterior,  448 

posterior,  447 
coronary  (of  heart),  right,  76,  78, 
85,87 
left,  76,  78,  85,  87 
costo-cervical,  15,  no,  173,  317, 

323 

branches  of,  251,  254,  257,  258 
crico-thyreoid,  229,  234,  297 

inferior,  267 
descending  branch  of  deep  cervi- 
cal, 251 
dorsalis  linguae,  291 

nasi,  344 
epigastric,  superior,  7,  9 
ethmoidal,  344,  402 

j50sterior,  344 

anterior,  344 
external  maxillary,  126,  128,  129, 
225,  232,233,  271,  280,281, 
282,  283,  284,  296,  297 

transverse,  127,  261,  262,  302 
frontal,  344 

of  ophthalmic,  156,  157,  302 
great  palatine,  402,  404,  406 
hyoid,  296 
incisor,  279 

inferior  labial  of  external  maxil- 
lary, 300 
infra-hyoid  of  supra-thyreoid,  232 
infra-orbital,  129,  386,  388 
innominate,  48,  85,  88,  96,  247 
intercostal,  7,  9 

aortic,  102,  104,  105,  109,  126 

anterior,  7,  9 

posterior,  no,  254 

superior,  251,  254,  257,  258 
labial,  inferior,  130 
lacrimal,  342 

laryngeal,  inferior,  257,  372,  413, 
421,  422 

superior,   232,   296,    372,    413, 
421,  422 
lateral  nasal,  131 
lingual,  231,  232,  233,  286,  291, 

292,  296,  297 
lumbar,  176 
mammary,  9 

internal,  7,  9,  15,  34,  251,  254, 
257,  258 
masseteric,  266,  270 
mastoid,  of  occipital,  232 

of  posterior  auricular,  245 


INDEX 


587 


Artery  or  Arteries — 

maxillary,  internal,  242,  262,  267, 

269,  272,  274,  294,  296,  301, 
402,  403,  405,  406 

mediastinal,  104 

of  the  medulla  spinalis,  193 
meningeal,  anterior,  220,  221,  344 

accessory,   212,  220,  221,  270, 

274,  333 
of  ascending  pharyngeal,  220, 

221,  304 
of  internal  maxillary,  220,  221 
middle,    202,    210,    212,    220, 

270,  274,  277,  293,  333 
of  occipital,  220,  221,  301 
of  vertebral,  220,  221,  356 

mental,  279,  300 
musculo-phrenic,  7,  9 
mylo-hyoid,  270,  278,  283     . 
nasal   branches   of  anterior    eth- 
moidal, 393 
of  posterior  ethmoidal,  393,  406 
posterior   (of  spheno-palatine), 

406 
posterior  of  the  septum,  392 
nutrient  of  skull  and"  diploe,  202 
occipital,  145,  149,  156,  157,  162, 
169,  170,  232,  239,  262,  296, 
300,  302,  303,  306 
descending  branch,  169, 171, 172 
meningeal  branch,  169,  171 
sterno-mastoid  branch,  316 
oesophageal,  103,  104,  253,  307 
ophthalmic,  220,  339,  341 
palatine,  ascending,  383 

of  ascending  pharyngeal,  304, 

383 
descending,  383,  405,  406 

of  dorsalis  linguae,  383 

of  lacrimal,  342 

of  ophthalmic,  342 

small,  406 
palpebral,  137,  342 
parieto  -  occipital     (of     posterior 

cerebral),  447 
perforating,  of  internal  mammary, 

.  4'  9 
pericardial,  104 
pericardiaco-phrenic,  50 
petrosal    of    middle    meningeal, 

301,  333 
pharyngeal,  253 

ascending,  232,  246,  296,  303, 

307,  406 
branches,  304 
canal,  artery  of,  485 


Artery  or  Arteries — 

pontine,  445 

posterior  auricular,  302 

cerebral,  457 

communicating,'  480 

occipital,  303 

of  septum,  406 
prevertebral  branches  of  ascending 

pharyngeal,  304 
profunda  cervicis,  172,  173,  175 

linguse,  290,  291 
pterygoid,  270 

canal,  artery  of,  405 
pulmonary,    10,   22,    30,   34,  38, 
44,   55,   70,  75,  78,  84,  85, 

90,  99 
right,  76,  84,  86,  98,  loi 

left,  76,  86,  99 
foetal  condition  of,  77 
relations     of    extra-pulmonary 

part,  99 
orifice  of,  83 
relations  of,  76 
topography  of,  76 
ranine,  434 
retinal,  581 
septal  of  the  nose,  131 
short  posterior  ciliary,  574 
spheno-palatine,  402,  405,  406 
spinal,  109,  176,    181,    182,    193, 
252 
neural  branches  of,  182 
pre-laminar  branches  of,  182 
post-central  branches  of,  182 
anterior,  445 
posterior,  443 
sterno-mastoid,  of  occipital,  231, 
233>  235,  239,  300,  308 
of  superior  thyreoid,  232,  235, 

239,  245,  296,  308 
of  transverse  scapular,  235,  239 
stylo-mastoid,  147,  151,  161,  274, 

307 
subclavian,  23,  25,  31,  32,  34,  35, 
235,  239,  246,  247,  254,  257, 

258,  309>  315,  323 
branches  of,  251 
left,  86,  88,  89,  100,  102,  106, 

250,  255 
right,  250 
subcostal,  104,  109 
subungual,  291,  292,  300 
submental,   282,   283,   284,    292, 

300 
superior  epigastric,  7,  9 
intercostal,  7,  109,  no 


588 


INDEX 


Artery  or  Arteries — 

superior  labial,  130,  393 

septal  branch  of,  393 
supra-hyoid  of  lingual,  232,  291 
supra-orbital,  156,  157 
temporal  of  posterior  cerebral,  447 
deep,  267,  270,  303 
middle,    262,    265,    266,    267, 

270,  302 
superficial,  127,  157,  261,  262, 
277,  294,  296,  301 
thoraco-acromial,  161 
thyreo  -  cervical,    106,    251,    252, 
253,  254,  309,  323 
ascending   cervical  branch   of, 

240 
inferior,    106,    235,    245,    246, 

251,  252,  255,  315,  321,  323 
superior,    229,    230,   232,    234, 

243,  246,  253,  296,  308,  321 
thyreoidea  ima,  49,  229,  320,  321 
tonsillar,  299 
tracheal,  253 
transversa  colli,    106,    145,    147, 

149,  161,  164,  239,  242,  251, 

252,  253,255,  323 
transverse  facial,  127 

scapular,    106,    145,    147,    149, 
161,  164,  225,  242,  251,  252, 

253,  255,  309,  323 
tympanic,  270,  274 
vertebral,    106,    175,     179,    180, 

214,  220,  246,  251,  252,  253, 

255,  257,  323,  353,  354,  355, 

442,  443 
zygomatico-orbital,  302 
Articulations.     See  Joints 
Ary-epiglottic  folds,  329,  408,  409, 

415,  418,  420,  421,  427 
Aryt^enoid  cartilages,  379,  420 
Atria   of  heart,   34,   65,   68.      See 

Heart 
Atrio-ventricular  apertures,  69,  71, 

73,  79,  83,  92 

bundle,  74,  83,  93 

fibrous  rings,  93 
Atrium  medii  nasi,  395 
Auditory  apparatus,  546 
Auditory  tube,  293,  299,  312,  375, 
376,  381,  382,  383,  384,  559 

bony  position,  559 

cartilage  of,  384 

cartilaginous  portion,  539 

levator  cushion  of,  384 

ossicles,  movements  of,  557 

parts  of,  384 


Auditory  tube — 

pharyngeal  orifice  of,  384 
Auricle,  153,  546 
cartilage  of,  270 

Back,  161 

blood-vessels,  170,  175 
nerves,  162,  173,  177 
Basal  ganglia,  512 
Basilar  sinus,  183,  216 
Basis  pedunculi,  508,  509,  510 
Biventral  lobule,  533 
Brachia  conjunctiva,  511,  545 

cerebelli,  529,  530 
Brachial  plexus,  151 
Brachium  pontis  cerebri,  458,  531 

conjunctiva  cerebelli,  512 
Brain.     Also  vol.  i.  p.  28 
basal  ganglia,  437,  512 
base,  437 
blood-vessels,  442 
cerebellum,  437 
cerebral  hemispheres,  459 
cerebrum,  459 
corpus  callosum,  479 
fornix,  496 

fourth  ventricle,  458,  520 
general  appearance,  437 
general     connexion     of    several 

parts,  458 
general  structure,  461 
lateral  ventricles,  458 
lobule  paracentral,  466 
lobe  frontal,  466-470 

lateral  surface  of,  466 
medial  surface  of,  469 
orbital  surface  of,  469 
limbic,  477-479 
occipital,  472-474 

lateral  surface  of,  474 
medial  surface  of,  474 
tentorial  surface  of,  474 
olfactory,  477-478 
parietal,  470-472 

lateral  surface  of,  471 
medial  surface  of,  470 
temporal,  475-477 
lateral  surface  of,  475 
opercular  surface  of,  475 
tentorial  surface  of,  476 
medulla  oblongata,  437 
meninges,  439 
mesencephalon,  506 
origin  of  nerves,  454 
parts  in    posterior   cranial  fossa, 
452 


INDEX 


589 


Brain — 

peduncles  of,  506,  508 

pons  Varolii,  437 

posterior  horn  of  ventricle,  473 

preservation  of,  437 

removal  from  cranium,  211,  217 

septum  pellucidum,  495 

thalami,  500 

third  ventricle,  503 

velum  interpositum,  498 
Bronchi,  10,  22,  38,  44,  70,  ^^^  97 

eparterial,  22,  76,  98 

hyparterial,  10,  38,  44,  70 

left,  '^'],  98,  103 

relations  of  intrapulmonary  part, 
98 

right,  84,  98,  loi 
Buccal  aponeurosis,  366 

glands,  366 

plexus,  277 
Bucco-pharyngeal  fascia,  366,  370 
Bulb, 

of  cornu,  490 

of  jugular  vein,  307,  350 

olfactory,  208 
Bulla  ethmoidalis  of  nose,  398 
Bundle,  atrio-ventricular,  74 
Bursa,  pharyngeal,  376 

Calamus  scriptorius,  537 

Calcar  avis,  473,  490 

Calcarine    fissure,    446,    465,    473. 

478,  490 
Canal  carotid,  385 

central,  of  spinal  medulla,  181 

of  modiolus,  568 
facial,    552,    561,   562,   563,   564, 

565 
for  tensor  tympani,  551 

hyaloid,  581 

lacrimal,  138,  140 

membranous,  569 

pharyngeal,  405 

pterygoid,  405 

semicircular,  561,  565 
lateral,  567 
posterior,  567 
superior,  567 

spiral,  of  modiolus,  568 
Canalis  reuniens,  569 
Canalis  facialis,  552,  561-565 
Canthi,  120 

Capitular  articulations,  112 
Capsule,  external,  450,  512,  519 

internal,  450,  512,  514,  518 

of  lens,  583 


Caput  columncX'  anterioris,  197 
Cardiac  notch,  53 

plexus,  deep,  65,  85,  89,  96,  99, 
100  ■ 
superficial,  33,  43,  65,  78,  85, 

revolution,  93 
Carotid  body,  247 
canal,  385 
gland,  294 
plexus,  318 
sheath,  235 

triangle,  226,  232,  233 
Cartilage,  arytenoid,  379,  408,  410, 

411,  414,  415,  416,  417,  418, 

419,  420,  421,  427 
corniculate,   408,  415,  416,  421, 

427 
cricoid,  230,  414,  415,  426 
cuneiform,  408,  415,  421,  428 
of  epiglottis,  422 
lateral  of  nose,  141 
alar  of  nose,  141 
minor  or  sesamoid  of  nose,  141 
nasal,  140 
of  pinna,  155 
sesamoid  of  larynx,  420 
triticsea,  414 
thyreoid,  229,  230,  414,  415,  421, 

423 
Cartilagines  corniculatoe,  422,  427 
Caruncula  lacrimalis,  120 
Cauda  equina,  190 
Caudate  nucleus,  444,  488,  489,  491, 

518 
Cavernous  plexus,  285,  331,  332,  386 

sinus,  209,  210 
Cavity  of  thorax,  i,  10 
Cavum  Meckelii,  212,  329 

oris,  365 

septi  pellucidi,  495,  496 

subarachnoideale,  185,  439 

subdurale,  185,  204 
Central  canal  of  spinal  medulla,  196 
of  medulla,  521 
of  modiolus,  568 

grey  matter  of  aqueduct,  505 
Central  lobe,  462 

lobule,  531 
Centre,  lower  visual,  508 
Centrum  ovale,  480 
Cerebellar  peduncles,  534 

superior,  535 
Cerebello-olivary  tract,  525 

-spinal  tract,  525 
Cerebellum,  437,  529 


590 


INDEX 


Cerebellum — 

arbor  vitas,  534 
brachia  conjunctiva,  535 
corpus  medullare,  534 
fissures,  529,  531 
hemispheres,  529 
lingula  of,  538 

lobes,  529,  531,  532,  533,  534 
lobules,  531,  533 

central,  529,  531 

linguli,  538 
lobus  noduli,  533 

Pyramidis,  534 

tuberis,  534 

uvulae,  533 
monticulus,  529 
notches,  529 
peduncles,  superior,  532 

brachia  pontis,  529 

inferior,  527 
surface  of,  inferior,  530 

superior,  535 
vallecula,  530 
vermis,  529 
Cerebral  cortex,  461 
hemispheres,  461 

basal  ganglia,  512 

borders,  459,  460 

corona  radiata,  519 

cortex,  461 

fissures,  462-479 

general  structure,  458 

grey  matter,  461 

gyri,  461,  462,  479 

internal  capsule,  518 

island  of  Reil,  477 

lobes,  462,  466,  470,  472,  475, 

477 

medullary  centre,  461 

orbital  area,  459 

poles,  465 

sulci,  461 

tentorial  area,  459 

ventricles,  483, 492, 496,  503-506 
Cerebrum,  459,  520 

anterior  commissure,  503,  519 
borders  of,  459 
corpus  callosum,  446,  497 
fornix,  488,  496,  499 
frontal  pole  of,  460 
hemispheres,  459 
inferior  surface,  459 
lateral  surface,  459 

ventricles,  483-492 
longitudinal  fissure,  439,  449 
massa  intermedia,  504 


Cerebrum — 

medial  surface,  459 
occipital  pole  of,  460 
orbital  area,  459 
pedunculi,  210,  212 
posterior  commissure,  503,  505 
septum  pellucidum,  449,  488 
temporal  pole  of,  460 
tentorial  area,  459 
thalamus,  447-450 
third  ventricle,  503-506 
transverse  fissure,  499 
tela  chorioidea,  442 
Ceruminous  glands,  548 
Cervical  fascia,  235 
ganglion,  inferior,  319 
middle,  318 
superior,  317,  318 
pleura,  248,  250,  257 
plexus,  151,  239,  240 

communicating  branches  of,  241 
muscular  branches,  241 
sympathetic,  245,  247,  252 
Cervix  columnse, 

anterioris,  197 
posterioris,  197 
Chambers  of  eyeball,  571,  584 
Cheeks,  366 
Chest.     See  Thorax 
Chiasma,  optic,  441 
Choanse,  374,  375,  377,  389 
Chondroglossus,  434 
Chorda  tympani,  564 
Chordae  tendineae,  73,  74,  79,  80 

Willisii,  206 
Chorioid,  571,  574 
coat,  574 

lamina  corporis  capillaris,  575 
plexuses,  497 
vasa  vorticosa,  575 
Chorioidal  fissure,  492,  493,  494 
Chyle,  105 
Ciliary  body,  571,  574 

circular  fibres  of,  576 
folds,  577 
ganglion,  338 
muscle,  576 
orbicularis  ciliaris,  576 
processes,  577 
radiating  fibres,  576 
zone,  579,  583 
Cingulum,  479 
Circular  sinus,  209,  217 

sulcus,  462,  463 
Circulus  arteriosus,  441,  443,  450 
iridis  major,  579 


INDEX 


591 


Circulus  iiidis  minor,  579 

tonsillaris,  311 
Cisterna  cerebello-medullaris,  440, 

.    53S. 

chiasmatis,  441,  443,  450 

chyli,  105 

interpeduncularis,  210,  441,  443, 
450 

pontis,  441 

subarachnoidales,  440 

venae  magnD2  cerebri,  442 
Claustrum,  512,  516,  517 
Clava,  526 
Clivus,  532 
Cochlea,  565,  567  _ 

canal    of,     medial     longitudinal, 
568 

cupola,  568 

duct  of  the,  569 

ganglion  spirale,  56S 

lamina  spiralis,  568 

membranous  cochlear  tube,  56S 

modiolus  of,  568 

canal,  medial  spiral  of,  568 

scala  vestibuli,  566 
Collateral  fissure,  461,  462,  465 
CoUiculus  facialis,  537 
CoUiculi  (of  lamina  quadrigem-ina), 

506 
Column  of  Burdach,  199 

of  Goll,  199 
Columns  of  grey  matter  of  cord,  197 

lateral  grey,  198 
Commissures,  anterior,  of  brain,  503, 

519 

posterior,  503,  505 
Commissures  of  cord,  195,  196 

palpebral,  119 
Conchae  of  ear,  153 

of  nose,  376,  377,  389,  395,  396, 
397,  399,  400,  401,  402,  403 
Conical  papillre,  432 
Conjunctiva,  120,  139 

fornix  conjunctivce,  120 

plica  semilunaris,  120 

caruncula  lacrimalis,  120 
Conns   arteriosus,    30,    39,  54,   70, 
72,  74,  ^?,,  84 

elasticus.  414,  415,  418,  419,  421 

medullaris,  187,  188 
Convolution.     See  Gyrus 
Cord,    gangliated,    of  sympathetic, 
2,  23,  25,  108,  109 

spinal.     See  Spinal  medulla 

vocal,  579,  581 
Cords  of  brachial  plexus,  151 


Cornea,  572,  573,  574,  579 
Corneo-scleral  junction,  573 
Cornu  Ammonis,  491,  492,  493,  497 
Cornua   of  lateral   ventricles,  487, 
490,  491,  492 

of  thyreoid  cartilage,  424 
Corona  ciliaris,  577 

radiata,  519,  578,  596 

radiator,  519 
Coronary  plexus,  65,  85 

sinus,  89 

sulcus,  68 

valve,  81 
Corpora  mamillaria,  452,  453,  497, 

503,  5.04 
quadrigemina,  210,  447,  500,  506, 

507,  511,  512,  529 
superior,  503,  506,  507 
brachia  of,  507 
geniculatum,  512 
Corpus   callosum,    446,  458,   473, 
478,  479,  480,  48 1,  488,  490, 

495>  496,  497,  498,  499 
central  part,  494 
fibres,  481,  483 
genu,  448,  478,  482,  483,  487, 

495 

lamina  rostralis,  of,  482 
rostrum,  448,  449,  482,  483 
radiation,  483 
truncus  of,  482,  487 
splenium,  446,  478,  482,  483, 
486,  494,  495,  499 
Corpus  geniculatum  external,  503 
internal,  507 
laterale,  507,  508 
mediale,  506,  507 
Corpus  mamillare,  519 
striatum,  512,  515 
trapezoidum,  545 
Costo-mediastinal  sinus, 
-transverse  joints,  113 

ligaments  of  the  tubercles, 
-vertebral  articulations,  112 
Cranial  fossa,  middle,  325,  2)2>3 
Crescentic  lobule,  531,  532 
Cricoid  cartilage,  230,  414,  415,  426 
Crico-thyreoid  membrane,  297,  415 
Crista  vestibuli,  566 
Crura  of  crucial  ligament,  '^6], 
Crura  of  stapes,  557 
Crus  helicis,  153 
Crus  laterale  of  malleus,  555 

of  incus,  555 
Crystalline  lens,  571,  578,  581,  5S3 
Ciilmen  monticuli,  530,  531 


12,  16,  25 


m 


592 


INDEX 


Cuneate  funiculus,  540,  541 

nucleus,  541 

tubercle,  379 
Cuneiform  cartilage,  408,  415,  421 

tubercle,  379 
Cuneus,  447,  473 
Cupola  modioli,  568 

Decussation  of  the  lemniscus,  542 

motor,  542 

of  pyramids,  542 

sensory,  542 
Declive  Monticuli,  531 
Dentate     fascia,     479,    483,     492, 

495 
fissure,  479,  495 
nucleus  of  cerebellum,  539 
Diaphragm,  3,  35,  50,  70,  88,  99, 
100,  102,  103,  105,  241 
central  tendon  of,  88 
crura  of  104,  105,  iii 
membranous  cervical,  36 
Diaphragma  oris,  284 

sellffi,  209 
Diaphragmatic  line  of  pleural  reflec- 
tion,  14,  17,  18,  19 
pleura,  16 
Digastric  triangle,  226 
Dilatator  pupillee,  578 
Diencephalon,  520 
Disc,  intervertebral,  357 

optic,  580,  581 
Discus  articularis  of  jaw-joint,  268, 

271,  272,  273,  274 
Dissections — Thorax — 
thoracic  wall,  3,  4,  7 
thoracic  cavity,  12,  25,  29,  32, 

33.  43>  46,  48 
pericardium  and  heart,  49,  51, 

60,  65,    76,  78,   79,  87,  88, 

89,  91 
deep   of  the  thorax,    98,   lOi, 

104,  109 
thoracic  joints,  112 
Head  and  Neck — 

face,   117,  120,   126,   128,   132, 

133,  134,  140 
posterior  triangle  of  neck,  142, 

I43>  145'  146 
scalp,  153,  154,  158,  159 
sterno-clavicular  joint,  159 
back,  161,   162,   164,  166,  167, 

168,  171,  172,  176,  178,  179, 

181,  185,  191,  192,  200 
removal  of  the  brain,  200,  203, 

207,  211,  217,  222 


Dissections — Head  and  Neck — 

anterior  part  of  neck,  223,  225, 
229,  230,231,  234,  238,  239, 

244,  261,  262,  303,  304,  309, 
310,  317,  324,  325 

temporal     and     infratemporal 

regions,  266,  274,  279,  293 
submaxillary  region,  279,  282, 

284 
great    vessels    and    nerves    of 

neck,  303,  304,  309,  324 
lateral   part  of  middle   cranial 

fossa,  325,  329 
orbit,  334,   335,  339,  346,  348, 

350 
prevertebral  region,   350,    353, 

356 
joints  of  neck,  358,  361,  362, 363 
maxillary  nerve,  386 
pharynx,   369,   370,    372,    374, 

376,  381,  382 
nasal  cavities,    389,    393,   397, 

398,  399 
spheno-palatine  ganglion,  402, 

405 
larynx,  413,  415,  417,  419,  421, 

422 
brain,  457,  460,  479,  480,  483, 

484,  485^  490,  494,  495,  496, 
498,  500,  505,  512,  519,  528, 

536,  539,  540 
auditory  apparatus,    546,    549, 

559 
intrapetrous    portion    of  facial 

nerve,  562,  565 
eyeball,    570,    572,    575,    576, 

579,  581,  583 
Duct,    lymphatic,    right,    48,    242, 

245,  255 
naso-lacrimal,  120,  140,  346,  399 
of  Cuvier  (foetal),  91 

parotid,  126 

sublingual,  289 

sub-maxillary,  288 

thoracic,  2,   18,  31,  32,  48,  49, 
70,  87,   102,   104,   106,  108, 
III,  242,  245,  255 
Ductus  arteriosus,  33,  77,  78 

cochlearis,  569 

endolymphaticus,  569 
Dura  mater  encephali,  201 

layers  of,  202,  203 

partitions,  203 

sinuses,   162,  202,  205,  207,  211, 
217 

spinalis,  183 


INDEX 


593 


Ear,  547 

annulus  tympanicus,  549 

concha  of,  546,  547 

external,  546 

internal  or  labyrinth,  546,  565 

mastoid  ear  cells,  550 

meatus  -  external      acustic,     546, 

547,    548,    549,    550,    559, 
560,  561 
membrana    tympani,     547,     548, 

549,  553,  554,  555,  561 
middle  ear,  546,  550 
tragus  of,  547 
tympanic  cavity,  546,  550 
tympanic  antrum,  550,  551,  554, 

555,  559,  560,  561 
tympanic    membrane,    umbo   of, 

549 
Ecto-rhinal  fissure,  465,  475 
Elastic  lamina  of  cornea,  574 
Eminence,  olivary,  524,  525,  526 
Eminentia  collateralis,  anterior,  494 

posterior,  494 
Endocardium,  92 
Endolymph,  546,  566 
Eparterial  bronchus,  22,  'j6,  98 
Ependyma,  485,  526 
Epicardium,  92 
Epicranial   aponeurosis,    122,    123, 

154,  156,  158 
Epiglottis,  379,  408,  409,  423 
action  of,  429 
cartilage,  422 
frenum,  409 
petiolus  of,  423 
tubercle  of,  409 
Ethmoidal  cells,  395 
Eustachian  orifice,   293,   299,  312, 
375,  376,  381,  382,  383,  384 
tube,  293 
Excavatio  papillae,  580 
Eyeball,  570 

bulbus  oculi,  570 
chambers,  571,  584 
anterior,  585 
posterior,  585 
equator,  570,  572 
general  structure  of,  571 
meridional  lines,  570 
poles,  570 

refracting  media,  571 
sagittal  axis,  570 
tunics,  571 
Eyebrows,  118 
"Eye-kernel,"  581 
Eyelids,  119,  134 

VOL,  11—33 


Eyelids,  conjunctiva,  119 
glands,  132 
ligaments,  121 
tarsi,  134 
vessels  and  nerves,  137 

Face,  117 

arteries,  128 
muscles,  120 
nerves,  126 
surface  anatomy,  117 
Falciform  lobe,  465,  481 
Falx  cerebelli,  212,  215,  529 
Fascia,  axillary,  147 

buccinator,  261 

bucco-pharyngeal,  366,  370 

bulbi,  347-350 

carotid  sheath,  235,  236,  238 

cerebri,  206,  459 

cenncal,  145,  224,  225,  235 

deep  cervical,  235 

deep  of  posterior  triangle,  144 

dentate,  479,  483,  492,  495 

intra- thoracic,  12 

lumbo-dorsal,  166,  167 

palpebral,  135 

parotid,  126 

peri-renal,  168 

pharyngo-basilar,  373 

pretracheal,   229,  230,   235,  236, 

237 
prevertebral,  235,  236,  237 

of  Sibson,  36 
submaxillary,  226 
superficial  cervical,  235 
temporal,  265,  266 
Fasciculus    cerebro  -  spinalis,     510, 

519,  527 
cerebello-spinalis,  200 
anterior,  200 
lateralis,  200,  542 
Fasciculus  cuneatus,  199,  200 
gracilis,  199,  200 
thalamo-mamillaris,  447 
Fasciola  cinerea,  483 
Fauces,  isthmus  of,  365,  368 

pillars,  368 
Fenestra  cochleae,  552,  561,  568 
vestibuli,  552,  557,  561,  562,  564, 
566 
Fibrae  arcuatoe,  528 
Filum  terminale,  183,  187,  188 
Fimbria,  479,  491,  492,  494 
Fissure  or  Fissures,  calcarine,  446, 
461,  465,  473,  478,  490 
central,  462,  464 


594 


INDEX 


Fissure  or  Fissures — 

of  cerebellum,  529,  531 
of  cerebrum,  462,  479 
chorioid,  492,  493,  494 
collateral,  461,  462,  465,  474,  475, 

476,  479,  499 
dentate,  479 
ecto-rhinal,  465,  475 
great  horizontal,  530 

longitudinal,  439,  449,  460 
transverse  of  brain,  492 
hippocampal,  461,  465,  495 
lateral  of  brain,  451,   459,   462, 
463,  466,  476 
anterior  ascending  limb,  463 
anterior  horizontal  limb,  463 
posterior  ramus,  463 
longitudinal    of  brain,   437,  439, 
449,  460 
'    of  lung,  41 
of  medulla,  195 
oral,  365 
palpebral,  119 

parieto-occipital,  448,  462,  464 
lateral,  464,  470,  473,  480 
medial,  464 
of  spinal  medulla,  195 
transverse  of  brain,  499 
Foetal  circulation,  68,  69,  77 
Fold,  ary-epiglottic,  379,  408,  409, 
415,  418,  420,  421,  427 
glosso-epiglottic,  409,  423,  430 
pharyngo-epiglottic,  409,  423 
salpingo-pharyngeal,  376 
tympano-malleolar,  549 
anterior,  549,  554 
posterior,  549,  554 
ventricular.     See  Plicae 
vestigial,  91 
vocal.     See  Plicae 
Folium  vermis,  530 
Fontana,  spaces  of,  574 
Foramen  caecum  of  medulla  oblon- 
gata, 521 
caecum  of  tongue,  430 
interventriculare,  459,  486,   489, 

502,  505 
of  Magendie,  539 
ovale,  68,  78,  92 
Foramina    venae    minimae    cordis, 

92 
Forceps     major,     483,     490,     494, 
496 
minor,  483 
Formatio  alba,  543 
grisea,  543 


Formatio  reticularis,  510,  543,  545 
Fornix,  488,  492,  495,  496,  499 

body,  496,  497,  498,  499 

columns  of,  485,  497 

of  conjunctiva,  119 

crura  of,  496,  497,  498 

transverse  fibres  of,  497 
Fossa  of  antihelix,  154 

cranial,  middle,  325,  333 

of  helix,  154 

hyaloidea,  581,  582,  583 

interpeduncularis,  452,  503 

nasal,  393 

ovalis,  68,  69,  92 

pterygo-palatine,  386,  388 

recessus,  379 

rhomboidalis,  536,  537 

scaphoid  of  ear,  154 

supraclavicularis,  major,  142 
minor,  142 

supra-sternal,  178 

supra-tonsillar,  378 

triangular  of  ear,  1 54 
Fourth  ventricle,  536 

ala  cinerea,  538 

area  acustica,  538 

area  postrema,  538 

colliculus  facialis,  538 

eminentia  medialis,  537 

floor,  536 

fovea  superior,  538 

funiculus  separans,  538 

lateral  recesses,  536 

medullary  striae,  538 

plexus  chorioid,  539 

roof  of,  536,  538 _ 

substantia  ferruginea,  538 

tuberculum  acusticum,  538 
Fovea  centralis  retinae,  580 

inferior,  538 

recessus  ellipticus,  566 
recessus  sphaericus,  566 

superior,  538 
Frenulum  of  Giacomini,  495 

of  lips,  133,  365 

veli,  506 
Frenum  of  epiglottis,  409 

linguae,  288,  292,  368 
Frontal  lobe,  449,  462 

operculum,  463 

pole,  465 

region  of  head,  117 

sinus,  396,  397 
Fronto-parietal  operculum,  463,  475 
Fungiform  papillae,  432 
Funiculus  anterior,  199,  200 


INDEX 


595 


Funiculus — 

gracilis,  540,  541 
lateral,  199,  200 
posterior,  199,  200 
Furrowed  band,  533 

Galea  aponeurotica,   122,  123,  154, 

156,  158 
Gangliated  cord  of  sympathetic,  2, 

23,  26,  108,  109 
Ganglion,  basal,  512 
cervical,  inferior,  355 
middle,  318 

superius  of  glosso-pharyngeal, 
312 
ciliary,  332,  339,  341,  386,  578 
long  root  of,  340 
short  roots  of,  34 
coeliac,  28 

communications  of,  313 
first  thoracic  sympathetic,  1 10, 254 
geniculi  of  facial,  312,  332,  333, 

562,  563,  564 
jugulare  of  vagus,  312,  313 
nasal  branches  of,  393 
nodosum  of  vagus,  313,  314,  315, 

.316,  317 
orbital  branches  of,  405 
otic,  276,  277,  279,  293,  383,  559 
petrosum    of    glosso-pharyngeal, 

312,  313.  317 
semilunar,    211,    212,    275,    326, 
328,  329,  332,  333,  385,  386 
spheno-palatine,    386,    388,    392, 

393,  402,  403,  404,  405 
spinal,  189 
spirale,  568 
splanchnic,  28 

submaxillary,  282,  284,  285,  318 
inferior  cervical  sympathetic,  317, 

319 
middle  cervical  sympathetic,  318, 

319 

superior     cervical     sympathetic, 
312,  314,  317,  3S5 

superius,  ofglosso-pharyngeal,  312 
of  vagus,  313,  315 
Geniculate  bodies,  507 
Genu  of  corpus  callosum,  448,  478 

of  internal  capsule,  518 
Giacomini,  frenulum  of,  495 
Glabella,  118 
Gland,  buccal,  366 

carotid,  305,  306 

labial,  365 

lacrimal,  138,  334,  336,  337 


Gland,  lacrimal  inferior,  337 
superior,  337 
molar,  366 

mucous  of  soft  palate,  380 
sublingual,  368 
ducts  of,  368 
submaxillary,  225,  226,  368 
thyreoid,  407 
lateral  lobe,  407 
pyramidal  lobe,  407 
Globus  pallidus,  516 
Glosso-epiglottic  folds,  409,  423,  430 
Glottis,  true,  410 

pars  intercartilaginea,  411 
pars  intermembranacea,  411 
vocalis,  407,  410 
Goll,  column  of,  199 
Gracile  funiculus,  540,  541 
lobule,  534 
nucleus,  541 
Granulationes  Arachnoideales,  202, 

206 
Grey  commissure,  195,  196 

matter  of  the  medulla  spinalis, 
196 
Groove,  aortic  on  left  lung,  40 
coronary,  53,  57,  71,  89,  91 
interventricular,  53,  63,  71 
Gullet,  2,  10,  17,  23,  26,  29,  30,  31, 
32,  39,  40,  49,  50,  58,  85,  87, 
89,  96,  99,  100,  loi,  103,  106 
Gums,  367 

Gyrus  or  Gyri,  461,  462,  479 
angular,  472,  475 
callosal,  479 

central  anterior,  450,  467 
inferior,  467,  468- 
middle,  467 
superior,  467 
cinguli,  466,  471,  478,  479,  481 

posterior,  472 
cunei,  447,  473 

cuneo-lingual,  anterior  deep,  473 
dentatus,  479,  483,  491,  495 
fornicatus,  473,  478,  480 
of  frontal  lobe,  450 
frontal,  450 
inferior,  469 
middle,  466 
superior,  466,  469 
fusiformis,  474,  476 
hippocampal,  446,  447,  465,  474, 

475,    47S,    479,    494,    495, 
508 
opercuia,  469 
anterior,  470 


596 


INDEX 


Gyrus  or  Gyri — 

opercula  medial,  470 

orbital,  450 

parietal,  450,  469 

posterior,  472 
pars  basilaris,  469 

orbitalis,  469 

triangularis,  469 
post-central,  450 

-parietal,  472,  475 
rectus,  469 

sub-callosus,  478,  483 
supra-callosus,  482 
supra-marginal,  472 
•    temporal,  450 

inferior  472,  474,  476,  477 

middle,  476 

superior,  471,  476 

Habenula,  502 

commissure  of,  502 
trigonum  of,  502 
Head  and  Neck,  117 
auditory  apparatus,  546 
base  of  brain,  452 
brain,  200 

(encephalon),  437 
carotid  canal,  385 
cranial  cavity,  200 
eyeball,  570 
face,  117 

frontal  region  of  head,  117 
intrapetrous    part    of    the    facial 

nerve,  546 
infra-temporal  region,  265 
joints,  356 
larynx,  406,  410 

lateral    part    of    middle    cranial 
fossa,  325 

structures  in,  325 
maxillary  nerve,  386 
mouth  and  pharynx,  364 
movements,  364 
nasal  fossae,  393 

cavities,  389 
neck,  142,  222 
orbit,  333 

contents  of,  333,  334 
prevertebral  region,  350 

structures  in,  350 
scalp,  152 
submaxillary  region,  279 

structures  contained  in,  279 
temporal  region,  152,  265 
Heart,  22 
action,  93 


Heart — 

anterior   longitudinal  sulcus,    53, 

.63,  71 
aortic  orifice,  79,  81 
position  of,  81,  87 
valve,  81 
cusps  of,  81 
apex,  53,  55,  56 

atrio-ventricular  orifices,  69,   71, 
73'  79,  83,  92 
bundle,  74,  S^,  93 
position  of,  87 
rings,  93 
atrium,   30,  34,   53,   54,   65,   68, 
74,  76,  89 
dextrtim,  65,  66,  68,  74 
sinistrtim,  68,  76,  84,  89,  102, 
104 
position,  89 
orifices  of,  92 
atrio-ventricular  fibrous  rings,  93 
fibres  of  atria.  92 
auricles,  55,  65,  ^6,  84,  89,  98 
base,  59 

bicuspid  valve  (mitral),  80 
border,  left,  55 
right,  55 
chordae  tendineae,  73,  74,  79,  80 
conus  arteriosus,  30,  39,  54,  70, 

72,  74,  78,  84 
coronary  sinus,  68 

sulcus,  53,  57,  71,  89,  91 
valve  of,  69 
crista  terminalis,  65,  66 
endocardium,  92 
epicardium,  92 
external  form,  53 
foramen  ovale,  68 
foramina    venae   minim ae    cordis, 

64,  69,  92 
fossa  ovalis,  6?>,  69 
general  relations,  50 
great  sinus  of  aorta,  84 
incisura  cordis,  53,  57 
inferior  longitudinal  surface,  58 
interatrial  sulcus,  89 
limbus  fossae  ovalis,  67,  69 
mitral  valve,  80,  92 
moderator  band,  71,  74 
musculi  papillares,  73,  79,  80 

pectinati,  66,  91 
myocardium,  92 
nerves,  33,  43,  65,  78,  85,  ?,T,  89, 

96,  99,  100 
orifices,  topography  of  great,  87 
pars  membranacea  septi,  74,  83 


INDEX 


597 


Heart — 

pulmonary  orifice,  71,  72 

cusps  of  valve,  75 
lunulce  of  the  valve,  75 
nodules  of  the  valve,  75 
sinus,  75 

topography  of,  75,  S7 
valve,  75,  78 
semilunar  valves,  73,  78,  81 
septum  atriorum,  69 

ventriculorum,  71,  72,  78,  82 
sinus  venosus,  34,  54)  66 
sulcus  anterior  inter- ventricular ,  7 1 

terminalis,  34,  54,  63 
supra-ventricular  ridge,  72 
surfaces,  53,  56,  58 
diaphragmatic,  58 
sternocostal,  53,  56 
topography,  57,  75,  94 
trabecule  carnese,  72,  79 
tricuspid  valve,  66,  73,  83 

cusps  of,  73 
tubercle,  intervenous  (Lower),  67 
valve  of  the  coronary  sinus,  69 
valve    of    the    vena    cava    (Eus- 
tachian), 67 
ventricle,  left,  79 
cavity,  79 

fibres  of  the  ventricles,  93 
ventricle,  right,  70,  74 
atrio-ventricular  orifice,  71 
cavity,  72 

conus  arteriosus,  72 
ventricles,  34,  53,  55,  70,  74,  79 
vessels,  63,  64,  76,  78,  85,  87 
wall,  92 
Helicotrema,  568 
Helix,  158 
crus,  153 
fossa,  154 

processus  caudatus,  155 
spine,  155 
Hemisphere,  cerebellar,  529 

cerebral.       See    Cerebral    hemi- 
spheres 
Heschl,  sulci  of,  475 
Hiatus  semilunaris  of  nose,  397,  398 
Hippocampus,  491,  492,  493,  497 
digitations,  491 
minor,  494 
pes,  491 
taenia,  442,  447 
Horner,  muscle  of,  121 
Hyaloid  canal,  581 

membrane,  581 
Hyparterial  bronchi,  10,  38,  44,  70 


Hypophysis  cerebri,   208,  209,  218, 
222,  439 

Incisive  bundle,  123,  133 

pad,  133 
Incisura  cardiaca,  53 

intertragica,  154 

temporalis,  465,  475 

thyreoidea,  423 
Incus,  556,  557 

body,  556 

crus,  long,  536 
short,  557 

processus  anticularis,  557 
Inferior  corpus  quadrigeminum,  530 
Infra-orbital  plexus,  128,  129,  389 
Infundibulum    of  brain,   208,   218, 

453 
of  hypophysis,  505 

of  nose,  397 
Insula,  450,   475,   476,    477,   49°. 
578 
opercula  of,  477 
Interarticular  meniscus,  113 
Interatrial  sulcus,  89 
Intercavernous  sinuses,  326 
Inter-chondral  articulations,  113 
Intercostal  membranes,  4,  108,  109 
Internal  acustic  meatus,  566 
capsule,  501,  515,  516,  518 
anterior  limb,  518 
connections  of,  518,  519 
genu,  518 
posterior  limb,  518 
ear,  546,  565 
Interpeduncular  fossa,  452 
Intervertebral  fibro-cartilages,  112 
Intumescentia  cervicalis,  187 
lumbalis,  187 
Iris,  571,  574,  576,  577,  578,  579 
Island  of  Reil,  477 
Isthmus  of  auditory  meatus,  548 
of  auditory  tube,  384 
of  fauces,  368,  369,  378 
of  gyrus  cinguH,  478,  479 

fornicatus,  478 
of  limbic  lobe,  478 
of  pharynx,  376,  377 
of  thyreoid  gland,  229,  320 
of  rhombencephalon,  536 

Jacobson's  nerve,  312,  563 
Joints,  atlanto-epistropheal,  362 

atlanto-occipital,  361 

capitular,  113 

costo-transverse,  113 


598 


INDEX 


Joints — 

cervical,  356,  357 

costo-vertebral,  113 

crico-arytaenoid,  428 

crico-thyreoid,  425 

inter  chondral,  113 

intervertebral,  115 

manubrio-gladiolar,  112 

sterno-chondral,  iii 

sterno-clavicular,    49,    159.      See 
also  vol.  i.  pp.  28,  245 

temporo-mandibular,     262,     268, 
271 
movements  of,  273 
muscles  of,  274 
synovial  stratum  of,  273 

of  thorax,  112 
Jugular  ganglion  of  vagus,  313 

Labial  glands,  365 
Labyrinth,  552,  561,  565,  566,  567, 
568,  569 
membranous,  565,  569 
osseous,  565 
Lacrimal  apparatus,  138 
Lacrimal  ducts,  119,  138,  140 
gland,  138,  337 
sac,  136,  140 
superior,  337 
inferior,  337 
Lacunas  laterales,  206 
Lacus  lacrimalis,  119,  139 
Lamina  terminalis,  448,  449,  454, 

503     .       . 

chorio-capilldris,  568 

cribrosa  of  eye,  572 

fusca,  572 

posterior  elastic  of  cornea,  574 

quadrigemina,  459,  506 

spiralis,  568 
Laminae,  medullary,  576 
Larynx,  406,  410 

aditus  laryngis,  378,  408,  409 

cartilages,  422,  423,  426,  427 

general  construction,  407 

glottis,  410 

interior,  407 

mucous  membrane,  413 

position,  407 

superior  aperture,  408 

ventricles  of,  412 

vestibule,  407 

vocal  cords,  410 
Lateral   Recesses    of   fourth   ven- 
tricle, 536 
of  pharynx,  376 


Lateral    sulcus   of  mesencephalon, 

506 
Lateral  Ventricles,  485,  502 
anterior  horns  of,  485,  487 
central  part  of,  485,  487 
cornua,  487,  490 
ependyma  of,  485 

inferior  horns   of,   483,  484, 

485,  487,  490,  491 
posterior  horns  of,  483,  484, 
485,  486,  487,  490 
pars  centralis,  488 
Lemniscus,  512,  545 
internal,  544 
lateral,  512,  545 
medial,  512,  528,  545 
Lens,  583 

capsule  of,  582,  583 
cortical  part  of,  584 
nucleus  of,  584 
suspensory  ligament,  582,  583 
Lenticular  ganglion,  332 
Lentiform  nucleus,  514,   515,    517, 

■518 
Levator  palati,  547 
Ligaments,  accessory  atlanto-epis- 
tropheal,  362 
alar  epistropheal,  364 
alaria,  364 
anterior    costo  -  transverse,     109, 

115 

anterior   longitudinal,    115,    357, 

apicis  dentis,  363 

atlanto-epistropheal,  362,  363 

atlanto-occipital  capsular,  361 

of  auditory  ossicles,  557 

auricular,  154 

capitular,  112 

connecting     atlas,     epistropheus, 

and  occipital  bone,  360 
.    cruciatum    transversum    atlantis, 

362 
crico-thyreoid,  229,  230,  297 
crico-tracheal,  427 
cruciatum,  362,  363 
crus  superius  of,  363 

inferius,  363,  41 3^  4^5 
epiglottidean,  423 
of  epiglottis,  423 
flava,  181,  358,  360 
hyo-epiglottic,  423 
ilio-lumbar,  168 
of  incus,  557 
interspinous,  359 
intertransverse,  116,  359 


INDEX 


599 


Ligaments — 

intervertebral,  Ii6 

fibro-cartilage,  ii6 

annulus  fibrosus,  Ii6 

nucleus  pulposus,  Ii6 
of  malleus,  anterior,  557 

of  incus,  557 

lateral,  557 

superior,  557 
medial  palpebral,    121,  134,  136, 

140,  337 
of  neck  of  rib,  114 
oblique  of  atlas,  181 
occipito-atlantal,  362,  363 
of  pinna,  153 
pterygo-mandibular,  463 
pulmonary,  14,  16,  35,  43,  70 
posterior  costo-transverse,  115 
posterior  longitudinal,    116,   182, 

357 
of  stapes,  557 
radiate,  113 
sacro-tuberous,  178 
spheno  -  mandibular,     268,     269, 

270,  271,  272,  277,  278 
sterno-chondral,  113 
sterno-clavicular,  243 
sterno-costal  radiate,  113 
sterno-pericardiac,  50 
stylo-hyoid,  286, 287, 290,  292,296 
stylo-mandibular,  237,  263,  271, 

272,  282 
supraspinous,  166,  173,  181,  359 
suspensory,  of  axis,  363 

of  lens,  583 

of  orbit,  349 

of  Lockwood,  349 

of  eyelids,  palpebral,  121 
temporo-mandibular,     271,    272, 

273  . 
thyreo-epiglottic,  408,  420,  423 
thyreo-hyoid,  median,  413 
lateral,  413,  414 
of  the  neck  of  the  rib,  115 
transverse,  of  atlas,  362 

of  the  tubercles,  114 
upper  transverse  of  scapula,  164, 

242 
vocale,  415,  418,  419,  420,  428 
Ligamentum    arteriosum,   33,    77, 
78,  85,  87,  89,  100 
denticulatum,  186,  188,  214,  215, 

220,  355 
pulmonis,  14,  16,  35,  43 
nuchae,  172 
pectinatum  iridis,  574,  584 


Ligamentum       ventriculare,      410, 

420 
Ligamenta  flava,  181,  358,  360 
Ligula,  531 
Limbic  lobe,  478 
Limbus  fossce  ovalis,  67 
Linea  splendens,  186,  188 
Lines  of  pleural  reflection,   14,   17, 

18,  19 
Lingual  glands,  283,  434 
Lingula,  529,  535 
Lips,  365,  366 
Liver,  caudate  lobe  of,  104 
Lobe  or  Lobes,  of  cerebellum  under 
surface,  533 

central,  of  cerebellum,  531 
of  cerebrum,  462 
alae  of,  532 

cerebellar,  531 

cerebral,  462 

culmen  monticuli,  532 

culminis,  532 

of  clivus,  532 

of  culmen,  532 

frontal,  449,  462 

insular,  462 

limbic,  478 
Lobus  tuberis,  534 

culminis  cerebelli,  532 

clivi,  532 

declive  monticuli,  532 
posterior  crescentic  lobule,  532 

folium  vermis,  532 

gracilis,  534 

semilunaris  superior,  532 
Lobe  or  Lobes,  of  lung,  41 

of  nodulus,  533 

occipital,  450,  462 

olfactory,  462 

parietal,  450,  462 

of  pyramid,  534 

pyramidal,  of  thyreoid  gland,  321 

substantia  perforata  anterior,  462 

semilunar  superior,  532  ' 

temporal,  450,  462 

of  tuber,  534 

of  uvula,  534 
Lobule      or      Lobules,      biventral, 

5-^  -> 
JO 

central,  of  cerebellum,  531 
crescentic,  anterior,  531,  532 

posterior,  531,  532 
of  ear,  153 
gracile,  534 
paracentral,  449 
parietal,  450 


6oo 


INDEX 


Lobule  or  Lobules — 

parietal  inferior,  471,  472 
superior,  471,  472 

posterior  superior,  531 

quadrate,  532 
Locus  coeruleus,  537,  545 
Longitudinal  bundle,  medial,  511 

sagittal,  inferior,  217 
superior,  207 
Lumbo-dorsal  fascia,  166,  167,  168 
Lung,  17,  35 

aortic  groove,  40 

apex,  17,  36 

azygos  groove,  40 

base,  36,  37 

borders,  36 

bronchi,  22 

differences  between  right  and  left, 

fissures,  41 

hilus,  38,  40,  44 

incisura  cardiaca,  42 

innominate  groove,  40 

ligamentum  pulmonis,  35 

lobes,  41 

pedicle,  14,  42,  43 

root,  42,  43 

subclavian  groove,  36,  40 

surfaces,  36,  37 

sulci,  40,  42 

weight,  35 
Lunulse,  75 

Lymph  duct,  right,  48,  107 
Lymph  glands,  apical   of  tongue, 

434 
bronchial,  22,  43,  108 
buccal,  133 
cervical,  146 

upper  deep,  232,  261,  308 
intercostal,  108,  256 
mastoid,  154,  158 
mediastinal,  10,  89 

anterior,  7,  108 

posterior,  108 

superior,  108 
occipital,  158 
parotid,  158,  260,  366 
space,  perichorioidal,  578 
sternal,  107,  108 
submaxillary,  225, 230, 283,  366 
submental,  228 
supraclavicular,  147 
of  thorax,  10,  108,  257 
thoracic  visceral,  257 
Lymph  vessels  of  lips,  366 
vessels,  pulmonary,  38 


Lymph  trunks,  left  common  jugular, 
106 
left  subclavian,  106 
right  jugular,_  108,  257 
right  subclavian,  108,  257 

Lyra,  498 

Macula  lutea,  580 
Magendie,  foramen  of,  539 
Malleus,  552,  554,  555,  556,  557,  565 

handle  of,  549,  565 

head,  555 

lateral  process  of,  549 

processus  lateralis,  554,  555 

anterior,  555,  556,  565 
Mammillary  bodies,  452,  453,  497, 

503,  504 
Manubrium,  549,  554,  555,  557 
Marshall,  oblique  vein  of,  90 

vestigial  fold  of,  90 
Mastoid  antrum,  565 

air  cells,  555,  559,  560 
Meatus,  external,  acustic,  259 
internal  acustic,  562,  563,  565,  568 
nasi,  397 

inferior,  399 
middle,  397 
superior,  297 
naso-pharyngeal,  400 
Mediastinal  lymph  glands,  10,  89 
pleura,  14,  23,  25,  33,  46,  49,  50, 

70,  76,  77,  84,  85,  ^^ 
space,  14 
Mediastinum,  10,  44 
anterior,  11,  45,  46 
inferior,  10,  45 
middle,  ii,  45 
posterior,  i,  11,  26,  30,  45 
superior,  10,  45,  46 
Medulla  oblongata,  520 

antero-median  groove  of,  521 
anterior  area  of,  522 
central  canal,  521 
closed  part,  520 
decussation  of  pyramids,   520, 

522 
external    arcuate    fibres,    438, 

528 
floor   of  fourth  ventricle,   526- 

528 
formatio  reticularis,    510,    543, 

545 
foramen  cascum,  521 

fossa  rhomboidalis,  536,  537 

funiculus  cuneatus,  525,  526 

gracilis,  526 


INDEX 


6oi 


Medulla  oblongata^ 

funiculus  lateralis,  525 
of  Rolando,  526 

furrows,  521 

grey  matter,  540 

internal  structure,  540 

lateral  area  of,  524 

lemniscus  et  tractus  cerebello- 
spinalis,  512,  525,  545 

nuclei,  522 

olivary  eminence,  525,  526,  528 

open  part,  536-539 

origin  of  nerves,  522 

posterior  area  of,  526 
median  fissure  of,  521 

pyramidal  tract,  522 

pyramids,  522,  528 

raphe,  540,  542 

restiform  body,  525 

structure  of,  540,  541,  542,  543 

tubercle  of  Rolando,  527,  531 

white  matter,  540 
Medulla  spinalis,  186,  187,  194 
differences  in  surfaces,  194 

internal  structure,  194 
grey  matter  of,  196 
white  matter  of,  199 
Medullary  centre,  461 
external,  576 
internal,  576 
laminte,  516 
vela,  535 
Meibomian    follicles.       See    Tarsal 

glands 
Membrana  chorio-capillaris,  579 
flaccida,  556 
tympani,  556 
Membrane,  crico-thyreoid,  297,  415 
anterior,  360,  361 
costo-coracoid,  161 
flaccida,  553,  554 
hyaloid,  581 
intercostal,  anterior,  4 

posterior,  5,  29,  109,  no 
nictitans,  120 
of  Shrapnell,  556 
posterior    atlanto- occipital,    179, 

181,  355>  360,  361 
tectoria,  362 
thyreo-hyoid,  229,  243,  296,  413 

417 

tympanic,  270 
Meninges  of  brain,  201,  414 

of  spinal  medulla,  183 
Mesencephalon,  459,  506,  520 
Middle  ear,  546,  550 


Mitral  valve,  80,  92 
Moderator  band,  71,  74 
Modiolus,  568 
Molar  salivary  glands,  133 
Monticulus  of  cerebellum,  529 
Morgagni,  sinus  of,  372,  382,  383 
Motor  decussation,  542 
Mouth,  364 
floor,  367 
roof,  368 
tongue,  431 
vestibule,  364,  366 
Muco-periosteum  of  nose,  400 
olfactory  region,  400 
respiratory  region,  400 
Muscle  or  Muscles — 

angular  head  of  quadrate  muscle, 

124 
antitragicus,  155 
ary-epiglotticus,  415,  416,  429 
aryteenoideus,  429 
obliquus,  415,  416 
transversus,  415,  416,  417,  420, 
429 
ary-vocalis,  418 
auricularis  anterior,  154 
posterior,  154 
superior,  154 
buccinator,    123,    127,    132,   261, 

.  270,  277,  372,  373 
caninus,  123,  128 
chondro-glossus,  435 
ciliary,  572,  578,  583 

of  eyelid,  376 
constrictor,    middle   of  pharynx, 
234,  281,  290,  291,  297,  303, 
315,  371,  372,  373 
inferior  of  pharynx,  234,  246, 

303>  314,  315.  371,  372,  413, 

414 
superior  of  pharynx,  132,  289, 

297,  299,  304,  311,  371,372, 

373,  382,  383 
crico-arytaenoideus  lateralis,  415, 

418,  419,  422,  429 
posterior,  415,  418,  422,  429 
crico-thyreoid,  230,  314,  413,  414, 

417,  429 
depressor  septi  nasi,  123 
digastric,  230,  238,  259,  262,  264, 

274,  278,  280,  281,  282,  286, 

294,  297,  300,  303,  305,  306, 

307,  316 
dilatator  pupillae,  578 

tubL-e,  384 
of  ear,  extrinsic,  154 


6o2 


INDEX 


Muscle  or  Muscles — 

of  ear,  intrinsic,  155 
epicranius,  122 

of  eye,   lateral  rectus,   335,  340, 
341,  344,  345,  346 
superior,    335,    337,    338,    339, 

344,  346 

obliquus   superior  of  eye,  336, 

337,    338,     340,    342,     346, 

348 
medial  rectus,  340,  344,  346 
obliquus  inferior   of  eye,    341,. 

345,  346,  348 
of  face,  120 
frontalis,  122 
genio-glossus,  285,  286,  287,  288, 

290,  291,  292,  434,  435 
genio-hyoid,  285,  287,  290 
glosso-palatinus,  381,  383 
glutaeus  maximus,  178 
helicis  major,  155 

minor,  155 
hyoglossus,   230,   231,   234,   281, 

282,  284,  285,  286,  287,  288, 

289,  290,  291,  292,  310,  311, 

316,  434,  435 
ilio-costalis,  169 
cervicis,  169 
dorsi,  169,  175 
lumborum,  169 
incisivus,  123,  133 
infra-hyoid,  240,  242,  243,  244 
infraorbital     head     of     quadrate 

muscle,  124 
interaccessorii,  177 
intercostal,  4,  109 
interspinals,  176,  177 
intertransversales,  176,  177,  353, 

355 
of  jaw-movements,  274 
of  laryngeal  movements,  429 
lacrimalis,  121 
latissimus  dorsi,  3,  162 
levator  palati,  304 

glandulse  thyroidese,  229,  321 
palpebrse  superioris,   135,    136, 
334,  335,  336,  337,  338,  339, 
346 
scapulse,  149,    150,    162,    238, 

241,  323 
veli    palatini,    307,    373,    382, 

383,  384 
levatores  costarum,  177 
linguales,  290,  292 
longissimus,  169 

capitis,  168,  170,  306,  351 


Muscle  or  Muscles — 

longissimus,  cervicis,  170 

dorsi,  169,  174 
longitudinal   of  tongue,    inferior, 

292,  435 
superior,  434,  435,  436 
obliquus  capitis  superior,   168, 
171,  179,  i8o_ 
externus  abdominis,  3 
capitis      inferior,      174,      179, 
.    180 

of  orbit,  346 
internus  abdominis,  167 
occipitalis,  156 
superior,  of  neck,  180 
of  orbit,  338 
longus  capitis,  246,  308,  351 
colli,   102,   106,  241,  246,  251, 
322,  351,  354 
masseter,  126,  127,  259,  261,  265, 
266,  270,  274,  276,  277,  283, 
298,  302 
mentalis,  123,  133 

levatores  costarum,  177 
of  mouth,  123,  132 
multifidus,  176,  177 
mylo-hyoid,  230,  270,  274,  278, 
280,  282,  284,  285,  288,  290, 
300,  316 
nasalis,  123 

pars  transversa,   123 
pars  alaris,  123 
naso-ciliary,  336 
of  nose,  122 
oblique  superior  of  head,  354 

inferior  of  head,  354 
obliquus  auriculae,  155 
omo-hyoid,  146, 150, 161, 164,  234, 
238,     242,    244,     246,     290, 

413  . 
orbicularis    oris,    12 1,    122,    123, 

132,  136 
oculi,  121,  134 
orbital  part,  121 
palpebral  portion,  121,  134 
pars  lacrimalis,  122,  136 
palato-glossus,  434,  435 
pharyngo-palatinus,  303, 369,  378, 

381,  382,  383 
pectorales,  3 
platysma,  120,  126,  127,  143,  161, 

260,  274 
prevertebral,  351 
pterygoid,  external,  267, 268, 269, 
270,  271,  273,  274,  275,  276, 
277,  278,  546 


INDEX 


603 


Muscle  or  Muscles — 

pterygoid,  internal,  259,  263,  267, 
269,  274,  275,  276,  278,  281, 
282,  283,  289,  293,  298,  299, 

373,  546 
procerus,  122,  123 
quadratus  labii  inferioris,  123,  125 

lumborum,  167 

labii  superioris,  123,  124,  129, 

387 
angular  head,  125,  128 
infra-orbital  head,  125,  128   " 
zygomatic  head,  125 
rectus  abdominis,  3 

capitis  anterior,  238,  241,  308, 

351 

capitis  lateralis,  238,  241,  308, 

inferior,  344 

lateralis,  304 

lateralis  of  neck,  345 

medialis,  344 

posterior  major,  179,  180 

posterior  minor,  180 

superior,  324,  325 
rhomboideus  major,  164 

minor,  164 
risorius,  123,  125,  126,  260 
rotatores  spinae,  176,  177 
sacro-spinalis,  169 
salpingo-pharyngeus,  381 
scalenus  anterior,   34,    106,   235, 
238,  242,  246,  247,  248,  249, 
251,  252,  255,  257,  259,  309, 

322,  323>  354 
medius,  149,  161,238,  241,  257, 

323 
posterior,  149,  323 
semispinalis    capitis,     149,     168, 
170,  171,  172,  174,  178 
cervicis,  171,  172,  174,  176 
dorsi,  171,  176 
serratus  anterior,  3,  149,  161 
posterior,    inferior,     164,     165, 

166,  167 
posterior,  superior,  164, 165, 168 
sphincter  pupillse,  578 
spinalis,  169,  170 
cervicis,  170 
dorsi,  170 
splenius   capitis,    149,    164,    168, 
178,  238,  281 
cervicis,  168 
stapedius,  551,  554,  555,  558 
sterno-hyoid,  46,  47,  48,  239,  242, 
243,  246,  250,  296,  316,  434 


Muscle  or  Muscles — 

sterno-mastoid,    241,     242,    244, 

245,  250,  251,  259,261,281, 

296,  300,  304,  315,  323 
sterno-mastoid  structures,  beneath 

the,  238 
sterno-thyreoid,  46,  47,  48,  239, 

243.  244,  246,  250,  434 
stylo-glossus,  285,  286,  287,  2S9, 

290,  299,  413,  434,  435 
stylo-hyoid,   230,   259,   262,    263, 

280,  281,  282,  284,  286,  297, 

298.  305»  307,  413 
stylo-pharyngeus,  294,   295,   299, 

303>.373.  381 
subcostalis,  29,  306 
subclavius,  3 
subscapularis,  16 
supra-trochlear,  336 
supra-orbital,  336 
temporal,  265,  266,  267,  269,  270, 

274,  276,  277^ 
tensor  veli  palatini,  274,  275,  293 
tarsi,  121,  373,  382,  383, 384, 404 
tympani,  293,  312,  549 
thyreo  -  arytjenoideus,    417,     419, 

422,429 
thyreo-epiglotticus,  418,  422 
thyreo-hyoid,  231,  234,  243,  244, 

296,  314,  413 
tragicus,  155 

transversus  abdominis,  167 
auriculae,  155 
of  tongue,  435 
thoracis,  6,  8,  9,  12,  50 
trapezius,  162,  241,  315 
triangularis,  123,  125,  128,  129 
of  tympanic  cavity,  558 
uvulie,  381,  383 
vertical,  of  tongue,  435 
vocales,  415,  418,  419,  422,  429 
zygomaticus,  123,  125,  128,  129 
Muscular  triangle  of  neck,  222,  226, 

232,  233,  259 
INIyocardium,  92 

Nares,  posterior,  374,  375,  377,  389 
Nasal  cartilages,  140 
cavities,  393 

anterior  apertures  of,  393 

part,  393 
concha?,  395 
floor,  394 
lateral  wall,  395 
posterior  apertures  of,  393,  394 
roof  of,  393 


6o4 


INDEX 


Nasal  fossa,  393 

atrium,  395 

conchse,  396,  397 

inferior  meatus,  399 

infundibulum,  397 

lateral  wall,  395 

middle  meatus,  397 

olfactory  part,  400 

recessus      spheno  -  ethmoidalis, 

399 
respiratory  part,  400 
superior  meatus,  397 
vestibule,  395 
Nasal  septum,  391 
cartilage  of,  391 
construction  of,  391 
olfactory  area  of,  390 
respiratory  area  of,  390 
vessels  and  nerves  of,  392 
Nasal  vestibulum,  395 
Naso-lacrimal  duct,  140 
Naso-pharynx,  375 
Neck,  141 

anterior  triangle,  226 
deep  dissection,  294 
digastric  triangle,  226 
carotid  triangle,  226 
fascise,  224 

infra-hyoid  region,  227 
joints,  356 
mid-line,  226 
muscular  triangle,  226 
occipital  triangle,  168 
posterior  triangle,  142 
side  of,  142 

submaxillary  triangle,  226 
submental  triangle,  226,  227 
supraclavicular  region,  224 
suprahyoid  region,  227 
surface  anatomy,  224 
Nerve   or  Nerves,  abducent,   212, 
215,  218,  327,  330,  345,  346, 

386,  457 

accessory,  145,  146,  150,  162, 
213,  218,  232,  235,  239,  262, 
281,  300,  304,  307,  309,  310, 
312,  313,  315,  455,  456 

acromial,  182,  228 

acusticus,    213,    215,    218,    456, 
562,  563,  565 
cochlear  division,  565 
vestibular  division,  565 

anterior  cutaneous,  4,  no 

anterior  thoracic,  160 

alveolar  inferior,  267,  268,  276, 
277,  278,  279,  293 


Nerve  or  Nerves — 

alveolar  superior,  388 

anterior,  388 

middle,  388 

posterior,  388 
aortic,  100 

auricular    of    auriculo  -  temporal, 
277 

great,  126,  143,  145,   146,  151, 
156,  235,  239,  241 

of  great  occipital,  156 

posterior,  154,  156,  157 

of  small  occipital,  239,  241 

of  vagus,  312,  313 
auriculo-temporal,  127,   156,  261, 
267,  274,  276,  277,  293 

branches  of,  277 
axillary,  160 
to  azygos  uvulse,  383 
brachial,    109,     147,     157,     160, 

323 
buccinator,    128,    134,  267,    268, 
276,  277 

of  facial,  126,  128 

of  sympathetic,  314 
cardiac,  30,  33,  65,  ^-j,  89,  250 

inferior,  319 

middle,  318 

of  vagus,   30,   33,   87,  89,  99, 
100,  250,  314,  315 

superior,  317,  318 
carotic  external,  317,  318 

internal,  3x7,  318.  3^5 
carotico-tympanic,  312,  386 
cerebral  superficial  origins,  454 
cervical,  353 
cervical,  first,  353,  522 

anterior  branches,  324,  325 

loop  between  first  two,  353 

posterior    divisions,    162,    173, 

174 
chorda   tympani,    549,   551,   552, 

565 
ciliary,  141,  149,  161,  578 

long,  339,  340 

short,  341 
clavicular,  274,  278,  290,  293 
coccygeal,  178 
cochlear,  565 

communicans  hypoglossi,  308,  316 
communicating    of    9th    to    7th, 

311 

communication     of    hypoglossal, 

316 
cords  of  brachial  plexus,  160 
cranial,  123,  456 


INDEX 


605 


Nerve  or  Nerves — 

cranial,  superficial  origin  of,  454, 
455,  456,  457,  458,  459 

cutaneous  colli,  143,  145,  151, 
224,  235,  239,  241 

descendens  hypoglossi,  239,  243, 

descending    of    cervical    plexus, 

143 
to  digastric,  267,  268,   276,   277, 

278,  279,_293_ 
dorsal,  posterior  divisions  of,  174 

scapular,  147,  160,  164,  323 
ethmoidal,  344 
anterior,  340,  402 

medial  nasal,  393 
posterior,  340 
long  thoracic,  323 
of  face,  126 

facial,   213,   215,   218,   263,   281, 

282,  313,  338,  456,  457,  557, 

558,  561,  562,  563,  564 

buccal  branches,  127,  128,  261 

cervical  branches,  127,1261,  294 

division,  184,  198,  262 
cervico-facial  division,  261 
communicating     branches     of, 

.564 
facial,  communicating  with  auri- 

culo-temporal,  277 
of  great  auricular,  126,  146,  241 
intrapetrous  part,  562,  563,  564 
mandibular  branches,  127,  128, 

129,  261 
muscular     to    stylohyoid     and 

digastric,  262,  281 
posterior  auricular,  262,  301 
sensory  root,  215 
superficial  origin,  458 
temporal   branches,    127,    128, 

137,  156,261  _ 
temporo-facial  division,  261 
zygomatic  branches,    127,   128, 

137,  261 
frontal,  330,  334,  336,  346 
glosso-pharyngeal,  213,  215,  218, 

277,  281,  286,  304,  306,  307, 

309,     310,     311,     435,    436, 

455 
ganglion,  superius  of,  312 
lingual  branches,  311 
petrous  ganglion,  312 
superficial  origin,  458,  522 
tympanic  branch,  312,  563 
of  heart,   33,  43,  65,  78,  85,  S7, 
89,  96-99,  100 


Nerve  or  Nerves^ — 

hypoglossal,  213,  215,  218,  220, 
231,  232,  233,  244,  281,  282, 
284,  285,  287,  288,  290,  291, 
292,  294,  300,  304,  305,  306, 
307,  309>  3io>  314,  316,  317. 
351,  355,  435,  436,  455,  522 
superficial  origin,  457,  522 
incisor,  279 
infra-mandibular,  264 
infra-orbital,  128,  129,  138,  387 
nasal  branches,  128 
orbital  branches,  128 
palpebral  branches,  128 
plexus,  1 28 
infra-trochlear,  137,  138,  340 
intercostal,  28,  no 

second,  no 
intercosto-brachial,  no 
of  Jacobson,  312,  563 
labial,  129 
lacrimal,  137,  138,  330,  335,  336, 

346 
laryngeal,  external,  232,  234,  243, 

295,  314 
inferior,  315,372,  413,  421,  422 
internal,    232,    295,    304,    314, 
372,  413,  421,  422,  435,  436 
laryngeal,  recurrent,  2,  33,  49,  78, 
87,  89,  96,  100,  108,245,  246, 
250,  257,  258,  314,  315,  421 
superior,  232,  295,  304,  314,318 
internal  branch  of,  421 
lar}-ngo-pharyngeal,  317,  318 
lateral  cutaneous,  4,  6,  no 

nasal  of  internal  ethmoidal,  481 
to  levator  palati,  380 

scapulae,  151 
lingual,  267,  274,  276,   278,   279, 
282,  284,  285,  286,  288,  289, 
290,  292,  293,  434,  435,  436, 

565 

branches  of,  289 

of  ninth,  314 

of  vagus,  316 
long  thoracic,  160 
lumbar,  150,  166 

posterior  divisions  of,  175 
malar,  261,  263,  265,  347 
mandibular,  212,  274,  275-278,  293 
masseteric,  267,  276 
mastoid,  no,  136 
maxillary,  212,  403 
medial  cutaneous,  of  arm,  160 

of  forearm,  161 
median,  of  arm,  160 


6o6 


INDEX 


Nerve  or  Nerves — 

meningeal  branch  of  trigeminal, 

327,  330,  385 
of  vagus,  313 
of  hypoglossal,  316 
mental,  128,  129,  279 
mylo-hyoid,   230,   276,  278.   281. 
284  •      '  ' 

musculo-cutaneous,  of  arm,  160 
nasal  of  anterior  superior  alveolar, 
401 
external,  341 
internal,  341 
of  infra-orbital,  129 
posterior  inferior,  405 
superior,  401,  402,  403 
naso-ciliar>^   140,  330,  339,   340, 

341,  345.  346,  386 
palatine,  392,  401,  402,  403 
occipital,  great,  156,  161,  162,  174 
small,  143,  145,  146,  151,  156, 

239,  241 
smallest,  156,  161 
oculo-motor,  210,  212,  218,  326, 

327,  330,  331,  332,  335.  338i 
345,  346,  347,  386,  446,  458 
nucleus  of,  509 

oesophageal,  99,  109 

olfactory,  208,  218,  392,  401,  458 

to  omo-hyoid,  146,  150 

ophthalmic,  212,  386 

optic,    208,   218,   339,   341,   458, 

572    ..   . 

superficial  origin,  458 
to  palate,  380,  383 
palatine,  anterior,  402,  403,  404, 

405 

great,  380 

middle,  383,  404 

posterior,  383,  404 

small,  380 
palpebral,  129,  138 
parotid,  277 
pericardiac,  34,  99 
petrosal,  external  superficial,  318, 
333,  386,  564 

great  deep,  333,  386,  405,  564 

great  superficial,  212,  332,  385, 

405 

small  superficial,  333 
phar}-ngeal,  311 

of  phar}-ngeal  canal,  405 
of  glosso-phar}-ngeal,  295.  315 
of  sympathetic,  315 
of  vagus,   295,   304,   306,   314, 
315=  383 


Nerve  or  Nerves — 

phrenic,  2,  10,  23,  25,  30,  2,3,  34, 
43,  49,  50.  70,  87,  88,  89, 
239,  240,  241,  250,  251, 
253,  254,  255,  257,  258,  309, 

323 

pneumogastric.    See  Xerve.  ^  agus 

long  thoracic,  147 

pter}-goid,  293,  333 

of  pter}-goid  canal,  386,  393,  405 

pulmonar}',  43,  99,  ico,  loi 

radial,  160 

roots  of  accessor}-,  522,  526 

glosso-pharyngeal,  522,  526 
vagus,  522,^526 
sacral,  177 

posterior  branches  of.  177 
to  scalenus  medius,  151 

posterior,  151 
of  scalp,  156 

spheno-palatine,  3S8,  403 
spinal,  5,  189,  192 

anterior  primary  divisions,  109, 
192 

classification,  189 

exits  from  vertebral  canal,  190 

ganglia,  185,  189,  192 

origin  from  cord,  189 

posterior  primary  di\"i5ions,  173, 
174,  178,  192 

roots,  185,  189 
spinal  accessor}'.     See  Accessory 

accessory  part,  215 

spinal  part,  215 
spinosus,  275,  333 

to  external  pterygoid,  277 

to  internal  pter}-goid,  275,  276 
splanchnic,  26,  28,  32,  70 

great,  28 

lowest,  28 
to  stapedius,  564 
sternal,  145 
stylo-hyoid,  230,  285 
to  stylo-phar}Tigeus,  311 
to  subclavius,  147,  161 
sub-occipital,  172,  173,  179,  180, 

190 
subscapular,  160 

supracla\"icular,  of  brachial  plexus, 
145,  149,  161 

of  cer^dcal   plexus,    143,    151, 
161,  239,  241 
supra-orbital,  121,  137,  13S,  156 
supra-scapular,  147 
supra-trochlear,    137,     138,     156, 
340,  344 


INDEX 


607 


Nerve  or  Nerves — 

sympathetic.     See  Sympathetic 

temporal,    of  auriculo- temporal, 
277 
of  buccinator,  277 
deep,  267,  276 
of  facial,  137,  156,  261 
of  orbital,  334,  350,  3SS 

to  tensor  palati,  293 
tympani,  293 

thoracic  tirst,  109,  254,  257 

th}T:eoid,  31S 

thjTTeo-hyoid,  316 

tonsillitic,  311 

to  trapezius,  151 

trigeminal,   212,    218,    329,    330, 

457,  529 
mandibular  division,  329 
maxillary  division,  329,  330 
motor  root,  215,  329 
ophthalmic    dix-ision    of,    326, 

327,  329,  330,  336 
roots  of,  328 

semilunar  ganghon,  211,  212 
sensory  root,  212,  215,  328 
tractus  spinalis  of,  527 

for  temporo-mandibular  joint,  277 

thoraco-dorsal,  160 

trochlear,  211,  212,  215,  218,  326, 

327,  330,  332,  335,  336,  346, 
386,  446,  457,  506,  530 
roots  of,  53S 
superficial  origin,  457 
tympanic,  312 
ulnar,  160 

vagus,  2,  10,  23,  25,  30,  32,  33, 
35>  49,  89,  100,  106,  loS, 
213,  215,  218,  232,  239,  245, 
252,  257,  258,  300,  304,  307, 
309,  310,  312,  313,  315,  435, 
456 
ganglion  jugulare,  313 

nodosum,  313 
left,  30,  99 
right,  23,  99 
superficial  origin,  455 
thoracic  branches  of,  99 
vascular  of  hypoglossal,  316 
vestibular  division  of  acustic,  565 
zygomatic,  334,  350,  38S 
zygomatico-temporal,    156,    266, 
267,  350 
-facial,  350 
Nictitating  membrane,  120 
Nodule  of  cerebellum,  533 
Nose,  cartilages  of,  140,  391 


Nose— 

conchce  of,  401 

fossse.     See  Nasal  fossce 

septum,  390,  401,  402 

vestibule,  390 
Nostril,  390 
Notch,  preoccipital,  470,  473 

of  Rivinus,  553,  554 
Nucleus,     amygdaloid,    491,    494, 
512,  514 

auditory,  538 

caudate,  4S8,  489,  491,  494,  502, 
512,  513,  514,  515,  518,  538 

cochlear,  512 

cuneatus,  527 

dentatus  of  cerebellum,  450,  454, 
512,  514,  515,  517,  518,  539 

glosso-pharyngeal,  538 

gracihs,  527,  541 

hypoglossal,  537      _ 

of  lens,  584 

lentiform,  514,  515,  517,  518 

oculo-motor,  509 

oHvary,  543 
accessory,  541 

of  optic  thalamus,  519 

pontis,  545 

pulposus,  115 

ruber,  512 

trigeminal,  509 

trochlear,  509 

vagus,  538 
Niihn,  gland  of,  434 

Obex,  53S 

Oblique  sinus  of  pericardium,   58, 

59,  S9 
Obliterated   ductus   arteriosus,    t^^i^ 

77,7s 
Occipital  lobe,  450,  462 

pole,  465 

sinus,  183,  216,  217 

triangle,  163 
QEsophageal  plexus,  99-102 
(Esophagus,  2,  10,  17,  23,  26,  29, 

30,  31,  32,  39,  40,  49,   50, 
58,  85,  Sj,  89,  96,  99,  100, 
loi,  104,  106 
Olfactory  Inilb,  322,  439,  469,  477 
lobe,  41S 
striie,  477,  478 
tract,  439,  469,  477 
trigone,  478 
Olivary  eminence,  524,  525,  526 

nucleus,  543 
Olive,  524,  525,  526 


6o8 


INDEX 


Olive,  superior,  545 
Omental  bursa,  104 
Opercula  insulse,  463 

frontal,  464,  490 

fronto-parietal,  463,  475,  490 

orbital,  464,  490 

temporal,  463,  475,  490 
Optic  chiasma,  452,  505 

disc,  580,  581 

entrance,  572,  578,  579 

thalamus,  417,  450,  487 

tract,  452,  507,  508 
Optic  nucleus — 

lateral  root,  507,  508 
medial  root, 507,  508 
Ora  serrata,  580,  581 
Oral  fissure,  365 
Orbit,  333 
Orbital  operculum,  464,  490 

periosteum,  334 
Ossicles,   auditory,   546,    550,    554, 

555,  556 
Ostium  pharyngeum,  376 
Otic  ganglion,  276,  277,  279,  293, 

383 

Palate,  hard,  373 

soft,  375,-  380,  382 
Palatal  aponeurosis,  382 
Palpebrae,  119,  134 
Palpebral  commissures,  119 

conjunctiva,  119 

fascia,  135 

fissure,  119 

lateral  palpebral  raphe,  121 

medial  palpebral  ligament,  121 
Papillae  foliatte,  432 

incisive,  368 

lacrimalis,  120 
Papillae  vallatae,  432 

conical,  432 

filiform,  432 

foliatae,  431 

fungiform,  432 
Papilla  nervi  optici,  580 
Paracentral  lobule,  449 
Paramedian  sulcus  of  spinal  medulla, 

195 
Parietal  lobe,  450 

lobule,  450 
Parieto-occipital  fissure,  462 
Parotid,  accessory,  261 

duct,  127,  261 

fascia,  126 

gland,  126,  127,  233,  259,  281 

lymph  glands,  257 


Parotid,  pterygoid  lobe  of,  263 
space,  259,  262,  281 
surfaces  of,  260,  262 
Pars    basilaris    of    inferior    frontal 

gyrus,  469 
Pars  ciliaris  retinae,  580 

mamillaris  hypothalami,  520 
membranacea  septi,  74,  83 
orbitalis  of  inferior  frontal  gyrus, 

469 
triangularis     of    inferior    frontal 
gyrus,  464 
Peduncle  of  brain,  446,  447 
Peduncles  of  cerebrum,  210,  212, 
_  452,  500,  501 
basis  pedunculi,  210 
tegmentum,  210,   503,   508,   509, 

5io»  512 
Pericardium,   10,  25,   26,   30,   33, 

38,  50,  98,  104 

bare  area  of,  50 

fibrous,  50,  70,  75»  83 

oblique  sinus,  58,  59,  89 

parietal,  52,  89 

serous,  51,  59,  70,  75 

transverse  sinus,  54,  59,  76 

vestigial  fold,  92 

visceral,  52,  89 
Perilymph,  546,  566 

vibrations  of,  569 
Pes  anserinus  hippocampi,  49 1 ,  492, 

493,  497 
Petrosal  sinus,  inferior,  312 

superior,  326 
Petrous  ganglion,  312,  313,  317 
Pharyngeal  aponeurosis,  370 

bursa,  373,  376 

plexus,  309,  311,  314 

tonsil,  376 
Pharynx,  369 

bucco-pharyngeal  fascia,  370 

constrictor  muscles,  370,  371 

glands,  375 

interior  of,  374 

isthmus,  384 

laryngeal  part,  378 

lateral  recesses,  376 

lymphoid  follicles,  376 

muscles,  371 

naso-pharynx,  375 

oesophageal  opening,  379 

openings,  370,  375,  376 

oral  part,  377 

recess  of,  376 

relations  of,  369 

roof,  376 


INDEX 


609 


Pharynx — 

tonsil,  376 

veins,  370 

walls,  370 
Phrenico-costal  sinus,  16 
Pia  mater  encephali,  442 

spinalis,  186 
Pillars  of  fauces,  368 
Pineal  body,  500,  503,  505 
Pinna,  153 

extrinsic  muscles  of,  153 

intrinsic  muscles  of,  153 
Piriform  recess,  379 
Pleura,  7,  11,  12,  33 

apex  of,  15,  257 

base  of,  16 

cervical,  15,  248,  250,  257 

costal,  12,  25 

diaphragmatic,  16 

dome  of,  309 

lines  of  reflection,  14,  17,  18,  19 

mediastinal,  14,  23,  25,   33,   46, 
.  49,  50,  70,  76,  n,  84,  85,  %-] 

parietal,  12,  14 

pulmonary  ligament,  14 

relations,  76 

visceral,  11,  14,  104,  105 
Pleural  cavities,  12 

sac,  12 
Plexus,  basilar,  venous,  183,216,217 

brachial,  109,  147,  151,  160,  323. 
See  also  vol.  i.  p.  28 

buccal,  277 

cardiac,  deep,  65,  85,  89,  96,  100, 

loi,  315 
superficial,  33,  43,  65,   ']%,  85, 

87,  315 

carotid,  247,  296,  341,  386 
external,  318 
internal  (nervous),  385 

cavernous,  331,  332,  385,  386 

cervical,  151,  239,  240 

communicating  branches,  241 
deep  posterior  branches,  151,241 
muscular  branches,  241 
superficial  branches,  143,  151, 
241 

chorioid,  488,  489,  492,  493,  494, 
499,  502 

coronary  of  heart,  left,  65.  loi 
right,  65,  85,  loi 

diaphragmatic,  34 

hypoglossal,  316 

infra-orbital,  128,  129,  387 
branches  of,  129 

internal  vertebral  (venous),  182 

VOL.   II — 39 


Plexus — 

intraspinal  (venous),  182 
oesophageal,  99,  100,  102,  104 
pharyngeal,  309,  311,  314,  S^S 

nervous,  370 
position  of,  16 
posterior  sacral,  178 
posterior  vertebral  (venous),  176, 

178 
pterygoid  (venous),  132,  271,  370, 

389 
pulmonary,  anterior,  43,  99,  100, 

lOI 

posterior,  43,  98,  100,  10 1 
renal,  28 

spinal  (venous),  182 
suboccipital  (venous),  157,  173- 
submaxillary  sympathetic,  284 
tympanic,  386 
vertebral  (venous),  355,  356 
sympathetic,  355 
Plica  sublingualis,  288,  289 
fimbriata,  368 

of  tongue,  431 
lacrimalis,  140 
semilunaris,  119,  120 
triangularis,  378 
Piicse  ventriculares,  407,  40S,  409, 
411,  419,  421 
vocales,  407,  409,  410,  411,  419, 
421 
Poles  of  cerebrum,  465 
of  eyeball,  570 
occipital,  465,  473,  474,  476 
temporal,    465,    475,    479,    485, 

487,  494 
Pons  Varolii,  212,  437,  528 
brachium  pontis,  528 
bundle,  medial  longitudinal  of, 

545 

corpus  trapezoidum,  545 
fibres,  superficial  transverse  of, 

545 
longitudinal  of,  545 
trapezial  of,  545 
floor  of  fourth  ventricle,  536 
internal  structure,  544 
lemniscus,  542,  545 
nuclei,  545 
pyramidal  tract,  544 
raphe,  540,  544^ 
reticular  formation,  543 
substantia  ferruginea,  545 
tegmental  part,  545 
transverse  fibres,  545 
Posterior  longitudinal  bundle,  544 


6io 


INDEX 


Prsecuneus,  449,  470,  472,  473,  477, 

478 
Praeoccipital  notch,  473,  490 
Pretracheal  fascia,  229,  230,  235 
Prevertebral  fascia,  235,  236,  237 
Process,  anterior  of  malleus,  556 
ciliary,  577,   579,  581,  582,  583, 

584. 
cochleariformis,  55^5  55^ 
helicis  caudatus,  155 
lenticularis  of  incus,  557 
muscular,  of  arytaenoid,  428 
vocalis,  of  arytaenoid,  428 

Promontory     of    tympanum,     552, 
568 

Prosencephalon,  520 

Prussak,  striae  of,  554 

Pterygoid  lobe  of  parotid  gland,  263 
plexus,    venous,    132,    271,    370, 

387 
Pterygo-maxillary  region,  152,  263 
Pulley  of  superior  oblique,  335,  339 
Pulvinar  of  thalamus,  507 
Puncla  lacrimalia,  120,  139 
Pupil,_  578 

sphincter  and    dilatator    muscles 
of,   578 
Putamen  of  thalamus,  516 
Pyramid  of  cerebellum,  533 
decussation  of,  533,  534 
of  medulla,  523 

of  tympanum,  551,  552,  558,  564 
Pyramidal  lobe  of  thyreoid,  321 
tract,  544 
crossed,  544 
direct,  544 

Quadrate  lobule  of  cerebellum,  532 
Quadrigeminal  bodies,  506,  507 
brachia  of,  506,   507 

Radiate  ligament,  113 
Radiatio  corporis  callosi,  483 
Rami  communicantes,  grey,  28 

white,  26 
Raphe,  lateral  palpebral,  121,  134, 

135,  337 
of  medulla,  540,  542 
of  palate,  382 
of  pharynx,  373 
pterygo-mandibular,      132,     373, 

389 
of  tongue,  436 
Recesses,  lateral,  of  fourth  ventricle, 

536 
of  pharynx,  376 


Recessus   epitympanicus,   550,  552, 

555 

ellipticus,  566 

infundibuli,  505 

pinealis,  505 

piriformis,  379 

spheno-ethmoidalis,  399 

sphsericus,  566 

suprapinealis,  505 

triangularis,  505 
Red  nucleus,  512 
Reil,  island  of,  477 
Restiform  body,  527,  528,  529 
Retina,  571,  579,  580 
Rhombencephalon,  458,  520 
Rima  glottidis,  410 

vestibulse,  410 

palpebrarum,  119 
Rivinus,  ducts  of, 

notch  of,  553,  554 
Rolando,  central  fissure  of,  462,  464 

funiculus  of,  199,  200 

substantia  gelatinosa  of,  542 
Root-ganglia,  189,  191 
Root  of  lung,  22 
Roots  of  olfactory  tract,  482 

of  spinal  nerves,  189,   191 
Rostrum  of  corpus  callosum,  458 

Saccule,  569 
Sac  lacrimal,  136 
Salivary  glands,  molar,  133 
labial,  133 
Salpingo-pharyngeal  fold,  376 
Scala  media,  569 

tympani,  568,  569 

vestibuli,  568,  569 
Scalene  tubercle,  313 
Scalp,  132 

blood-vessels,  157 

epicranial-aponeurosis,  158 

fascia,  158,  159 

loose  areolar  tissue,  layer  of,  159 

nerves,  156 

strata,  152,  159 

temporal  region  of,  152 

surgical  anatomy,  153,  159 
Sclera,  571,  572,  573,  574,  579,  578 
Scleral  coat,  572 

sulcus,  573 
Semicircular  canals,  lateral,  561,  567 
Semilunar  valves,  75,  78,  81 
Sensory  decussation,  542 
Septal  cartilage  of  nose,  391 
Septum  atriorum,  69 

nasal,  389 


INDEX 


6ii 


Septum  of  tongue,  436 

pellucidum,   449,  488,  494,  495, 

497 

posterius  of  arachnoid,  186 

ventriculorum,  71,  72,  78,  82 
Sheath,  carotid,  235 
Sibson's  fascia,  36,  251,  257 
Sinus,  aortic,  60,  80 

basilar,  183,  216 

bulb  of,  307 

cavernous,    209,    210,    217,   271, 
325,  326,  327,  329,  330,  331, 

332,  334,  346 
confluens  sinuum,  217 
coronary,  89 

costo-mediastinal,  16,  370 
frontal,  396,  397 
inferior  sagittal,  207,  211,  217 

petrosal,  309 
intercavernous,  326 

anterior,  209,  217 

posterior,  209,  217 
maxillary,  395,  398 
oblique,  of  pericardium,   58,   59, 

occipital,  183,  216,  217 
of  Morgagni,  373,  382,  383 
petrosal,  inferior,  216,  217,   312, 
326 
superior,  211,  217,  326 
petro-squamous,  217 
pharyngeal  venous,  327 
phrenico-costal,  16,  37 
pterygoid  venous,  327 
pulmonary  (Valsalva),  60,  75 
sigmoid  part,  560 
sigmoid  portion  of,  216 
sphenoidal,  397,  399 
spheno-parietal,  211,  217,  326 
straight,     207,     210,     211,     217, 

499 
superior  sagittal,    162,   202,   205, 

206,  207,  217 
transverse,    171,   205,    211,    215, 
217,  307,  560 
of  pericardium,  54,  59,  76 
Space  interpeduncular,  452 
mediastinal,  10 
parotid,  259 
perichorioidal,  572 
subarachnoid,  439 
subdural,  204 
suboccipital,  204 
Spaces  of  Fontana,  574 
Spatia  anguli  iridis,  574,  584 
zonularia,  583 


Spatium  interfasciale  (of  eye),  348 
Spheno-ethmoidal  recess,  399 

sinus,  397,  399 
Spheno-palatine  ganglion,  386,  388, 
.     .     392 

Sphincter  pupilloe,  578 
Spina  helicis,  158 
Spinal  medulla,  28 

anterior  surface,  194 
arteries,  193 
caput  of  columns,  197 
central  canal,  196 
cervical  enlargement,  187 
columns,  196,  197,  199 
commissures,  196 
conus  meduUaris,  188 
direct  cerebellar  tract,  200 
fasciculis  cerebro-spinalis  later- 
alis, 200 
anterior,  200 
cuneatus,  200 
gracilis,  200 
filum  terminate,  188 
fissures,  195 
grey  matter,  196 
internal  structure,  194 
lumbar  enlargement,  188 
meninges,  183 
origin  of  nerves,  189 
posterior  surface,  187 
regions,  198 

substantia  gelatinosa,  197 
sulci,  195 
surfaces,  187 
veins,  194 
white  matter,  199 
nerve-roots,  189 
nerve-trunks,  189,  192 
root-ganglia,  189 
venous  plexuses.     See  Plexus. 
Spiral  canal  of  modiolus,  568 
Splanchnic  ganglion,  28 
Splenium  of  corpus  callosum,  446 
Stapes,  552,  557,  566 
base,  557 
crura,  557 
head,  557 
neck,  557 
Stensen,  duct  of,  261 
Sternal  line  of  pleural  reflection,  18, 

19 

lymph  glands,  107 
Sterno-chondral  articulations,  112 
Sterno-costal  radiate  ligament,  iii 

interarticular  ligaments,  iii 
Straight  sinus,  54,  59,  76 


6l2 


INDEX 


Stratum  pigmenti  iridis,  580 
Stria  longitudinalis   medialis,-  481, 
482,  500 

lateralis,  482,  483 

medullaris,  502 

terminalis,  488,  489,  491,  502, 

513,  514,  578 
olfactory,  477,  478 
Striae  medullares,  538 
longitudinales,  482 
of  Prussak,  554 
Subarachnoid  cisternge,  439 

space,  439 
Subclavian  groove,  40 

triangle,  249 
Subdural  space,  204 
Sublingual   gland,    280,   286,    288, 

289,  290,  292 
Submaxillary  duct,    282,    285,  286, 
288,  289 
ganglion,  282,  284,  285,  318 
gland,   225,  280,  281,   282,    283, 
284,    285,    286,     288,     289, 
290 
nerve  supply,  284,  298 
region,  279 
triangle,  279,  280 
Submental  triangle,  223,  226,  227 
Suboccipital  space,  178 
Substantia  ferruginea,  545 
gelatinosa,  Rolandi,  197,  527 
nigra,  210,  510 

perforata  anterior,  447,  450,  454, 
478,  479,  483,  517,  518 
posterior,  447,  452,  503 
Subthalamic  region,  501 
Sucking  pad  of  fat,  133,  266 
Sulcus  or  Sulci,  of  brain,  461 
callosal,  478 
centralis   insulte,   464,    466,   467, 

469,  470,  471,  472,  477 
cinguli,  465,  466,  469,  479 
circular,  477 
coronary,  68 
diagonal,  469 
fimbrio-dentate,  495 
frontal,  inferior,  467 
middle,  467 
superior,  467 
fronto-marginal,  467 
of  Heschl,  475 
of  spinal  medulla,  195 
intermediate   posterior    of    spinal 

medulla,  199 
great  horizontal,  530,  531 
hypo-thalamic,  505 


Sulcus  or  Sulci — 

intraparietal,  471,  472 
horizontal  ramus  of,  471 
occipital  ramus  of,  471,  474 
lateralis  mesencephali,  506 
limitans   (of  4th   ventricle),   537, 

538 
lunatus,  474 
of  lungs,  41 
occipitalis  transversus,  472,  474 

lateralis,  474 
olfactorius,  396,  469 
olfactory,  477 
orbital,  469 

lateral,  469 
medial,  469 
transverse,  470 
paramedial,  of  cerebrum,  467 
post-central,  inferior,  471,  472 

superior,  471,  472 
postero-lateral  of  cord,  195 
precentral,  467 
inferior,  466,  469 
superior,  466 
rostrales,  469 
scleral,  573 
sub-parietal,  471,  478 
temporal  operculum,  485 
inferior,  476,  477 
middle,  472,  475 
superior,  472,  475,  485 
terminalis  of  heart,  34 

of  tongue,  430 
tympanicus,  553 
valleculae,  530 
venosus  sclerse,  573 
Surface  anatomy  of  neck,  223 
Suprasternal  fossa,  space,  224 
Supratonsillar  fossa,  378 
superior,  317,  318 
inferior,  319 
middle,  318 
Sympathetic,  cervical,  245,  247,  252 
abdominal,  34 
branches  of,  27,  28,  32,  254 
dorsal  branch,  id8 
first  thoracic  ganglion,  no,  257, 

258 
gangliated  cord,  2,  23,  25,  27 
thoracic,    2,    23,    26,    109,    no, 

254 
Synchondrosis  sternalis,  112 

Taenia  of  4th  ventricle,  537 
Tapetum,  483,  490,  574 
of  choiroid,  575 


INDEX 


6i 


Tarsal  glands,  120 
Tarsi,  134 

inferior,  135 

superior,  135 
Tegmentum,  210,  503,  508,  509,  510, 

512 
Tegmen  tympani,  550 
Tela  chorioidea,  442,  447,  497,  498, 
499,  500,  502,  504,  538 

that  which  is  in,  539 
Telencephalon,  520 
Temporal  fascia,  265,  266 

lobe,  462 

notch,  470,  473 

operculum,  463 

pole,  465 

region,  152,  265 
Tensor  tympani,  565 

palati,  547 
Tentorium  cerebelli,  208,  212,  218, 

459 
Thalamencephalon,  458,  520 
Thalamo-mamillary  region,  519 

anterior  tubercle,  502 

lateral  area,  502 

massa  intermedia,  503,  504 

medial  area,  502 
surface,  503 

posterior  extremity,  502 

pulvinar,  502 
Thalamus,  447,  450,  4S7,  488,  489, 

497,  499,  512,  513,  514,  51S, 
520 
epi-thalamus,  520 
meta-thalamus,  520 
Third  ventricle  of  brain,  498,  499, 
500,  502,  503,  504,  505 
tienia  thalami,  500,  501,  502,  503, 
504,  505,  508 
Thoracic  duct,   2,    10,   31,    32,   48, 
246,  250,  313 
ganglia,  312,  314,  317 
Thorax,  i 
cavity,  I,  lO 
inlet,  2 
joints.  III 
lymph  glands,  107 
outlet,  2 
viscera,  10 
walls,  3,  109 
Thymus  gland,  46,  47,  48,  85 
Thyreo-hyoid  membrane,  229,  243, 

296,  413,  417 
Thyreoid    gland,    229,    234,    244, 
246,  252,  253,  297,  319,  320, 
321,  322,  407 


Thyreoid,  cartilage,  229,  234,  244, 

423 
isthmus,  229,  320,  321 
incisura,  423 

laryngeal  prominence,  424 
lateral  lobe,  407 
paramedial  lobe,  407 
prominentia  laryngea,  229 
pyramidal  lobe  of,  321 
Tongue,  429 
dorsum,  430 
frenulum,  288,  431 
glands,  283,  434 
lateral  lobes  of,  319 
mucous  membrane,  430 
muscles,  285,  433,  434 
nerves,  289,  435 
oral  part,  430 
papilh-e,  432 
pharyngeal  part,  430 
relations  of,  319 
septum,  436 
vessels,  321,  435 
Tonsil,  299,  369,  383 
cerebellar,  533 
pharyngeal,  378 
vessels  of,  383 
Topogi'aphy  of  heart,  94 
contluens  sinuum,  211 
Torus  tubarius,  376 
Trabecule  carnete,  72,  79 
Trachea,  2,   10,  17,  23,  49,  85,  87, 

89,  95,  99,  loi,  321 
Tragus,  158 
Transverse  fissure,  499 

sinus    of    pericardium,     54,     59, 

76 
venous  sinus,  171,  205 
Triangle,    anterior,   of    neck,    222, 
226 
carotid,  226,  232,  233,  259 

contents  of,  231 
digastric,  226 

contents  of,  230 
muscular,  of  neck,  226,  234 
occipital,  168 
posterior,  of  neck,  148 

contents  of,  149 
subclavian,  249 
submaxillary,  223 
submental,  223,  226,  227 
suboccipital,  168,  172 
supraclavicular,  149 
suprameatal,  560 
Triangular  fossa,  154 
Tricuspid  valve,  69 


6i4 


INDEX 


Trigonum  collaterale,  490 

habenulae,  502 

hypoglossi,  537 
Trochlea  of  superior  oblique,  339 
Trunk,  dorsal  aspect,  161 
Trunk -ganglion  of  vagus,  313 
Trunks  of  brachial  plexus,  151 
Tube,  auditory,  293,  304,  546,  547, 

549,  551,  558,  559 
osseus  part,  559 
cartilaginous  part,  559 
Tuber    cinereum,    453,     503,     505, 
526 

nodule,  533 

pyramid,  533 

uvula,  533 

vermis,  533 
Tubercle,  amygdaloid,  490,  493 

anterior  of  thalamus,  503 

corniculate,  379 

cuneiform,  379 

intervenous,  67 

of  Rolando,  527 

of  thyreoid. cartilage,  424,  425 

scalene,  313 

of  vermis,  533 
Tympano-malleolar  folds,  554 
Tympanum,  312,  557,  558,  559 

aditus  of,  555,  561 
medial  wall  of,  561 

anterior  wall,  551 

antrum,  557 

cavity,  565 

cavity,  promontory  of,  561 

floor,  550 

jugular  wall,  55° 

lateral  wall,  553 

mastoid  wall,  550 

medial  wall,  552 

membrane  of,  553 

mucous  membrane,  555 

muscles,  558 

ossicles,  555 

posterior  wall,  550 

promontory  of,  552,  568 

pyramid     of,     551,      552,      558, 

564 
roof,  550 

secondary  membrane  of,  553 
stapes,  558 
tegmen  tympani,  550 

Umbo  of  tympanic  membrane,  554 
Uncus,  494 

Uncus  of  hippocampal  gyrus,   478, 
479,  492 


Utricle,  569 
Uveal  tract,  57 1 
Uvula,  368,  380 

of  cerebellum,  533 

palate,  380 

Vallate  papillae,  432 
Vallecula  cerebelli,  520,  530 

larynx,  409 
Valsalva,  sinuses  of,  60 
Valve,  aortic,  87 

bicuspid,  80,  92 

coronary,  68 

mitral,  80,  92 

pulmonary,  75?  7^ 

of  coronary  sinus,  89 

of  the   vena   cava   (Eustachian), 

semilunar,  75,  78,  81 
tricuspid,  69 
Venae  vorticosse,  573 

alveolar  inferior,  267,  270 

anterior,  262,  280,  281 

Vein  or  Veins,  angular,   131,  137, 

157,  344 
anonyma.     See  Innominate 
ascending  lumbar,  1 1 1 
auditory,  215 

auricular,  posterior,  143,  157 
azygos,  10,  23,  26,  29,  40,  44,  70, 
88,  98,  99,  102,  104,  106,  109, 
III 

hemiazygos,    10,   30,   102,   104, 
106,  III 
accessory    hemiazygos,     10,     30, 

102,  104,  106,  III 
basalis,  211,  212 
brain,  internal  of,  499 
bronchial,  30,  iii 
cardiac,  60,  63 
cephalic,  161 
cerebral,  204,  206 

inferior,  326 

internal,  489 

superficial  middle,  326 
cervical  deep,  254 
coronary  sinus,  63 
comitans   nervi  hypoglossi,    290, 
292 

of  occipital  artery,  309 
of  the  medulla  spinalis,  194 

parietal  emissary,  219 

posterior  auricular,  235 
emissary,  162,  172,  216,  219,  326 

anterior,  231,  271 
facial,  126,  131,  225,  292 


INDEX 


615 


Vein  or  Veins — 

facial,    common,   231,   263,    300, 

-   305  >  309 

deep,  132,  271 

posterior,    127,    157,  231,    261, 
262,  263,  271,  294 

transverse,  262 
frontal,  132,  137,  157 
great  central,  499 
hemiazygos,  10,  loi 

accessory,  ill 
inferior  labial,  132 
infraorbital,  242,   245,  247,  250, 
252,  253,  254,  255,  256,  257, 

389 
innominate,    22,   26,  32,    34,   35, 

46,  47,  48,  49,  50,  85,  88,  89, 

96,  99,  106,  III,  239,  313 
intercostal,  30,  32,  no 
anterior,  112 
superior,  30,  32,  35,  48 
intercostal-right  superior,  in 
intraspinal,  178 
jugular,  anterior,  224,  225,  239, 

242,  245,  250,  308 
external,    127,    145,    147,    149, 

161,  225,  235,  239,  255,  261, 

262,  263 
internal,  40,  47,  106,  234,  235, 

239,  242,  243,  245,  246,  247, 

250,  252,  255,  256,  257,  259, 

262,  264,  281,  300,  303,  305, 

307,  309,  310,  312,  313,  315, 

316,  323 
lingual,  231,  292,  294,  305,  309 
lumbar,  176 
magna   cerebri,    210,     212,    218, 

442 
mammary,  internal,  112 
masseteric,  132 
mastoid,  216,  219 
maxillary,     internal,     262,     263, 

271 
mediastinal,  46 
meningeal,  219,  222,  300 
minimae  cordis,  69 
nasal,  205 

oblique  of  Marshall,  90 
occipital,  157,  162,  172 
oesophageal,  30 
ophthalmic,  219,  271,   326,    344, 

345 

inferior,  344 

superior,  339,  344 
palpebral,  132 
pericardial,  30,  48 


Vein  or  Veins — 

pharyngeal,  370 
post-condyloid,  219 
profunda  cervicis,  173 
pterygoid,  132,  271 
pulmonary,  10,  22,  33,  38,  50,  58, 
60,  70,  89,  92 
relations     of    intra -pulmonary 
parts,  99 
raiiine,  231,  292,  294,  305 
retinal,  580 
spinal,   194 

cardiac  veins,  anterior,  64 
great  cardiac  vein,  63 
middle,  63 
small,  64 
facial  vein,  posterior,  126 
oblique  vein,  63 
subcostal,  30 
superior  intercostal,  30,  32,  35, 

8y,  89,  100,  III 
temporal  superficial,  157 
venae  minimae,  cordis,  64,  92 
ventricular  vein,  inferior,  63 
subclavian,  40,  47,  106,  108,  250, 
254,  256,  257,  258,  259,  323 
superficial  parotid,  132 
superior  labial,  132 
supra-orbital,  132,  157 
temporal  middle,  265 
terminalis,  488,  499,  500,  502 
of  thoracic  wall,  no 
thyreoid,  inferior,  47,  88,  96,  229, 

253,  320,  321 
middle,  239,  247,  309,  321 
superior,   231,    245,    297,    309, 

321 
thymic,  48 
transverse  scapular,    161,   225, 

253 
transversa     colli,      161,      225, 

253 
vertebral,  47,  in,  183,  250,  252, 

254,  257 
anterior,  253 

anterior   medullary,    506,   511, 

535 
posterior  medullary,  533,  535 

Vela  medullary,  535 

Velum  palatinum,  380 

muscles  of,  380 

medullary,  inferior,  535 

anterior,  506,  530 

superior,  506,  530 

Vena  cava  inferior,  23,  26,  33,  34, 

39,  54,  58,  65,  67,  70 


6i6 


•   INDEX 


Vena  cava,  superior,  lo,  22,  23,  25, 
26,  29,  34,  39,  44,  46,  55> 
65,  66,  69,  85,   88,   89,  97, 

99 

terminalis,  488,  489 
magna  cerebri,  210,  211,  2i8 
Venffi  vorticosae,  579 
Ventricle,  fifth,  497 
fourth,  536 
floor,  536 
lateral  recess,  536 
roof,  536,  538 
lateral,  485,  502 

bulb  of,  371,  530,  550 
cornua,  487,  490 
floor,  536 
pars  centralis,  488 
trigone,  537 
third,  498,  499,  500,  502,  505 


Ventricle  of  heart,  70,  74,  79 

of  larynx,  412,  421 
Vermis,  529,  530 

cerebelli,  529 
Vertebrae,  355,  356 

aponeurosis,  235,  236,  237 

canal,  181 
Vestibule,  563,  566,  567,  568,  569 

of  labyrinth,  561,  565 

of  larynx,  407 

of  mouth,  121,  127 

of  nose,  395 
Vibrissse,  390,  395 
Visual  centres,  lower,  508 
Vitreous  body,  572,  579,  581 
Vomer,  nasal  organ  of,  391 

Zonula  ciliaris,  578,  579,  581,  582, 
583 


THE    END 


Pj'bited  by  R.  &  R.  Clark,  Limited,  Edinburgh. 


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